National Institute Of Materials Physics - Romania

Gain-layer degradation from exposure to radiation limits the use of Low-Gain Avalanche Diodes (LGADs) in high energy particle physics detector experiments. Proper understanding of how the gain-layer is altered is not available on a defect level. Only measurements for materials with much lower effective doping concentrations are available. The direct study of the gain-layer is not possible with typical defect spectroscopy measurements like Thermally Stimulated Currents (TSC) and Deep-Level Transient Spectroscopy (DLTS). To combat this problem and gain a better understanding of the processes which degrade LGADs, the Gain-Layer Project was started. Within this project 19050 diodes were produced with various Boron, Phosphorus, Oxygen and Carbon concentrations. The material used is low-resistivity p-type Silicon. The effective doping concentrations are in the order of typical LGAD gain-layers. These diodes will serve the defect community in the coming years for various studies. This article introduces this project with detailed descriptions of the diodes, their flavours and their processing, and reports on results from I-V, C-V, SIMS and DLTS measurements on unirradiated diodes.

This work presents a comprehensive investigation of the structural, microstructural, magnetic, and magneto-caloric properties of La0.9-xPbxNa0.1MnO3 (x = 0 and 0.1), synthesized through a flash combustion technique and subsequently pressed into pellets. Structural analysis confirms that both samples crystallize in a rhombohedral structure without detectable secondary phases or impurities. Microstructural observations reveal a homogeneous morphology in both compositions, with a noticeable grain growth effect induced by Pb doping. Magnetic measurements show a clear paramagnetic-ferromagnetic phase transition in both samples. The Curie temperature shifts from 179 K for the undoped compound to 309 K for the Pb-doped compounds. Furthermore, the magnetic entropy change and the relative cooling power increase from 3.01 J/kg.K and 184.72 J/kg for La0.9Na0.1MnO3 to 4.56 J/kg.K and 291.29 J/kg for La0.8Pb0.1Na0.1MnO3. Together, these results highlight the beneficial effect of Pb doping in the studied system for room-temperature magnetic refrigeration applications.

Optimizing the interfaces in perovskite solar cells (PSCs) is essential for enhancing their performance, improving their stability, and making them commercially viable for large-scale deployment in solar energy harvesting applications. Point defects, like vacancies, have a dual role, as they can inherently provide a proper doping, but they can also reduce the collected current by trap-assisted recombination. Moreover, they can play an active role in ion migration and degradation. Using ab initio density functional theory calculations we investigate the changes in the band alignment induced by interfacial vacancy defects in a TiO 2/MAPI/Cu 2O based PSC. Depending on the type of the vacancy (Ti, Cu, O, Pb, I) in the oxide and perovskite materials, additional doping is superimposed on the already existing background. Their effect on the performance of the PSCs becomes visible, as shown by SCAPS simulations. The most significant impact is observed for p type doping of TiO 2 and n type doping of Cu 2O, while the effective doping of the perovskite layer affects one of the two interfaces. We discuss these results based on modifications of the band structure near the active interfaces and provide further insights concerning the optimization of electron and hole collection.

The aggressive scaling of electronic devices has brought ferroelectric materials to the forefront of nanoscale research, where lateral dimensions strongly influence switching dynamics and device performance. In this context, W/ Hf0.5Zr0.5O2/ p-Ge capacitors with top electrode sizes ranging from 10 & micro;m down to 0.1 & micro;m are investigated using conductive atomic force microscopy (C-AFM). Frequency-dependent measurements reveal that peak switching currents (Isw) increase with sweep rate, yet the total switched charge remains nearly constant, consistent with full polarization reversal in micro- and submicron devices. Positive-Up-Negative-Down (PUND) analysis further isolates the switching current, allowing reconstruction of polarization-voltage (P--V) loops and quantification of remnant polarization. The smallest devices (0.01 & micro;m2) exhibit switching currents below the detection threshold due to parasitic capacitance, masking intrinsic ferroelectric behavior. In contrast, submicron capacitors display an apparent increase of remanent polarization attributed to the larger perimeter-to-area ratio, emphasizing the role of edge-dominated switching. Together, these findings establish C-AFM as a powerful, spatially resolved technique for probing ferroelectric switching in realistic device geometries, providing essential insights for non-volatile memory and neuromorphic applications.

This study synthesized a solid-solution series of KCo1-x Ni x Cr2(PO4)3 phosphates with the alpha-CrPO4-type three-dimensional framework, in which edge-sharing CrO6 octahedra and PO4 tetrahedra create tunnels hosting K+ cations. Systematic Ni2+/Co2+ substitution was used to tune dielectric and charge-transport properties. All compounds showed stable paraelectric behavior; increasing Co content enhanced polarizability and dielectric permittivity while maintaining low dielectric loss. When used as electrode materials in graphite-based supercapacitors, higher Co content led to improved electrochemical performance, with the Co1Ni0 composition delivering a specific capacitance of 447 F/g, an energy density of 48.18 Wh/kg, and a power density of 1752 W/kg. The results demonstrate that Ni2+/Co2+ substitution is an effective strategy for designing advanced supercapacitor electrodes that combine high charge-storage capacity (due to increased permittivity) with improved power capability (due to higher conductivity).

