Lazanu Sorina

The development of short-wave infrared (SWIR) photonics based on GeSn alloys is of high technological interest for many application fields, such as the Internet of things or pollution monitoring. The manufacture of crystalline GeSn is a major challenge, mainly because of the low miscibility of Ge and Sn. The use of embedded GeSn nanocrystals (NCs) by magnetron sputtering is a cost-effective and efficient method to relax the growth conditions. We report on the use of GeSn/SiO2 multilayer deposition as a way to control the NC size and their insulation. The in situ prenucleation of NCs during deposition was followed by ex situ rapid thermal annealing. The nanocrystallization of 20X(11nm_Ge0.865S0.135/1.5nm_SiO2) multilayers leads to formation of GeSn NCs with similar to 16% Sn concentration and similar to 9 nm size. Formation of GeSn domes that are vertically correlated contributes to the nanocrystallization process. The absorption limit of similar to 0.4 eV in SWIR found by ellipsometry is in agreement with the spectral photosensitivity. The ITO/20x(GeSn NC/SiO2)/p-Si/Al diodes show a maximum value of the SWIR photosensitivity at a reverse voltage of 0.5 V, with extended sensitivity to wavelengths longer than 2200 nm. The multilayer diodes have higher photocurrent efficiency compared to diodes based on a thick monolayer of GeSn NCs.

The nature of dark matter is still an open problem. The simplest assumption is that gravity is the only force certainly coupled to dark matter and thus the micro black holes could be a viable candidate. We investigated the possibility of direct detection of charged micro black holes with masses around and upward the Planck scale (10(-5) g), ensuring a classical gravitational treatment of these objects in the next generation huge LAr detectors. We show that the signals (ionization and scintillation) produced in LAr enable the discrimination between micro black holes and other particles. It is expected that the trajectories of these micro black holes will appear as crossing the whole active medium, in any direction, producing uniform ionization and scintillation on the whole path.

GeSn alloys have the potential of extending the Si photonics functionality in shortwave infrared (SWIR) light emission and detection. Epitaxial GeSn layers were deposited on a relaxed Ge buffer on Si(100) wafer by using high power impulse magnetron sputtering (HiPI-MS). Detailed X-ray reciprocal space mapping and HRTEM investigations indicate higher crystalline quality of GeSn epitaxial layers deposited by Ge HiPI-MS compared to commonly used radio frequency magnetron sputtering (RF-MS). To obtain a rectifying heterostructure for SWIR light detection, a layer of GeSn nanocrystals (NCs) embedded in oxide was deposited on the epitaxial GeSn one. Embedded GeSn NCs are obtained by cosputtering deposition of (Ge1-xSnx)(1-y)(SiO2)(y) layers and subsequent rapid thermal annealing at a low temperature of 400 degrees C. Intrinsic GeSn structural defects give p-type behavior, while the presence of oxygen leads to the n-character of the embedded GeSn NCs. Such an embedded NCs/epitaxial GeSn p-n heterostructure shows superior photoelectrical response up to 3 orders of magnitude increase in the 1.2-2.5 mu m range, as compared to performances of diode based only on embedded NCs.

Detection in short-wave infrared (SWIR) has become a very stringent technology requirement for developing fields like hyperspectral imaging or climate changes. In a market dominated by III-V materials, GeSn, a Si compatible semiconductor, has the advantage of cost efficiency and inerrability by using the mature Si technology. Despite the recent progress in material growth, the easy fabrication of crystalline GeSn still remains a major challenge, and different methods are under investigation. We present the formation of GeSn nanocrystals (NCs) embedded in oxide matrix and their SWIR characterization. The simple and cost-effective fabrication method is based on thermal treatment of amorphous (Ge1-xSnx)(y)(SiO2)(1-y) layers deposited by magnetron sputtering. The nanocrystallization for Ge1-xSnx with 9-22 at. % Sn composition in SiO2 matrix with 9% to 15% mole percent was studied under low thermal budget annealing in the 350-450 degrees C temperature range. While the Sn at.% content is the main parameter influencing the band-structure of the NCs, the SWIR sensitivity can be optimized by SiO2 content and H-2 gas component in the deposition atmosphere. Their role is not only changing the crystallization parameters but also to reduce the carrier recombination by passivation of NCs defects. The experiments indicate a limited composition dependent temperature range for GeSn NCs formation before beta-Sn phase segregation occurs. NCs with an average size of 6 nm are uniformly distributed in the film, except the surface region where larger GeSn NCs are formed. Spectral photovoltaic current measured on SiO2 embedded GeSn NCs deposited on p-Si substrate shows extended SWIR sensitivity up to 2.4 mu m for 15 at. % Sn in GeSn NCs. The large extension of the SWIR detection is a result of many factors related to the growth parameters and also to the in situ or ex situ annealing procedures that influence the uniformity and size distribution of NCs.

The VIS-SWIR photosensing properties of Ge and GeSi NCs embedded in TiO2 films are investigated. For this, we deposit GeTiO2 and GeSiTiO2 films, respectively by magnetron sputtering and then we perform rapid thermal annealing (RTA) for Ge NCs and GeSi NCs formation, respectively. Raman studies and spectral photocurrent measurements were carried out. Ge NCs formation is evidenced in the Raman spectrum of GeTiO2 film annealed at 550 degrees C. The photocurrent spectra measured on the Ge NCs-TiO2 film present four peaks separated by deconvolution. The broad peaks at similar to 700, 890, 1010 nm are due to photo-effects in the Ge NCs-TiO2 film. More than that, the photocurrent increases exponentially with the increase of bias voltage. The cut-off wavelength is similar to 1240 nm. We achieve the extension of the photosensitivity limit to similar to 1310 nm in GeSi NCs-TiO2 films (800 degrees C RTA).

Trilayer memory capacitors of control HfO2/floating gate of Ge nanoparticles in HfO2/tunnel HfO2/Si substrate deposited by magnetron sputtering and subsequently annealed are investigated for the first time for applications in radiation dosimetry. In the floating gate (FG), amorphous Ge nanoparticles (NPs) are arranged in two rows inside the HfO2 matrix. The HfO2 matrix is formed of orthorhombic/tetragonal nanocrystals (NCs). The adjacent thin films to the FG are also formed of orthorhombic/tetragonal HfO2 NCs. This phase is formed during annealing, in samples with thick control HfO2, in the presence of Ge, being induced by the stress. In the rest of the control oxide, HfO2 NCs are monoclinic. Orthorhombic HfO2 has ferroelectric properties and therefore enhances the memory window produced by charge storage in Ge NPs to above 6 V. The high sensitivity of 0.8 mV Gy(-1) to a particle irradiation from a Am-241 source was measured by monitoring the flatband potential during radiation exposure after electrical writing of the memory.

GeSi NCs / TiO2 multilayers with enhanced photocurrent properties were prepared and studied. Multilayers of TiO2 /(GeSi/TiO2)x2 /Si-p were deposited by magnetron sputtering and annealed by RTA at 700 degrees C for GeSi NCs formation. A post-annealing hydrogenation in plasma was performed on multilayers for healing of defects acting as traps and/or recombination centers and consequently producing the photocurrent enhancement. We studied the electrical and photoconductive properties of multilayers annealed by RTA and post-annealing hydrogenated. The current - temperature dependence reveals the conduction mechanisms in GeSi NCs / TiO2 multilayers RTA annealed, i.e. thermal activation of carriers to extended states (0.31 eV activation energy), the electron tunneling mechanism to nearest neighbors (T-1/2 behavior) and Mott variable range hopping (T-1/4 dependence). The photocurrent spectra made on multilayers structures hydrogenated for 10, 20 and 30 min evidence the photocurrent increasing up to 50%, showing that the hydrogenation is a suitable treatment for enhancing photocurrent. All photocurrent spectra present a dominant maximum (920 nm) and two shoulders (similar to 770 and similar to 1060 nm).

