Charged defect states in intrinsic hydrogenated amorphous silicon films

Abstract

Steady-state photoconductivity, sub-band-gap absorption and electron spin resonance (ESR) measurements were carried out on annealed and light soaked intrinsic hydrogenated amorphous silicon (a-Si:H) films. The experimental results were modeled using detailed numerical analysis. The defect densities derived from the sub-band-gap absorption in the light soaked films were correlated with the ESR spin densities. Self-consistent fitting of the data was obtained using a gap state distribution which consists of positively charged defect states above, negatively charged defect states below and neutral defect states at about the midgap. Both the annealed and the light degraded states are modeled using the same gap states which increase upon light soaking and have a slight increase in the ratio of the neutral to charged defect densities. These results on intrinsic a-Si:H are consistent with proposed charged defect models and clearly indicate the importance of charged defect states in determining sub-band-gap absorption as well as its correlation with neutral dangling bonds.