Electron spin resonance studies of tetrahedral amorphous semiconductors

Electron spin resonance (ESR) and optically induced electron spin resonance (LESR) measurements on hydrogenated amorphous silicon (a-Si:H) and germanium (a-Ge:H) are useful probes of both charge carriers in localized electronic states near the edges of the conduction and valence bands (band-tail states) and defects, such as silicon and germanium dangling bonds.; Theoretically, the transport and recombination processes of band-tail carriers are easiest to understand at very low temperatures where the diffusion and recombination of electrons and holes is a universal property that does not depend on the functional form for the density of localized electronic states.{09}This universal property disappears at finite temperatures where variable range hopping of the charge carriers, which does depend on the density of localized electronic states, becomes important. Transient LESR experiments are reported for a-Si:H over approximate times from 10 ms to 3000 s at temperatures up to approximately 100 K. These results are compared to the expectation of theoretical models.; The most common metastable effect in a-Si:H and a-Ge:H is an increase in the density of silicon or germanium dangling bonds, which are the primary defects measured by ESR. For this reason it is important to understand the kinetics for the production and annealing of these dangling bonds. ESR measurements are reported for the first time on hydrogenated amorphous germanium (a-Ge:H). The ESR measurements performed on a-Ge:H verify that the inducing and annealing kinetics for the metastabilities in a-Si:H and a-Ge:H are similar. These results place restrictions on acceptable microscopic models to explain the kinetics.; In addition, tritiated samples of a-Si were investigated where the metastable defect was induced by the decay of the tritium in the sample instead of by absorption of light. In the case of tritium, each tritium decay produces a defect, while in optically induced experiments the efficiency for the production of defects is unknown but thought to be low. The comparison of these two production processes provides a better understanding of how metastable defects are produced and annealed in a-Si:H.