Si and Ge nanocrystals in oxides are of a large interest for photo-effect applications due to the fine-tuning of the optical bandgap by quantum confinement in nanocrystals. In this work, dense Ge nanocrystals suitable for enhanced photoconduction were fabricated from 60% Ge in TiO2 amorphous layers by low temperature rapid thermal annealing at 550 degrees C. An exponential increase of the photocurrent with the applied voltage was observed in coplanar structure of Ge nanocrystals composite films deposited on oxidized Si wafers. The behaviour was explained by field effect control of the Fermi level at the Ge nanocrystals-TiO2 layer/substrate interfaces. The blue-shift of the absorption gap from bulk Ge value to 1.14 eV was evidenced in both photocurrent spectra and optical reflection-transmission experiments, in good agreement with quantum confinement induced bandgap broadening in Ge nanocrystal with sizes of about 5 nm as found from HRTEM and XRD investigations. A nonmonotonic spectral dependence of the refractive index is associated to the Ge nanocrystals formation. The nanocrystal morphology is also in good agreement with the Coulomb gap hopping mechanism of T-1/2 -type explaining the temperature dependence of the dark conduction.

GeSi NCs / TiO2 multilayers with enhanced photocurrent properties were prepared and studied. Multilayers of TiO2 /(GeSi/TiO2)x2 /Si-p were deposited by magnetron sputtering and annealed by RTA at 700 degrees C for GeSi NCs formation. A post-annealing hydrogenation in plasma was performed on multilayers for healing of defects acting as traps and/or recombination centers and consequently producing the photocurrent enhancement. We studied the electrical and photoconductive properties of multilayers annealed by RTA and post-annealing hydrogenated. The current - temperature dependence reveals the conduction mechanisms in GeSi NCs / TiO2 multilayers RTA annealed, i.e. thermal activation of carriers to extended states (0.31 eV activation energy), the electron tunneling mechanism to nearest neighbors (T-1/2 behavior) and Mott variable range hopping (T-1/4 dependence). The photocurrent spectra made on multilayers structures hydrogenated for 10, 20 and 30 min evidence the photocurrent increasing up to 50%, showing that the hydrogenation is a suitable treatment for enhancing photocurrent. All photocurrent spectra present a dominant maximum (920 nm) and two shoulders (similar to 770 and similar to 1060 nm).

Trilayer memory capacitors with Ge nanocrystals (NCs) floating gate in HfO2 were obtained by magnetron sputtering deposition on p-type Si substrate followed by rapid thermal annealing at relatively low temperature of 600 degrees C. The frequency dispersion of capacitance and resistance was measured in accumulation regime of Al/HfO2 gate oxide/Ge NCs in HfO2 floating gate/HfO2 tunnel oxide/SiOx/p-Si/Al memory capacitors. For simulation of the frequency dispersion a complex circuit model was used considering an equivalent parallel RC circuit for each layer of the trilayer structure. A series resistance due to metallic contacts and Si substrate was necessary to be included in the model. A very good fit to the experimental data was obtained and the parameters of each layer in the memory capacitor, i.e. capacitances and resistances were determined and in turn the intrinsic material parameters, i.e. dielectric constants and resistivities of layers were evaluated. The results are very important for the study and optimization of the hysteresis behaviour of floating gate memories based on NCs embedded in oxide. (C) 2017 Published by Elsevier B.V.

Photo-induced effects on charging and discharging of nanocrystals (NCs) in capacitor memories with Ge NCs in an HfO2 matrix as a floating gate layer are studied. The sequence of layers HfO2/Ge-HfO2/ HfO2 was deposited on a p-Si substrate using magnetron sputtering. Well separated Ge NCs are obtained after rapid thermal annealing at 600 degrees C. The optoelectric capacitor memories were fabricated with a semi-transparent electrode on top of the structure and an Al electrode on the back side of the Si substrate. Light illumination effects on hysteresis curves were investigated using different operation modes. The hysteresis window increases by increasing the light exposure time. The spectral dependence of the hysteresis window shows the maximum contribution of the light in the wavelength range of 950-1000 nm, corresponding to both contributions from the Si substrate and from Ge NCs. The stored information about the electrical and optical pulses is also investigated in the regime of the flat band potential measurements (retention measurements). It is shown that in our memory structure, the photo-effect on the memory retention corresponds to a tunnelling transfer of negative charges from the Si substrate to Ge NCs, up to a mean value of 1.6 electrons per NC. Published by AIP Publishing.

Trilayer MOS capacitors gate HfO2 / floating gate of Ge nanocrystals in HfO2 / tunnel HfO2 / Si substrate were prepared in the aim to be used for the detection of ionizing radiation. Magnetron sputtering and rapid thermal annealing were used for their fabrication. Capacitance-voltage measurements showed that Ge nanocrystals are the most important charge storage centres in our structure. The possibility to use these trilayer MOS capacitors as dosimeters was investigated, and the sensitivity to alpha particle irradiation was extracted.

High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO2 were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO2/floating gate of single layer of Ge QDs in HfO2/tunnel HfO2/p-Si wafers. Both Ge and HfO2 are nanostructured by RTA at moderate temperatures of 600-700 degrees C. By nanostructuring at 600 degrees C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 x 1015 m(-2) is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO2 nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO2 NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO2 NCs boundaries, while another part of the Ge atoms is present inside the HfO2 lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8. +/-. 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO2, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.

The influence of light illumination on the programming of a capacitor floating gate memory based on Ge nanocrystals in HfO2 was studied. The capacitor was fabricated on a c-Si substrate by magnetron sputtering deposition of a layer sequence of HfO2/Ge-HfO2/HfO2 and post-growth rapid thermal annealing for nanocrystals formation at 600 degrees C. The illumination of the structure was performed through a semi-transparent Au contact (20% transparency). A maximum value of the light- induced change of 90% in C-V curve was obtained for 5 mW/cm(2) illumination during +5 V writing programming. The effect of the light exposure on the relative change of the C-V curve can be increased by reducing the writing time at 1 min.

The electrical and photosensing properties correlated with structure and morphology of TiO2/(GeSi/TiO2)(2) multilayers are investigated. The multilayers are prepared by magnetron sputtering followed by rapid thermal annealing. Studies of Raman spectroscopy, transmission electron microscopy and X-ray diffraction are carried out. Measurements of dark current versus voltage and temperature are done. The photosensing properties are studied by measuring photocurrent spectra at different temperatures. We obtain multilayers with 10 - 15 nm Ge0.6Si0.4 nanocrystals (NCs) by annealing at 800 degrees C. We evidence the tunneling mechanism between neighbor NCs (T-1/2 law) in the dark current-temperature dependence. The photocurrent spectrum has a maximum with position shifting from 940 to 980 nm when the measurement temperature increases from 150 to 300 K, being due to the GeSi NCs.

The strain in Si containing group-V impurities is a topical subject of study due to its potential applications in quantum computing. In this paper we study Bi-209 implanted Si concerning the correlation between the strain produced by stopped Bi ions and trapping characteristics of the defects resulted from implantation. The depths distributions of stopped ions and primary defects are simulated and the distributions of permanent defects are modelled for Si implanted with low fluence Bi-209 ions of 28 MeV kinetic energy. For comparison, these depths distributions were similarly calculated for I-127 ions with the same fluence and energy, implanted in Si. The results are compared with each other and correlated with the characteristics of traps in these systems, previously obtained. We demonstrate that the intensity of the strain field is the most important factor in changing of trap parameters, while the superposition between the region with strain and the region where defects are located is a second order effect. (C) 2016 Elsevier Ltd. All rights reserved.

