Correlation between the valence- and conduction-band-tail energies in hydrogenated amorphous silicon

We provide experimental evidence for a correlation between the characteristic energies of the exponential conduction- and valence-band tails of hydrogenated amorphous silicon (a-Si:H). We measured subgap optical-absorption spectra of isolated a-Si:H films in order to extract their valence-band-tail energies. Also, we modeled the current-voltage characteristics of thin-film transistors which had a-Si:H layers deposited identically to the isolated films, in order to extract their conduction-band-tail energies. When the quality of the a-Si:H was varied, the characteristic energies of the two tails sealed linearly with each other. (C) 1996 American Institute of Physics.