The study of fundamental defects in amorphous semiconductors is to be undertaken in four general areas of activity. The proposed work will investigate the nature of the D defect in its different relaxed and unrelaxed states using spin transient measurements and in intrinsic a-Si:H using capacitive transient methods. Doping multilayers will be investigated to study contamination effects and electron trapping into thin regions of the lower gap material. The nature of the c-Si/a-Si:H interface will be examined to understand the effects of the substrate on the a-Si:H electronic structure in the near interface region. The distribution of interface defects will be correlated with ESR and opitcal generation studies. The defect density will be determined in semiconducting transition metal chalcogenides to help develop samples with optimized electronic properties.