The strong correlation between morphology and charge storage properties of HfO2/Ge/HfO2/Si trilayer structures was evidenced. The morphology of structures deposited by magnetron sputtering and electron beam evaporation was tailored by rapid thermal annealing and investigated by transmission electron microscopy, Raman and X-ray photoelectron spectroscopies. The best hysteresis loops (capacitance-voltage characteristics) were obtained for trilayers with high density Ge nanocrystals located in the position of as-deposited Ge layer. The decrease of Ge nanocrystals density narrows the memory window, by spreading Ge atoms into HfO2 matrix (sputtered trilayers), or by Ge atoms expulsion toward HfO2 nanocrystals surface (evaporated trilayers). (C) 2015 Elsevier Ltd. All rights reserved.

The influence of the transient thermal effects on the partition of the energy of selfrecoils in germanium and silicon into energy eventually given to electrons and to atomic recoils respectively is studied. The transient effects are treated in the frame of the thermal spike model, which considers the electronic and atomic subsystems coupled through the electron-phonon interaction. For low energies of selfrecoils, we show that the corrections to the energy partition curves due to the energy exchange during the transient processes modify the Lindhard predictions. These effects depend on the initial temperature of the target material, as the energies exchanged between electronic and lattice subsystems have different signs for temperatures lower and higher than about 15 K. Many of the experimental data reported in the literature support the model. (C) 2015 Elsevier B.V. All rights reserved.

The direct detection of dark matter candidates, for which semiconductor materials are used, is based on the detection of low energy selfrecoils. We show that the corrections to the energy partition curves due to the energy exchange during the transient processes modify the predictions of the standard Lindhard theory. These effects, calculated in the frame of a new model developed by the authors, depend on the initial temperature at which the detector operates, and on the energy of the recoil. Most of the available experimental data accumulated during more than fifty years. support these results.

The structure and charge storage properties of a trilayer structure with Ge nanocrystals embedded in HfO2 oxide were studied. The trilayer structure HfO2/Ge-HfO2/HfO2/p-Si was prepared by magnetron sputtering and subsequent rapid thermal annealing at 600 degrees C. The TEM investigations reveal the formation of Ge NCs embedded in crystalline HfO2 at the position of the Ge-HfO2 layer. The capacitors were made by Al evaporation on both front and backside of the trilayer structure. The C-V characteristics show a counterclockwise hysteresis with large memory window of 0.85 V which is given only by the contribution of the Ge NCs embedded in HfO2. The I-V characteristics show an asymmetric behavior, the currents are three times higher for the negative voltage than the positive one.

One of the methods of direct detection of the massive component of dark matter is the registration of self-recoils in semiconductor detectors at cryogeniC temperatures after the WIMPS scattering. In this contribution, after a short presentation of Lindhard curves, derived from the integro-differential equations of the general theory, we discuss the discrepancies between experimental data and theoretical predictions, as well as the corrections suggested in the literature. A new correction is proposed, which is due to the energy transfer between the electronic and atomic subsystems in the solid during the transient phenomena following the primary interaction, and some numerical results are presented.

We analyse the influence of the strain field on the parameters of trapping centres. The system under study is high resistivity Si implanted with Bi6+ and I6+ ions respectively, of 28 MeV kinetic energy, 3(O) off axis orientation and 5x10(11) ions/cm(2) fluence. The strain field is the consequence of size and mass difference of the irradiation ions in respect to the atoms of the lattice, and the defects are produced during the slowing-down of ions, as a result of the energy transfer from the ion to Si atoms. These results are of interest for the design and manufacturing of microelectronic devices incorporating strain, particularly for quantum computers with qubits based on the interaction of electronic and nuclear spins of group-V donors in Si.

The effects of strain field are studied in Si wafers implanted with heavy iodine and bismuth ions and in multi-quantum well structures. The experimental method of thermally stimulated currents without applied bias is used, and the trapping centres parameters are determined by modelling the discharge curves. In both cases, the strain field produces temperature-dependent parameters of trapping levels. So, due to the high strain field in the neighbourhood of implanted ions, energy levels broaden and cross sections become temperature dependent. In multilayer structures, for the trapping centres corresponding to strain-induced defects both concentrations and capture cross sections are temperature dependent.

Low fluence heavy ions incident on high resistivity Si produce lattice defects which act as trapping centers, and produce also an important local field of strain. The strain field intensity increases with the increase of the difference in atomic size and mass between the ion and the Si atom host. We investigate the correlation between the change of trapping parameters and the strain field. The strain field produced by Bi ions in Si is two times more intense than in Si irradiated with I ions, and effects the Gaussian broadening of trapping levels and the temperature dependence of cross sections.

Multi-quantum well structures and Si wafers implanted with heavy iodine and bismuth ions are studied in order to evaluate the influence of stress on the parameters of trapping centers. The experimental method of thermostimullatedcurrents without applied bias is used, and the trapping centers are filled by illumination. By modeling the discharge curves, we found in multilayered structures the parameters of both 'normal' traps and 'stress-induced' ones, the last having a Gaussian-shaped temperature dependence of the cross section. The stress field due to the presence of stopped heavy ions implanted into Si was modeled by a permanent electric field. The increase of the strain from the neighborhood of I ions to the neighborhood of Bi ions produces the broadening of some energy levels and also a temperature dependence of the cross sections for all levels.

By implanting Bi in Si, a strong strain field due to the bigger atomic mass and size of stopped Bi ions than Si lattice ones is produced, together with irradiation defects. The controlled doping of Si with Bi leads to modern applications such as quantum information processing. Here we show that the parameters of trapping centres are modified under the strain field. In the literature there are no reports on this subject. We irradiated Si wafers with Bi6+ ions of 28MeV kinetic energy, 3 degrees off [100] axis orientation. The depth distributions of stopped ions and of primary defects were simulated. The traps produced by irradiation were investigated using the thermally stimulated currents method without bias. We recorded and modelled the discharge current curves. The strain field was modelled as a permanent and temperature-independent electric field. The traps of V-2, VO/CiCs, and CiOi and other two not assigned were evidenced. We have found that all trapping levels are broadened, and all capture cross-sections are temperature dependent which we attribute to the strong strain field produced by Bi. These results are important and must be taken into account in designing and manufacturing microelectronic devices incorporating strain, including the topical spin qubit ones. Copyright (C) EPLA, 2014

In the modern cryogenic technique the heat deposited as phonons, the ionization and/or light from scintillation signals could be used for detection. Also, the formation of defects in the lattice structure of material is possible. In the case when the ionization signal is used for detection, a bias voltage must be applied and thus the generalised Luke-Neganov effect must be considered with contributions from the energy stored in the semiconductor lattice as stable defects in the form of Frenkel pairs. In the process of interaction between the projectile particle and the target, the transient phenomena by which the energy is transferred producing ionization, heat and defects was investigated in the frame of a thermal spike model. A detailed discussion of the associated difficulties of this analysis is done and the results put in evidence the interplay between the primary energies deposited in the electronic and lattice subsystems. This process affects the effective number of defects and the energy stored, which is taken into consideration in the balance of energy conservation in Luke Neganov effect

N-type silicon single crystals with resistivity higher than 8000 Omega cm were irradiated with ions of Bi6+, of 28 MeV kinetic energy. At this energy, the ions are stopped into the wafer. Being much heavier and bigger than the host atoms, they produce major disturbances into the lattice. On the other hand, the produced collision cascade is the source of lattice defects which act as traps. We investigated them using the method of thermally stimulated currents without applied bias. The results are compared with those obtained from the analysis of silicon irradiated with I6+ ions.

