Stage I and II /2021

Photoconductive Ge_xSn_1-x:H nanostructures with various Sn concentrations in GeSn nanocrystals were obtained by the magnetron sputtering method . The hydrogenation of the structures was done by RTA in the temperature range 150 ^oC­­­ –  400 ^oC in the atmosphere of H₂ and by deposition in working gas (Ar) with 10% and 30% H. In the case of in-situ hydrogenation the substrate temperature was maintained at 30 ^oC (RT) and 200 ^oC. For Ge_xSn_1-x co-deposited and hydrogenated by RTA, through increasing the annealing temperature and the Sn concentration we obtained the increasing of the Ge:Sn ratio in the GeSn nanocrystals, simultaneously with the increase the content of segregated Sn in the β-Sn phase. GeSn nanocrystals are formed at low annealing temperatures (150 ^oC and 300 ^oC) without arising the β-Sn phase (up to 400 ^oC). By increasing the annealing temperature, the Sn concentration in nanocrystals decrease down to ~ 7%. Shifting diffraction peaks to small  2q angle shows that the lattice constant increase by including Sn in the Ge crystalline lattice. Electron microscopy images shows columnar crystalline areas alternating with amorphous zones with lengths of 25 ­­­– 35 nm and 7 nm size. By EDX compositional analysis the Sn concentrations  was evaluated between 7.55% and 9.94%, values ​​that are in good agreement with the results obtained by µ-Raman spectroscopy. Also, from XPS we found similar  values for Sn concentration in the GeSn nanocrystals. From the Tauc representation of the optical absorption coefficient we evaluate the effect of hydrogenation on defect states. Also, by FT-IR spectroscopy the Ge-H vibration mode was evidenced at 1873 cm ^-1. The I-V electrical measurements showed a strong rectifying character of the Ge_xSn_1-x:H structures at low temperatures due to the GeSn heterojunction with the Si support. For the Ge_xSn_1-x:H samples with 30% H, the spectral response was extended up to 2 µm in comparison to samples with weaker hydrogenation (10%). In addition, better hydrogenation decreases the dependence of the photocurrent on the bias voltage by reducing the defect states in the gap.

• "Nanocrystallized Ge-rich SiGe-HfO₂ Highly Photosensitive in Short-Wave Infrared", C. Palade, A.M. Lepadatu, A. Slav, V.S. Teodorescu,T. Stoica, M.L. Ciurea, D. Ursutiu, C. Samoila , Materials 2021, 14, 7040;
  https://doi.org/10.3390/ma14227040