Thermally and optically induced metastabilities in doped hydrogenated amorphous silicon: ESR studies

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Abstract
Equilibrium and light-induced electron-spin resonance (ESR and LESR) are used to investigate the effects of rapid thermal quenching and light soaking on the electronic density of states in doped hydrogenated amorphous silicon. Thermal quenching is found to lead to a strong, metastable increase in the density of shallow states. Light soaking of phosphorus-doped a-Si:H causes a reversible increase of occupied neutral-donor levels together with a decrease of electrons in conduction-band-tail states. In contrast, n-type material doped with arsenic does not show any light-soaking effect. Possible microscopic mechanisms for the observed metastable changes are discussed, and the difference between phosphorus- and arsenic-doped a-Si:H is explained by changes in the electron trapping behavior deduced from LESR experiments.