The cryogenic detectors in the form of bolometers are presently used for different applications, in particular for very rare or hypothetical events associated with new forms of matter, specifically related to searches for dark matter. In the detection of particles with a semiconductor as target and detector, usually two signals are measured: ionization and heat. The amplification of the thermal signal is obtained with the prescriptions from the Luke-Neganov effect. The energy deposited in the semiconductor lattice as stable defects in the form of Frenkel pairs at cryogenic temperatures, following the interaction of a dark matter particle, is evaluated and consequences for measured quantities are discussed. This contribution is included in the energy balance of the Luke effect. Applying the present model to germanium and silicon, we found that for the same incident weakly interacting massive particle the energy deposited in defects in germanium is about twice the value for silicon. (C) 2013 Elsevier B.V. All rights reserved.

N-type P-doped silicon single crystals with resistivity higher than 8000 Omega cm were irradiated with I-127(6+) ions of 28 MeV kinetic energy. The penetration of the ions through the target and the processes of energy loss were simulated using the CTRIM Monte Carlo code, and point defect production was calculated in the frame of our diffusion-reaction model. Trapping phenomena were investigated using the method of thermally stimulated currents without applied bias. The modeling of the current-temperature curves takes into consideration both point defects and stress-type trapping centers, produced by the ions stopped into the crystal.

The effects of 5 x 10(11) cm(-2 6+)I(127) ions of 28 MeV kinetic energy on high resistivity (100) Si were studied. The profile of primary defects was simulated. The defects produced by irradiation which act as traps were investigated. Thermally stimulated current measurements without externally applied bias were used, and for this the traps were charged by illuminating samples with 1000, 800, and 400 nm wavelengths. The discharge currents were recorded and modeled, and therefore the parameters of the traps were determined. The presence of I ions, heavier than Si, stopped into the target was modeled as a temperature independent electric field. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772015]

In the present contribution, the peculiarities of the electronic and nuclear energy loss of some "exotic" particles, as well as the transient phenomena produced in materials during their stopping are investigated, for their potential use in detectors. In some cases (e. g. strangelets or fullerene ions), these phenomena are produced directly by the incoming particles, and also by their secondary products, while in others (e. g. weakly interacting massive particles) only by the recoils resulting from their elastic scattering on the nuclei of the target. The analysis is made in the frame of a thermal spike model, as time and space dependencies of the electronic and atomic temperatures in the neighbourhood of the interaction point or of the trajectory of the particle.

Weakly interacting massive particles (WIMPs) and strangelets are two classes of "exotic" particles not yet discovered, and in agreement with theoretical scenarios most probably produced in different early stages of evolution of the Universe. Some peculiarities of their energy loss in the electronic and nuclear interactions with ordinary matter are investigated. For the direct detection of WIMPs the signals produced by the stopping of recoils in matter are used for their identification. The influence of the orientation of the recoil in respect to crystal axes for crystalline silicon (as material for detectors) is analysed as average quantities: energy loss, and as transient thermal effects. For strangelets, the mechanisms of picking-up neutrons during their penetration into matter and the effects on electronic and nuclear stopping are considered. The clarification of the aspects related to the stopping of these hypothetical particles in matter will permit a better interpretation of some experimental results and could also contribute to the search for new techniques or materials for their detection, if they exist. (C) 2012 Elsevier B.V. All rights reserved.

Noble solid gases are promising detector materials to be used in the search for dark matter. In the present paper a systematic analysis of the transient phenomena associated with the stopping of recoils in noble gases in the solid phase is performed for the first time. The investigated energy range of the recoils corresponds to the elastic scattering of WIMPs from the galactic halo in these materials. A thermal spike model, previously developed by the authors, is extended and applied to solid noble gases. Ionization, scintillation and nuclear. energy loss processes are considered and included in the model, as well as the coupling between the subsystems. The development of the temperature pulse in space and time in solid Ar, Kr and Xe is analysed for different energies of the WIMP, and for different initial temperatures of the material. Phase transitions are possible in particular cases. The results of the model could be used as supplementary information in respect to ionization and scintillation, for detection and particle identification.

In current particle physics experiments, silicon strip detectors are widely used as part of the inner tracking layers. A foreseeable large-scale application for such detectors consists of the luminosity upgrade of the Large Hadron Collider (LHC), the super-LHC or sLHC, where silicon detectors with extreme radiation hardness are required. The mission statement of the CERN RD50 Collaboration is the development of radiation-hard semiconductor devices for very high luminosity colliders. As a consequence, the aim of the R&D programme presented in this article is to develop silicon particle detectors able to operate at sLHC conditions. Research has progressed in different areas, such as defect characterisation, defect engineering and full detector systems. Recent results from these areas will be presented. This includes in particular an improved understanding of the macroscopic changes of the effective doping concentration based on identification of the individual microscopic defects, results from irradiation with a mix of different particle types as expected for the sLHC, and the observation of charge multiplication effects in heavily irradiated detectors at very high bias voltages. (C) 2011 Elsevier B.V. All rights reserved.

The trap parameters of defects in Si/CaF2 multilayered structures were determined from the analysis of optical charging spectroscopy measurements. Two kinds of maxima were observed. Some of them were rather broad, corresponding to "normal" traps, while the others, very sharp, were attributed to stress-induced traps. A procedure of optimal linear smoothing the noisy experimental data has been developed and applied. This procedure is based on finding the minimal value of the relative error with respect to the value of the smoothing window. In order to obtain a better accuracy for the description of the trapping-detrapping process, a Gaussian temperature dependence of the capture cross-sections characterizing the stress-induced traps was introduced. Both the normal and the stress-induced traps have been characterized, including some previously considered as only noise features. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3525582]

A new model for the thermal spike produced by the nuclear energy loss, as source of transient processes, is derived analytically, for power law dependences of the diffusivity on temperature, as solution of the heat equation. The contribution of the ionizing energy loss to the spike is not included. The range of validity of the model is analysed, and the results are compared with numerical solutions obtained in the frame of the previous model of the authors, which takes into account both nuclear and ionization energy losses, as well as the coupling between the two subsystems in crystalline semiconductors. Particular solutions are discussed and the errors induced by these approximations are analysed. (C) 2011 Elsevier B.V. All rights reserved.

One of the clues in detection in modern physics is the development of detector materials able to produce simultaneously two or more different processes, as well as the measurement of the physical quantities associated to these processes in order to discriminate and to identify different particles. In the same time, the absorption of radiation in matter is not a continuous process and due to the interaction mechanism it is localized. As a result, for short time, transient processes are produced, some of them used in detection, other producing disorder that affects the properties of the detector material. In the present paper the thermal spike model is extended and used for semiconductors and liquefied noble gases used as target media for detectors. Both classes of materials are very promising for the detection of heavy particles in nuclear and astroparticle physics.

The long time degradation produced by particles and ions in crystalline materials used for devices to work in space, or for detectors in HEP and astroparticles, is characterised by the non-ionising energy loss, which is calculated in the frame of an analytical model. The transient phenomena as short time degradation are characterised by the time and space dependencies of the lattice and electron temperatures near the projectile trajectory. These processes are considered in the frame of a thermal spike model, which takes into account both ionization and nuclear energy loss processes.

The calorimetric technique is a method used at the present time in several experiments in the search for different forms of dark matter, especially the existence of hypothetical Weakly Interacting Massive Particles or other candidates as neutrino, particles that satisfy the criteria to be non-baryonic, non-luminous and possibly non-relativistic Usually, in several experiments, the simultaneous measurements of the ionization and phonon or light from scintillation signals arc used in the identification of particles Silicon and germanium crystals are used in some experiments, but the energy used in the production of defects in these materials is usually not considered in the energy balance of the processes and could represent a source of errors in particle identification In this paper we investigate the kinetics of defects in cascade interaction processes at cryogenic temperatures, estimate the energetic cost of defect formation in the energy loss and predict the maximal errors in mass and energy identification for WIMPS and neutrinos respectively

The thermal spike model which takes into account both ionization and nuclear energy loss processes of the projectile as distinct electronic and atomic heat sources is used to describe transient processes induced by ions in silicon. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated. The contribution of the rise in temperature on defect formation and annealing is considered.

