Wide optical-gap a-SiO:H films prepared by rf glow discharge

Hydrogenated amorphous silicon oxygen alloy (a-SiO:H) films have been prepared at a temperature of 200 degrees C by arf plasma deposition process. A controlled widening in the optical gap (E(g)). has been obtained by diluting SiH4 with CO2 in the rf plasma. The refractive index (n) decreases, dark conductivity (sigma(d)) as well as photoconductivity (sigma(ph)) decreases, the Si-dangling bond density (N-s) increases, and the widening of the optical gap is caused by O-incorporation in the a-Si:H network. However, up to an optimum level of O-incorporation sigma(ph) decreases by a factor of 5 only, photosensitivity (sigma(ph)/sigma(d)) increases and N-s remains virtually unchanged. Further O-incorporation results in a degradation of optoelectronic properties. A correlation between optical and electrical properties suggests that it occurs when the Fermi level passes through the mid gap (Delta E = E(g)/2) and sigma(o), the prefactor for sigma(d), attains a magnitude similar to that for a-Si:H. N-s has been observed to be less than that reported earlier for a similar optical gap.