Dr. Ionel Stavarache

Dr. Ana-Maria Lepadatu

Dr. Catalin Palade

Dr. Ioana-Maria Avram Dascalescu

Dr. Adrian Slav

Drd. Mihalcea Catalina-Gabriela

Dr. Catalin Negrila

Drd. Ovidiu Cojocaru

Stage I/2022

In the Stage I/2022, photodetector structures based on GeSnSi3N4 films in which the Sn concentration in the film was varied between ~4%vol. and ~ 18 %vol. were made. The films were deposited by magnetron sputtering on Si and quartz substrate maintained at room temperature during deposition.

The formation of GeSn nanocrystals/dots in GeSnSi3N4 films was achieved by thermal annealing RTA, after optimizing the necessary parameters, namely temperatures in the range of 325 - 700 °C.

The morphology and structure of the investigated films are strongly dependent on the Sn concentration in the GeSnSi3N4 films. In the amorphous films with increased Sn concentration, the structure is more dilated in the sense that the distance between the atoms in the first coordination sphere and the second coordination sphere is increased. This phenomenon also occurs in crystallized GeSn, i.e. the lattice constant increases with the increase in Sn concentration.

Optical investigations highlight the influence of the Sn concentration in the films on the absorption threshold. In the films where the Sn concentration is approximately 18 %vol, the absorption threshold has a value of 0.5 eV compared to the value of 0.7 eV corresponding to a Sn concentration of ~4 %vol.

The I – V characteristics obtained on GeSnSi3N4 / Si films show that the photocurrent is 4 orders of magnitude higher than the dark current and is strongly dependent on the measurement temperature. In addition, the spectral dependence of the photocurrent on these films presents a wide sensitivity band, in the range 520 - 1750 nm. The obtained results from the optical investigations are in agreement with the spectral ones and demonstrate that these films have adequate photoconductive properties for the manufacture of photodetectors.

In conclusion, the objectives and activities proposed for Stage I/2022 were fully achieved.

Stage II/2023

In Stage II/2023, GeSnSi3N4-based photodetector structures were produced in which the Sn concentration in the film was varied between ~4 %vol. and ~ 18 %vol. The films were deposited by magnetron sputtering on Si substrate and quartz maintained at room temperature followed by nanostructuring of the films in RTA as well as on hot substrate between 100 °C – 300 °C during deposition.

The formation of GeSn nanocrystals/dots in the GeSnSi3N4 films was achieved by optimizing the necessary parameters: (i) RTA heat treatment in the range 325 - 700 °C and (ii) in-situ depositions on hot substrate in the range 100 - 300 °C.

The investigated morphology and structure of the films show a strong dependence on the Sn concentration in the films. The films obtained on hot substrate (300 °C) have a low degree of crystallization in films with ~4% Sn but as the Sn content increases to ~18% both the density of GeSn crystals and their size increase but Sn diffusion also appears on the film surface. This is also highlighted by XRD investigations.

Also, optical investigations highlight the influence of Sn concentration in the films on the absorption threshold. In films where the Sn concentration is approximately 18 %vol., the absorption threshold has a value of 0.36 eV compared to the value of 1 eV corresponding to a Sn concentration of ~4 %vol.

The I – V characteristics show: (i) the photocurrent is higher by 5 orders of magnitude compared to the dark current, dependent on the measurement temperature; (ii) the response rate is between 0.9 – 2ms; (iii) junction dependent on Sn content and deposition method. The spectral dependence of the photocurrent shows a wide sensitivity band, in the range 360 - 2200 nm (UV-VIS-SWIR).

The results obtained from the optical investigations are in close agreement with the photoelectric ones and demonstrate that these films have adequate photoconductive properties for making photodetectors. The demonstrator photodetector was manufactured, by processing in a clean room, based on the optimized technological parameters in these initial stages. This was tested to determine the influence of the active surface on the spectral sensitivity.

In conclusion, the objectives and activities proposed for Stage II/2023 have been fully achieved.

Etapa III/2024

In Stage III/2024, the fabrication of the photodetector-demonstrator was carried out using the technological parameters optimized in the two previous stages. The films were deposited by magnetron sputtering on a Si substrate at room temperature and on a hot substrate during deposition. The optimization of the parameters was achieved through step-by-step adjustments based on the results obtained in the opto-electrical measurements, namely: (i) Sn concentration in the range of 4-18 vol%; (ii) RTA thermal treatments in the range of 325 - 700°C, but also (iii) in-situ depositions on a hot substrate in the range of 100 - 300°C.