The temperature dependence of the capture coefficients in trapping phenomena is investigated. It is proved that, besides the dependence induced by the thermal velocity of the carriers, the stress-induced traps at the interfaces of the multi-layered structures present a supplementary temperature dependence. This dependence is found to be of Gaussian type and is in a good agreement with the experimental results.

The thermal spike model developed for the electronic stopping power regime is extended to consider both ionization and nuclear energy loss processes of the projectile as electronic and atomic heat distinct sources. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated and discussed for different ions in silicon, at room and cryogenic temperatures, taking into account the peculiarities of electron-phonon interaction in both domains. The model developed contributes to the understanding of transient microscopic processes immediately after the projectile interaction in the target. (c) 2010 Elsevier B.V. All rights reserved.

The interactions by which ions lose their energy in silicon are investigated at the microscopic level. this theoretical study put in evidence that the ionization could also represent a source of structural defects, and, contrary to the processes initiated by elementary particles, could generate extended primary defects, as, e.g. four-fold coordinated defects, due to the simultaneous breaking of bond for more neighbouring atoms in the lattice in a single interaction, in the ionisation core. The average energy transferred per atom is calculated, and also the energy spent by ionisation. The time dependence of the temperature in the ionisation core is derived in some simplifying assumptions. These contributions not considered yet in the studies of degradation of silicon detectors in radiation fields and could account for the discrepancies observed between models and measurements at microscopic versus device level for hadrons and ions. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this communication, we study the production of defects by energetic ions in silicon and germanium, at very low temperatures, as dependencies of non-ionizing energy loss and number of displacements on the ion kinetic energy, and also the partition of the energy deposited between ionization, creation of defects and phonons, short time after the interaction.

General aspects of the interactions of ions in silicon are investigated: energy lost in electronic and nuclear processes, as well as their consequences, creation of point and extended defects in the crystal structure. The correlations between irradiation ions, their energy, ionization and nuclear energy loss per atom, radius of interaction and spatial extension of the primary damaged region are also investigated.

The knowledge of the effects of radiation in semiconductor devices, in particular in detectors, represents an important and active field of research. The influence of isovalent impurities, carbon and germanium, on the radiation damage of silicon for detectors is investigated in the frame of a quantitative phenomenological model for defect kinetics, developed previously by the authors. The concentrations of defects induced by irradiation in materials with different doping levels are calculated, as well as the leakage current and effective carrier concentrations in p-n junction detectors made from these materials. The beneficial effect of Ge on the radiation damage of silicon is deduced.

The existence of Strange Quark Matter as a new stable or metastable form of existence of matter has been postulated by various authors quite a few years ago. Because until now a theory to predict the existence and the properties of these strangelets does not exist, it is absolutely necessary to investigate the peculiarities of their interactions with matter versus ordinary nuclear matter interactions. In the present contribution, some peculiarities of the ionization and nuclear energy loss of strangelets with matter are investigated in comparison with ordinary ions, as a useful tool for their search. The rescattering mechanism could produce sub-threshold reactions and thus it is suggested as a possibility to discriminate between ordinary isotopes and very heavy (candidates for) strangelets with the same charge number.

The use of semiconductors as detectors for particle and astroparticle physics imposes the understanding of the processes produced in material, their effects on the electronic properties, in their microscopic structure and at the device level. Calculations of LET and NIEL for different ions including hypothetical exotic particles put into evidence the peculiarities of these interactions.

An important tool for the development of devices (detectors, cell solar, electronic circuit components) for high energy accelerator facilities or for space utilization, where new missions and experiments will be operated, is to find new materials with harder radiation properties. The radiation fields in these environments are extremely complex and the tests of the behaviour of different materials and devices for concrete situations are difficult to realise and very expensive. Thus, scaling of degradation effects would represent a useful tool and it is the main aim of the present contribution. Some analytical expressions for NIEL that suggest possible scaling formula are given.

Defects in silicon are studied as function of the dimensionality of the investigated structures. Defects produced by strong irradiation in bulk crystals, like vacancies or interstitial defects, induce other defects, so that the irradiated devices are irreversibly damaged. Defects in nanostructures are shown to be produced mainly by surface/interface states and strains, and are therefore specific to the investigated structure. The modeling of the experimental methods allows the determination of defect parameters that are not directly measurable. The carriers capture on quantum confinement levels in OD systems has a similar behavior with the trapping phenomena.

In this contribution the peculiarities of the behaviour of strange quark matter in respect to ordinary ions in silicon are investigated, and a tentative to identify possible observable effects of degradation is made.

In this contribution, the correlation between fundamental interaction processes induced by radiation in silicon and observable effects which limit the use of silicon detectors in high-energy physics experiments is investigated in the frame of a phenomenological model which includes: generation of primary defects at irradiation, starting from elementary interactions in silicon; kinetics of defects, effects at the p-n junction detector level. The effects due to irradiating particles (pions, protons, neutrons), to their flux, to the anisotropy of the threshold energy in silicon, to the impurity concentrations and resistivity of the starting material are investigated as time, fluence and temperature dependences of detector characteristics. The expected degradation of the electrical parameters of detectors in the complex hadron background fields at LHC & SLHC is predicted. (C) 2007 Elsevier B.V. All rights reserved.

In the present paper, we intend to bring some clarifications related to the role played by primary defects in long term degradation, to the dependence of degradation on the orientation of the wafer, as well as on the spatial distribution of the degradation produced by low energy particle irradiation.

Silicon detectors will be used in the next generation of experiments in high energy physics and bulk damage is the main limitation in their utilisation. Although silicon is the most studied semiconductor, and the studies of defects in silicon have a long history, until now it is not completely established what are all primary defects in silicon, and what are their properties. In this contribution we investigate the new perspective in understanding fundamental phenomena in silicon and implications for the damage of detector characteristics due to the existence of the new primary fourfold coordinated defect, with a lower value of the formation energy in respect to the "classically" known vacancies and interstitials. The effects of its existence at device level are investigated, and possible consequences for the detectors in the next generation of experiments are discussed.

In this contribution, the structural modifications of the material and the degradation of devices is modelled and compared with the experimental data for more resistivities, temperatures, crystal orientations and oxygen concentrations, considering the existence of the new primary fourfold coordinated defect, besides the vacancy and the interstitial. Some estimations of the behaviour of detectors in specific environments at the next generations of high-energy physics experiments as LHC, SLHC, VLHC, or ULHC are done. (c) 2006 Elsevier B.V. All rights reserved.

The irradiation represents a useful tool for determining the characteristics of defects in semiconductors as well as a method to evaluate their degradation, a fact with important technological consequences. In this contribution, starting from available data on the degradation of silicon detector characteristics in radiation fields, these effects are explained in the frame of a model that supposes also the production of the Si-FFCD defect due to irradiation. The displacement threshold energies different for different crystallographic axes, considered as parameters of the model, are established and the results obtained could contribute to clarify these controversial aspects. Predictions of the degradation of electrical parameters (leakage current, effective carrier concentration and effective trapping probabilities for electrons and holes) of DOFZ silicon detectors in the hadron background of the LHC accelerator, supposing operation at -10 degrees C, are done. The non-uniformity of the rate of production of primary defects and of complexes, as a function of depth, for incident particles with low kinetic energy was obtained by simulations using some particular and very simplifying assumptions, suggesting the possible important contribution of the low-energy component of the background spectra to detector degradation. (c) 2007 Elsevier B.V. All rights reserved.

In this contribution, an extensive analysis of the primary defects in silicon: vacancy, interstitial and Si-FFCD is performed. Irradiation studies are a useful tool to study production, characteristics and annealing of defects. The experimental results obtained after high proton fluence irradiation of silicon detectors are used in this paper to understand aspects related to the existence and proprieties of primary defects. Investigations on possible differences induced by irradiation in the lattice of silicon, using transmission electron microscopy analysis, have been started and some first preliminary results are presented.

