Compositional dependence of the absorption edge and dark currents in Ge_1−x−ySi_xSn_y/Ge(100) photodetectors grown via ultra-low-temperature epitaxy of Ge₄H₁₀, Si₄H₁₀, and SnD₄

Lattice-matched Ge_1−x−ySi_xSn_y (x ≤ 0.2, y ≤ 0.05) alloys were deposited defect-free on Ge(001) substrates via low-temperature (330–290 °C) reactions of Ge₄H₁₀, Si₄H₁₀ and SnD₄ hydrides, and used to fabricate pin photodetectors. The growth is carried out under gas-source molecular beam epitaxy conditions in a specially designed single-wafer reactor. Optical responsivity measurements reveal absorption edges between 0.88 eV and 0.98 eV, which are used to determine the compositional dependence of the direct band gap. A study of the I-V characteristics of the diodes shows that the dark current is very weakly correlated with the number of Si-Sn bonds in the alloy.