Identification of the dominant electron deep trap in amorphous silicon from ESR and modulated photocurrent measurements: implications for defect models

Abstract

Modulated photocurrent (MPC) measurements in intrinsic a-Si:H reveal a prominent band of electron traps with a thermal emission energy near 0.6 eV. We have identified this defect band by comparing MPC and electron paramagnetic resonance spectra for intrinsic and lightly n-type doped samples over a range of metastable states. These data directly show that the MPC band arises from the neutral charge state of the defects. This identification is also confirmed when the quasi-Fermi level is varied by the application of light bias. Such observations are totally inconsistent with a large population of charged defects in intrinsic samples predicted by recent versions of the defect pool model. Rather, our observations have a natural explanation in terms of a defect relaxation process.