Co-/Cu-co-doped ZnO nanorods are synthesized by electrochemical deposition to investigate the effect of co-doping on their structural, optical, electronic, and electrochemical properties. XRD, Raman, SEM, and photoluminescence analyses reveal that Co/Cu incorporation modifies the ZnO lattice, increases defect-related states, and reduces the band gap from 3.11 to 2.15 eV. Density functional theory calculations further show that Co 3d and Cu 3d states appear near the Fermi level and contribute to the observed band-gap narrowing. Electrochemical measurements indicate that the co-doped nanorods exhibit the lowest charge-transfer resistance and the highest areal capacitance among the samples studied. Together, these results show that Co/Cu co-doping improves charge-transfer kinetics in ZnO nanorods and highlights co-doping as an effective strategy for tuning oxide electrodes for energy-storage applications.

In this work, Cu2Zn1-xNixSnS4 (CZ1-xNixTS) thin films were successfully synthesized via the solution-based spin-coating technique, and the effects of partial substitution of Zn by Ni (x = 0.2, 0.4, and 0.6) on their structural, morphological, optical, and photovoltaic properties were systematically investigated. Structural analyses demonstrated that Ni substitution in CZTS leads to lattice contraction and partial structural distortion due to the smaller ionic radius of Ni2+. Increasing Ni content enhances these effects until a solubility limit is reached at x approximate to 0.6, beyond which secondary phases such as NiS and Cu2SnS3 emerge. Raman spectroscopy further supports these findings, indicating compositional inhomogeneity and phase segregation at high Ni concentrations. Scanning Electron Microscope (SEM) micrographs further show that moderate Ni incorporation (x = 0.2) promotes improved surface compactness and grain growth, while excessive substitution results in grain fragmentation and increased surface roughness. Optical characterization reveals a tunable band gap, decreasing from 1.42 eV (x = 0) to 1.08 eV (x = 0.2), followed by a slight increase at higher doping levels, consistent with the formation of secondary phases. SCAPS-1D simulations of Mo/C2Z1-xNixSnS4/CdS/ZnO:Al/Al solar cell structures indicate improved photo-generated current and optical absorption at x = 0.2, whereas higher Ni substitution reduces the open circuit voltage (Voc) and the fill factor FF due to increased carrier recombination. Overall, moderate Ni incorporation enhances light absorption and carrier transport, whereas excessive Ni incorporation induces structural disorder, degrading device performance. These findings contribute to understanding the structural and compositional stability of Ni-doped CZTS thin films and their optimization for solar energy applications.

Copper-zinc-tin-sulfide (Cu2ZnSnS4, CZTS) kesterites a promising earth-abundant and non-toxic absorber for next-generation thin-film photovoltaics. However, sulfur-based CZTS solar cells remain limited in performance, largely due to intrinsic defects and interfacial recombination losses. Here, we systematically investigate the impact of solvent chemistry and extrinsic doping and compositional engineering on the quality of solution-processed CZTS absorbers. A comparative study of three solvents, 2-methoxyethanol (MOE), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) reveals that all yield phase-pure, and compact films due to a robust Cu+-Sn4+ molecular precursor system, with MOE producing the most uniform morphology and superior optoelectronic properties. Rather than focusing on pure CZTS, the solvent screening is conducted on Cd-alloyed CZTS (CZCTS), as Cd incorporation substantially alters precursor coordination and crystallization behavior. Building on the optimized processing route, a synergistic compositional strategy combining silver (Ag) - cadmium (Cd) co-alloying with lithium (Li) doping is introduced to suppress cation disorder, passivate grain-boundary defects, and enhance carrier transport. As a result, the optimized he optimized absorber delivers a champion device with a power conversion efficiency of 10.6%, placing it among the highest efficiencies reported for solution-processed, selenium-free CZTS solar cells. These results highlight the critical role of solvent engineering coupled with targeted extrinsic doping in overcoming the long-standing limitations of CZTS photovoltaics and provide a scalable pathway toward environmentally benign thin-film solar technologies.

The glass/FTO/TiO2/Sb2S3-x/P3HT/Au solar cells were investigated, with a focus on identifying the origin of performance degradation after exposure to high relative humidity and to mild heat stress. Analyzing the photovoltaic output and Deep-Level Transient Spectroscopy (DLTS) results, we probed the evolution of defect states after thermal exposure and after long-term storage of Sb2S3-x-based devices. The DLTS analysis revealed that shallow hole traps govern the stability of the Sb2S3-x cells. Significantly, it was shown that this shallow defect is not related to chlorine in the absorber, indicating an intrinsic origin. In the broader context of Sb2S3-x photovoltaics, this study underlines the paramount importance of defect engineering towards achieving more stable and efficient Sb2S3-x solar cells.

Magnetic superconductor EuRbFe4As4 is a quite unique system in which macroscopic superconductivity and magnetic ordering coexist, with interesting interactions between Abrikosov vortices and Eu2+ spins that were investigated mostly by static (DC) magnetization measurements. Our aim is to study the dynamic interactions between the two sub-systems using AC susceptibility measurements in a wide range of temperatures and superimposed DC fields. In low DC fields, the magnetic transition at 15 K is clearly visible. We have observed very little difference between the AC susceptibility in different cooling regimes, but large difference for different field orientation. For field perpendicular to the superconducting planes, we have observed an anomalous dependence just below the critical temperature, which is absent in the parallel field orientation. We explained the anomaly by the interplay between the sample dimensions and the temperature dependence of the London penetration depth which may allow the paramagnetic Meissner-like response to be detected in the temperature dependence of the AC susceptibility. We stress that the newly reported phenomenon reflects an AC-susceptibility manifestation of a field-stabilized critical state rather than a thermodynamic phase. In addition, we have observed a paramagnetic AC response in the normal phase, in both field orientations, indicative of interactions between Eu2+ spins and flux lines.