Near-surface defects in amorphous semiconductors related to hydrogen incorporation

Abstract

Using total yield photoelectron spectroscopy we demonstrate that the room temperature (RT) hydrogenation of amorphous germanium (a-Ge) surfaces leads to the creation of a deep defect band 0.45 eV above Ev that anneals out at ≈ 300°C. We argue that this defect is related to the high concentration of hydrogen at the growth surface and is responsible for the high surface defect density (≈ 1018 cm−3) in g.d. a-Ge:H and a-Si:H as derived from yield and PDS measurements. We show that the surface defect density in g.d. a-Si:H can be reduced through hydrogen dilution and through post-deposition anneals but not through post-hydrogenation. Drawing from the analogy with c-Si we propose that a small fraction (≈ 10−4) of hydrogen in the bond center position is responsible for the observed defect which is different from the more common dangling bond defect.