OPTICAL-BOND GAP AND TAUC GAP IN A-SIOX-H AND A-SINX-H FILMS

Changes in the joint density of state (JDOS) of a-SiOx:H and a-SiNx:H films with x were investigated by optical measurements. The optical bo nd gap E(o) which corresponds to the bonding-antibonding splitting ene rgy was deduced from the dispersion of the refractive indices based on a single-oscillator model. The energy of the Si-Si bond, E(o)(Si-Si), was estimated from E(o). The Tauc gap energy E(t) and the energy widt h of the linear tail were determined from optical transmission spectra . The correlation among these characteristic energies was investigated to estimate the JDOS in these alloys. It was found that E(o)(Si-Si) i ncreases with x, while the bandwidth of JDOS derived from the Si-Si bo nd is kept constant for both a-SiOx:H and a-SiNx:H systems. This sugge sts that the increase in the Tauc gap energy is due to the increase in Si-Si bond energy rather than the change in the energy width of the S i-Si-bond-derived JDOS.