The principal obstacle to long-time operation of silicon detectors at the highest energies in the next generation of experiments arises from bulk displacement damage which causes significant degradation of their macroscopic properties. The analysis of the behaviour of silicon detectors after irradiation conduces to a good or reasonable agreement between theoretical calculations and experimental data for the time evolution of the leakage current and effective carrier concentration after lepton and gamma irradiation and large discrepancies after hadron irradiation and this in conditions where a reasonable agreement is obtained between experimental and calculated concentrations of complex defects. In this paper, we argue that the main discrepancies could be solved naturally considering as primary defects the self-interstitials, classical vacancies and the new predicted fourfold coordinated silicon pseudo-vacancy defects. This new defect is supposed to be introduced uniformly in the bulk during irradiation, has deep energy level(s) in the gap and it is stable in time. Considering the mechanisms of production of defects and their kinetics, it was possible to determine indirectly the characteristics of the Si-FFCD defect: energy level in the band gap and cross-section for minority carrier capture. In the frame of the model, the effects of primary defects on the degradation of silicon detectors are important in conditions of continuous long-time irradiation and/or high fluences.

The proposed luminosity upgrade of the Large Hadron Collider (S-LHC) at CERN will demand the innermost layers of the vertex detectors to sustain fluences of about 10(16) hadrons/cm(2). Due to the high multiplicity of tracks, the required spatial resolution and the extremely harsh radiation field new detector concepts and semiconductor materials have to be explored for a possible solution of this challenge. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has started in 2002 an R&D program for the development of detector technologies that will fulfill the requirements of the S-LHC. Different strategies are followed by RD50 to improve the radiation tolerance. These include the development of defect engineered silicon like Czochralski, epitaxial and oxygen-enriched silicon and of other semiconductor materials like SiC and GaN as well as extensive studies of the microscopic defects responsible for the degradation of irradiated sensors. Further, with 3D, Semi-3D and thin devices new detector concepts have been evaluated. These and other recent advancements of the RD50 collaboration are presented and discussed. (c) 2005 Elsevier B.V. All rights reserved.

An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work. 2005 Published by Elsevier B.V.

The envisaged upgrade of the Large Hadron Collider (LHC) at CERN towards the Super-LHC (SLHC) with a 10 times increased luminosity of 10(35) cm(-2) s(-1) Will present severe challenges for the tracking detectors of the SLHC experiments. Unprecedented high radiation levels and track densities and a reduced bunch crossing time in the order of 10 ns as well as the need for cost effective detectors have called for an intensive R&D program. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" is working on the development of semiconductor sensors matching the requirements of the SLHC. Sensors based on defect engineered silicon like Czochralski, epitaxial and oxygen enriched silicon have been developed. With 3D, Semi-3D and thin detectors new detector concepts have been evaluated and a study on the use of standard and oxygen enriched p-type silicon detectors revealed a promising approach for radiation tolerant cost effective devices. These and other most recent advancements of the RD50 collaboration are presented. (c) 2005 Elsevier B.V. All rights reserved.

The influence of oxygen and carbon impurities on the concentrations of defects in silicon for detector uses, in complex fields of radiation, characteristic to high energy physics experiments, is investigated in the frame of the quantitative phenomenological model developed previously by the authors and extended in the present paper. Continuous irradiation conditions are considered, simulating realistically the environments for these experiments. The generation rate of primary defects is calculated starting from the projectile-silicon interaction and from the recoil energy redistribution in the lattice. The mechanisms of formation of complex defects are explicitly analysed. Vacancy-interstitial annihilation, interstitial and vacancy migration to sinks, divacancy, vacancy- and interstitial-impurity complex formation and decomposition are considered. Oxygen and carbon impurities present in silicon could monitor the concentration of all stable defects, due to their interaction with vacancies and interstitials. Their role in the mechanisms of formation and decomposition of the following stable defects: V-2, VO. V2O, C-i, CiOi, CiCs, and VP, is studied. The model predictions cover a generation rate of primary defects between 10(2) pairs/cm(3)/s and 10(11) pairs/cm(3)/s, and could be a useful clue in obtaining harder materials for detectors for space missions, at the new generation of accelerators, as, e.g. LHC, Super-LHC and Eloisatron, or for industrial applications.

Silicon detectors represent an important option for the Large Hadron Collider and for its upgrades in luminosity and energy, especially for the tracking system. The main limitation in their utilisation comes from the degradation in the hostile radiation environment where they, will work for long time, without the possibility to be changed. The main goal of this paper is to study, the role of growth technology on stable defect concentrations produced by long-time continuous irradiation in the radiation field estimated for LHC and SLHC.

The influence of oxygen and carbon impurities on the concentrations of defects in silicon for detector uses, in complex fields of radiation (proton cosmic field at low orbits around the Earth, at Large Hadron Collider and at the next generation of accelerators as Super-LHC) is investigated in the frame of the quantitative model developed previously by the authors. The generation rate of primary defects is calculated starting from the projectile - silicon interaction and from recoil energy redistribution in the lattice. The mechanisms of formation of complex defects are explicitly analysed. Vacancy-interstitial annihilation, interstitial and vacancy migration to sinks, divacancy, vacancy and interstitial impurity complex formation and decomposition are considered. Oxygen and carbon impurities present in silicon could monitor the concentration of all stable defects, due to their interaction with vacancies and interstitials. Their role in the mechanisms of formation and decomposition of the following stable defects: VP, VO, V-2, V2O, C-i, CiOi and CiCs is studied. The model predictions could be a useful clue in obtaining harder materials for detectors at the new generation of accelerators, for space missions or for industrial applications.

Silicon detectors in particle physics experiments at the new accelerators or in space missions for physics goals will be exposed to extreme radiation conditions. The principal obstacles to long-term operation in these environments are the changes in detector parameters, consequence of the modifications in material properties after irradiation. The phenomenological model developed in the present paper is able to explain quantitatively, without free parameters, the production of primary defects in silicon after particle irradiation and their evolution toward equilibrium, for a large range of generation rates of primary defects. Vacancy-interstitial annihilation, interstitial migration to sinks, divacancy and vacancy-impurity complex (VP, VO, V2O and CiOi, CiCs) formation are taken into account. The effects of different initial impurity concentrations of phosphorus, oxygen and carbon, as well as of irradiation conditions are systematically studied. The correlation between the rate of defect production, the temperature and the time evolution of defect concentrations is also investigated. (C) 2002 Elsevier Science B.V. All rights reserved.

In the present paper. the phenomenological model developed by the authors in previous papers has been used to evaluate the degradation induced by hadron irradiation at future accelerator facilities or by cosmic protons in high resistivity silicon detectors. The damage has been analysed at the microscopic (defects production and their evolution toward equilibrium) and at the macroscopic level (changes in the leakage current of the p-n junction). The rates of production of primary defects. its well as their evolution toward equilibrium have been evaluated considering explicitly the type of projectile particle and its energy. Vacancy-interstitial annihilation. interstitial migration to sink. divacancy and complex (VP, VO, V2O, CiOi, CiCs) formation are taken into account for differently doped initial silicon material. The influence of these defects on the leakage current density has been compared with experimental data from the literature, and predictions for the LHC (Large Hadron Collider) radiation fields. as well as for space missions in the near Earth orbits have been done. in the frame of the Schokley-Read-Hall model.

In this contribution, the production of defects in radiation fields and their evolution toward equilibrium in silicon for detector uses has been modelled. In the quantitative model developed, the generation rate of primary defects is calculated starting from the projectile-silicon interaction and from recoil energy redistribution in the lattice. Vacancy-interstitial annihilation, interstitial migration to sinks, divacancy and vacancy-impurity complex (VP, VO, V2O, CiOi and CiCs) formation are considered. The results of the model support the experimental available data. The correlation between the initial material parameters, temperature, irradiation and annealing history is established. The model predictions could be a useful clue in obtaining harder materials for detectors at the new generation of accelerators or for space missions. (C) 2003 Elsevier B.V. All rights reserved.

