OJDOS EVIDENCE FOR A SEMICONDUCTOR-TO-METAL TRANSITION IN A-SI1-YNIY H

Reflectivity measurements over the energy range 0.5-12 eV have been made for the amorphous alloy system a-Si(1-y)Ni(y) = 0.0,0.11,0.28,0.45. The infrared region of the reflectivity shows evidence of a semiconductor-to-metal transition as y is increased, whilst the visible/ultraviolet regions show a systematic shift in energy of prominent features. Using suitable extrapolations to the reflectivity data, Kramers-Kronig analysis has enabled the determination of epsilon-1, epsilon-2 and hence the OJDOS (optical joint density of states) for the system. A schematic valence and conduction band DOS has bee deduced from these data in conjunction with the previously determined variation of optical bandgap with composition.