The I – V and I – t characteristics show that, depending on the parameters used in the fabrication of the demonstrator: (i) the photocurrent can be over 5 orders of magnitude higher than the dark current and is strongly dependent on the measurement temperature; (ii) the response speed is less than 0.8 – 0.9 ms, depending on the acquisition time; (iii) the spectral dependence of the photocurrent exhibits a broad sensitivity band, starting from the visible (365 nm) and reaching up to approximately 2400 nm in the SWIR; (iv) the maximum responsivity obtained is 8.2 AW^-1, obtained at approximately 900 nm; (v) the detectivity is high in a broad spectral range, 450 – 2000 nm.

The results obtained by testing the photodetector-demonstrator demonstrate that these films have suitable photoconducting properties for the fabrication of photodetectors.

In conclusion, all the objectives and activities proposed for Stage III/2024 have been fully achieved.

2022

ISI indexed paper:

“Extended near infrared photo-response influenced by host matrix change in Ge nanoparticle-based films”_, I. Stavarache, C. Palade, A. Slav, P. Prepelita, V. S. Teodorescu, M. L. Ciurea, IEEE conference, 45th Edition of International Semiconductor Conference (CAS), pp. 231-234, 2022 October 12-14, Sinaia, Romania; IEEE Catalog Number: CFP22CAS-USB;
ISBN: 978-1-6654-5253-3; DOI: 10.1109/CAS56377.2022.9934586

2023

ISI indexed paper:

“Near infrared photo-response of as-deposited films based on GeSn nanoparticles in Si3N4 dielectric”_, I. Stavarache, P. Prepelita, O. Cojocaru, V. S. Teodorescu, M. L. Ciurea, IEEE conference, 46th Edition of International Semiconductor Conference (CAS), pp. 259-262, 2023 October 11-13, Sinaia, Romania; IEEE Catalog Number: CFP23CAS-USB;
ISBN: 979-8-3503-2394-8; DOI: 

ISI papers:

"Enhancing Short-Wave Infrared Photosensitivity of SiGe Nanocrystals-Based Films through Embedding Matrix-Induced Passivation, Stress, and Nanocrystallization", A.-M. Lepadatu, I. Stavarache, C. Palade, A. Slav, I. Dascalescu, O. Cojocaru, V.-A. Maraloiu, V. S. Teodorescu, T. Stoica, M. L. Ciurea, Phys. Chem. C 128, 4119−4142 (2024); https://doi.org/10.1021/acs.jpcc.3c06996; Rank by Journal Impact Factor: Q2/2022

"Modulating SiGe-SiO2 VIS-SWIR photoresponse by rapid-like furnace annealing versus rapid thermal annealing by interplay between strain and defects", Muhammad Taha Sultan, Ionel Stavarache, Andrei Manolescu, Unnar Bjarni Arnalds, Valentin Serban Teodorescu, Halldor Gudfinnur Svavarsson, Snorri Ingvarsson, and Magdalena Lidia Ciurea, Journal: Advanced Photonics Research; Manuscript ID: adpr.202300316; Rank by Journal Impact Factor: Q2/2022

2024

ISI papers:

"Enhancement of Visible to Short-Wave Infrared Photoresponse in Germanium Nanoparticles Embedded in Silicon Nitride by Thermal Annealing", Ionel Stavarache, Petronela Prepelita, Sorina Ieftimie, Valentin Serban Teodorescu, Valentin Adrian Maraloiu, Magdalena Lidia Ciurea, Toma Stoica, Journal: The Journal of Physical Chemistry, Part: Part C; Manuscript ID: jp-2024-03158v; Rank by Journal Impact Factor: Q2/2022

Patent applications:

“Fotodetector sensibil in VIS-SWIR pe baza de nanoparticule de germanium-staniu inglobate in nitrura de siliciu si la un procedeu de abtinere a acestuia”/"Visible-shortwave infrared sensitive photodetector based on germanium-tin nanoparticles embedded in silicon nitride and a process for obtaining it"_, Stavarache, T. Stoica, M. L. Ciurea; A/00232 din 30 Aprilie 2024