Gap-State Distributions in Hydrogenated Amorphous Silicon-Germanium Evaluated Using Capacitance–Voltage Method

Abstract

The density of gap states in hydrogenated amorphous silicon-germanium (a-SiGe:H) alloys deposited at temperatures of 150–250°C has been evaluated by using a capacitance–voltage (C–V ) method. It was found that the gap-state distribution for a-SiGe:H deposited at 150°C has a broad bump around 0.6 eV below the conduction band edge Ec which is associated with Ge dangling bonds. In contrast, a 250°C-deposited film exhibits a peak density of 8×1018 cm-3·eV-1 around 0.75 eV below the conduction band edge Ec, which might originate from Ge and/or Si dangling bond states. After AM1 (200 mW/cm2) light soaking, the gap-state density above the midgap is increased for films deposited below 200°C, while at 250°C deposition, defect states near the midgap are increased.