Relation between electron-spin-resonance and constant-photocurrent-method defect densities in hydrogenated amorphous silicon

The cause of a large discrepancy between the defect densities evaluated by electron spin resonance (ESR) and the constant photocurrent method (CPM) in a-Si:H was investigated. a-Si:H films of various thicknesses were light-soaked with both white light and red light to increase the defect density. The defect densities for these light-soaked films were evaluated both by ESR and CPM. The results were reproduced fairly well by a computer simulation by taking into account the inhomogeneous defect distribution across the film thickness caused by a penetration depth of the light smaller than the film thickness. The presence of negatively charged dangling-bonds was found to also contribute to the discrepancy between the defect densities evaluated by ESR and CPM for the thin film light-soaked with the red light in addition to the inhomogeneous distribution of defects.