GeSiSn photodiodes with 1 eV optical gaps grown on Si(100) and Ge(100) platforms

Ge _1-x-ySi _xSn _y alloys have reached a level of maturity that permits the creation of prototype devices on group-IV platforms. Here, we compare the optical and electrical properties of GeSiSn diodes with similar target compositions (Si; 10-11%, Sn; 1.7-2.3%) grown directly on Si(100) and Ge(100) using low erature ultrahigh vacuum chemical vapor deposition reactions of designer hydrides. The diodes grown on Ge substrates have relatively low ideality factors in the 1.3-1.4 range and low dark currents with a sizable diffusion component. The corresponding characteristics of the analogous devices grown on Si are significantly degraded due to mismatch-induced reduction in crystal quality. Quantum efficiency measurements show that both sets of diodes have absorption edges near 1eV with collection efficiencies reaching at least 76% in the devices grown on Ge. Collectively, these results suggest that Ge _1-x-y Si _xSn _y alloys represent a viable alternative as the long sought photovoltaic material with a lattice constant equal to that of Ge and a bandgap around 1eV.