A phenomenological model was developed to explain quantitatively, without free parameters, the production of primary defects in silicon after particle irradiation, the kinetics of their evolution toward equilibrium and their influence on detector parameters. The type of the projectile particle and its energy is considered in the evaluation of the concentration of primary defects. Vacancy-interstitial annihilation, interstitial migration to sinks, vacancy-impurity complexes (VP, VO, V2O), and divacancy (V-2) formation are taken into account in different irradiation conditions, for different concentrations of impurities in the semiconductor material, for 20 and 0degreesC. The model can be extended to include other vacancy and interstitial complexes. The density of the reverse current in the detector after irradiation is estimated. Comparison with experimental measurements is performed. A special application considered in the paper is the modelled case of the behaviour of silicon detectors operating in the pion field estimated for the LHC accelerator, under continuum generation and annealing.

In the present work, the bulk degradation of SiC in hadron (pion and proton) fields, in the energy range between 100 MeV and 10 GeV. is characterised theoretically by means of the concentration of primary defects per unit fluence. The results are compared to the similar ones corresponding to diamond, silicon and GaAs. (C) 2001 Elsevier Science B.V. All rights reserved.

Based on the general Lindhard theory describing the partitioning of particles' energy in materials between ionisation and displacements, approximate analytical solutions have been derived, for media containing one and more atomic species, for particles identical and different from the medium ones. Particular cases, and the limits of these equations at very high energies are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

The concentration of primary radiation-induced defects has been previously estimated considering both the explicit mechanisms of the primary interaction between the incoming particle and the nuclei of the semiconductor lattice., and the recoil energy partition between ionisation and displacements, in the frame of the Lindhard theory. The primary displacement defects are vacancies and interstitials that are essentially unstable in silicon. They interact via migration, recombination, annihilation or produce other defects. In the present work, the time evolution of the concentration of defects induced by pions in medium and high resistivity silicon for detectors is modelled, after irradiation, In some approximations, the differential equations representing the time evolution processes could be decoupled. The theoretical equations so obtained are solved analytically in some particular cases. with one free parameter, for a wide range of particle fluences and/or for a wide energy range of incident particles, for different temperatures; the corresponding stationary solutions are also presented. (C) 2001 Elsevier Science B.V. All rights reserved.

Anodic film oxide was deposited in a alcohol-glycol-water (AGW) solution on n-GaAs for passivation purpose in stripe technology for laser diodes. The characteristics of anodic oxide were measured by scanning electron microscopy (SEM), Rutherford backscattering (RBS) analysis and elastic recoil detection (ERD) techniques. The result indicates a complex oxide structure in the phase base Ga2O3:As2O3 (1:1) joint together with carbon bonds. Due to the presence of carbon in anodic oxide, laser diodes are exposed to rapid degradation during operation.

Trapping levels in fresh (one month) and naturally aged (one year) nanocrystalline porous silicon have been investigated using the optical charging spectroscopy method. Four significant maxima and/or shoulders were observed for fresh samples and five for aged ones. They have been attributed to five and six trapping levels, respectively. The trapping centers corresponding to the most shallow four levels are situated at or nearby the internal surface of the porous silicon films. (C) 2000 American Institute of Physics. [S0003-6951(00)01621-1].

Two sets of p-type silicon thigh resistivity bulk and low resistivity epitaxial) samples and one set of n(+)-p junctions have been irradiated with fast neutrons up to 8 x 10(13) cm(-2). I-V and C-V characteristics as well as Thermally Stimulated Currents (TSC) and Hall Effect (HE) analyses have been performed on the irradiated samples and diodes in view to determine the radiation-induced damage and the change in the electrical properties. A change in the effective carrier concentration and in the leakage current after irradiation similar to the one found for p(+)-n detectors has been observed in p-type diodes. An increase with the fluence of the resistivity and Hall coefficient was measured at room temperature both for the low and high resistivity sets. This evidence has been explained in terms of a two-level model taking into account a linear increase in concentration with the fluence of the main radiation-induced defects observed with TSC, probably related to divacancy and carbon-oxygen complex. (C) 1999 Elsevier Science B.V. All rights reserved.

The changes induced by neutron irradiation in n- and p-type silicon samples with starting resistivities from 10 Omega-cm up to 30 K Omega-cm, grown, using different techniques, as Float-Zone (FZ), Czochralski (CZ) and epitaxial, have been analyzed by Van der Pauw and Hall effect measurements. Increasing the fluence, each set of samples evolves toward a quasi-intrinsic p-type material. This behavior has been explained in the frame of a two-level model, that considers the introduction during irradiation of mainly two defects. A deep acceptor and a deep donor,probably related to the divacancy and to the CiOi complex, are placed in the upper and lower half of the forbidden gap, respectively. This simple model explains quantitatively the data on resistivity and Hall coefficient of each set of samples up to the fluence of approximate to 10(14) n/cm(2).

The energy dependence of the concentration of primary displacements induced by protons and pions in diamond has been calculated in the energy range 50 MeV - 50 GeV, in the frame of the Lindhard theory. The concentrations of primary displacements induced by protons and pions have completely different energy dependencies: the proton degradation is very important at low energies, and is higher than the pion one in the whole energy range investigated, with the exception of the Delta(33) resonance region. Diamond has been found, theoretically, to be one order of magnitude more resistant to proton and pion irradiation in respect to silicon.

A comparative theoretical study of the damages produced by protons and pions, in the energy range 50 MeV-50 GeV, in diamond, is presented. The concentration of primary defects (CPD) induced by hadron irradiation is used to describe material degradation. The CPD has very different behaviours for protons and pions: the proton degradation is important at low energies and is higher than the pion one in the whole energy range investigated, with the exception of the Delta(33) resonance region, where a large maximum of the degradation exists for pions. In comparison with silicon, the most investigated and the most utilised semiconductor material for detectors, diamond theoretically proves to be one order of magnitude more resistant both to proton and pion irradiation. (C) 1999 Elsevier Science B.V. All rights reserved.

High power laser diodes are of interest due to their potential use in medicine and military applications. This paper presents a systematic study of rapid degradation on our AlGaAs/GaAs large optical cavity devices. The increase of normalized threshold current vs. time was experimentally studied. An evaluation for normalized threshold current vs. absorption coefficient for different reflectivities is presented. For the optical output vs. time curve an abnormal increase of light characteristics was experimentally observed. The variation of the optical power was correlated to material parameters during operation and this behavior has been proposed as a practical criterion to select devices that are on their route to rapid degradation. The output optical power vs. electron fluence curve was measured for irradiated devices and a dislocation climb motion was assumed.

A theoretical study of the radiation effects, from the point of view of the non-ionising energy loss and of the concentration of primary defects, in some A(3)B(5) semiconductors, has been performed. These effects have been analysed for charged pions, in the energy range 50 MeV-50 GeV. The investigated materials have been GaAs, InP, GaP, InAs and InSb, and the results have been compared with silicon, as a reference material, keeping into account the peculiarities of the pion-nucleus interaction, and the recoil energy redistribution in the lattice. The results of the calculations have put in evidence the higher radiation resistance of Si, GaP and GaAs in the whole energy range investigated, with respect to the other analysed materials: InP, InAs and InSb, that proved to be of interest from this point of view only in the intermediate energy region. (C) 1998 Elsevier Science B.V. All rights reserved.

We have measured I-V and C-V characteristics, the temperature dependence of dark currents, and thermally stimulated depolarisation currents on fresh and stored samples of photoluminescent porous silicon, By storage in ambient, the low rectifying I-V curves become strong rectifying, and C-V curves become MIS-like. I-T characteristics for fresh samples have only one activation energy, in the 0.49-0.55 eV range. After storage, a slightly modified value, of about 0.50-0.60 eV is observed at low temperatures only. At about 280 K, the activation energy suddenly changes to 1.20-1.80 eV. Also, both the number and the positions of maxima in thermally stimulated depolarisation currents change by storage. The annealing at about 50 degrees C induces small reversible changes in I-T characteristics and strong irreversible ones in thermally stimulated depolarisation currents, both for fresh and stored samples. A simplified quantum confinement model is proposed to explain the main aspects of the electrical behaviour of porous silicon films. The surface and/or interface contributions are observed especially in thermally stimulated depolarisation currents. The changes induced by storage are attributed to the oxidation process of the internal surface of porous silicon films. (C) 1998 Elsevier Science S.A. All rights reserved.

The non-ionising energy loss and the concentration of primary radiation defects induced by charged pions, in the energy range 50-500 MeV, in bulk diamond have been calculated in order to characterise its radiation resistance. The mechanisms by which the pion imparts energy to the diamond lattice have been analysed and their contribution has been evaluated starting from the nuclear data on pion-carbon interaction. The energy partition of the primary recoil nuclei between ionisation and displacements has been calculated in the frame of the Lindhard theory. It has been found that diamond, from the point of view of concentration of primary defects, is approximately one order of magnitude harder than silicon in pion fields, in the energy range of the Delta(33) resonance, and about two orders of magnitude harder than GaAs in the same energy region. (C) 1998 Elsevier Science B.V. All rights reserved.

The concentration of primary radiation defects induced by charged pions, in the energy range 20 MeV-50 GeV, in the bulk of silicon, GaAs and diamond has been calculated in order to characterise the radiation resistance of these materials. The mechanisms by which pions impart energy to the lattice have been analysed and their contribution has been evaluated starting from the data on pion-nucleus interaction. The energy partition of the primary recoil nuclei between ionisation and displacements has been considered in the frame of the Lindhard theory. The energy dependence of the concentration of primary radiation defects presents two maxima: one in the region of the delta resonance, and another one around 1 GeV. The main conclusion is that diamond is hardner to pion irradiation than both silicon and GaAs in the whole energy range investigated. The pion-induced degradation in the inner detector system at LHC has been evaluated, starting from the simulated spectra, and considering different detector materials: diamond, silicon and GaAs. (C) 1998 Elsevier Science B.V. All rights reserved.

The dependence of the displacement damage induced by pions in GaAs has been evaluated, in the energy range 50 -1000 MeV, using the Lindhard theory and parametrised values of the pion-nucleus interaction. The curves corresponding to the NIEL produced by protons, neutrons, and pions in Si and in GaAs intersect, in the limit of calculation errors, in the region 50 - 80 MeV, at a NIEL of 2 - 5.5 MeV cm(2)/g. The energy dependence of the NIEL of pions in Si and GaAs is discussed in correlation with the simulated pion spectra at new hadron colliders.

The dependence of the displacement damage induced by pions in silicon has been calculated as a function of their kinetic energy, between 50 and 1000 MeV, using data on pion-silicon interaction. The region of the delta resonance has been carefully considered. because it corresponds to a sharp maximum in the spectra of simulated pion production in the central cavity of LHC. Results are reported on previous calculations and on experimental damage data measured in silicon detectors irradiated with pions.

The concept of NIEL (Non Ionising Energy Loss) is usually considered to correlate the effects of the displacement damage produced in the material bulk by different particles in different energy ranges. An evaluation of the NIEL is especially important for those semiconductors which are planned to be used in the extreme radiation environment of the new generation of colliders as LHC. In the present work, a calculation of the pion NIEL in silicon and GaAs, in the energy region up to 50 GeV is reported and discussed. The energy dependence of the NIEL is found to follow the resonant structures of the pion-nuclei interactions, where the strongest effect is due to the Delta(33) resonance. Above 1 GeV a slight monotonic decreasing behaviour of the NIEL has been found, both for Si and GaAs.

The electrical transport of stabilised porous silicon layers was investigated. The samples were stored in ambient for 1,5-2 years, A MIS-like C-V characteristic, a strong rectifying I-V curve and I-T dependence with two activation energies were obtained, Thermally stimulated depolarization currents have an activation energy of 0.81-0.87 eV. The electrical properties are discussed in the frame of a quantum confinement model, keeping into account the surface component.

Four contact bulk samples and p(+)n junction diodes produced from high resistivity n-type silicon wafers of the same ingot have been irradiated with 1 MeV-neutron fluences between 10(12) and 3 x 10(13) cm(-2). The effective impurity concentration N-eff has been calculated from CV measurements in irradiated diodes, and bulk resistivity has been measured with the Van der Pauw method on four contact samples. The experimental resistivity and N-eff dependence on the irradiation fluence, self-annealing time and storage temperature have been modeled considering the exponential shallow donor decay and the creation of acceptor traps in the irradiated silicon. A numerical fit to the experimental data, based on the solution of the neutrality and Poisson equations, has been carried out considering an equivalent deep acceptor defect created during and after irradiation in the silicon lattice. The energy level and the introduction rate of this defect, evaluated as best-fit parameters in the numerical procedure, are E-t = 0.60-0.65 eV above the valence band edge and b similar to 0.06 cm(-1).

Bulk samples obtained from two wafers of a silicon monocrystal material produced by float-zone refinement have been analysed using the four-point probe method. One of the two wafers comes from an oxygenated ingot; two sets of pure and oxygenated samples have been irradiated with 24 GeV/c protons in the fluence range from 10(13) to 1.74 x 10(14) p/cm(2). Van der Pauw resistivity and Hall coefficient have been measured before and after irradiation as a function of the temperature. A thermal treatment (30 min at 100 degrees C) has been performed to accelerate the reverse annealing effect in the irradiated silicon. The irradiated samples show the same exponential dependence of the resistivity and of the Hall coefficient on the temperature corresponding to the presence of radiation-induced deep energy levels around 0.6-0.7 eV in the silicon gap. The free carrier concentrations (n, p) have been evaluated in the investigated fluence range. The inversion of the conductivity type from n to p occurred, respectively, at 7 x 10(13) and at 4 x 10(13) p/cm(2) before and after the annealing treatment for both the two sets. Only slight differences have been detected between the pure and the oxygenated samples.

The dependence of the carrier concentrations, of the resistivity and of the Hall coefficient of irradiated silicon on the neutron fluence has been investigated, starting from the supposition that the main phenomena induced by irradiation in the semiconductor bulk are shallow-donor removal and deep-centres creation. The free parameters of the model are the initial doping of the starting material, the permitted energy level values of the radiation-induced centres in the semiconductor band gap and their introduction rates. The influence of each parameter on the calculated dependences is studied in detail, for three cases: one deep acceptor-like centre, two deep accepters and one deep acceptor plus one deep donor-like centre. Each of the three cases is discussed in correspondence with different experimental results.

High resistivity n-type silicon samples have been irradiated with similar to 1MeV neutrons at fluences between 10(12) and 10(14) n/cm(-2). The radiation induced changes in Hall coefficient and resistivity have been analysed by Hall Effect measurement during a storage time of approximately seven months at room temperature. The Hall coefficient measured for the most irradiated samples, exposed to fluences higher than 4x10(13) cm(-2), has switched from negative to positive values approximately 200 days after the irradiation. This experimental evidence explains the reverse annealing effect observed in neutron irradiated silicon detectors as being related to the creation of a deep acceptor level which causes the change in conductivity from n to p-type of the irradiated silicon bulk during self annealing. The behaviour of irradiated devices has been analyzed with a model taking into account donor removal and acceptor creation. Results are in agreement with others obtained with different experimental techniques.