SOME OPTICAL-PROPERTIES OF SE-GE-AS AMORPHOUS-CHALCOGENIDE GLASSES

The effects of composition, film thickness, substrate temperature, and annealing of amorphous thin films of Se75Ge25-xAsx (5 less-than-or-equal-to x less-than-or-equal-to 20) on their optical properties have been investigated. X-ray diffraction revealed the formation of amorphous films. The absorbance and transmission of vacuum-evaporated thin films were used to determine the band gap and refractive index. Optical absorption measurements showed that the fundamental absorption edge is a function of glass composition and the optical absorption is due to indirect transition. The energy gap increases linearly with increasing arsenic content. The optical band gap, E(opt), was found to be almost thickness independent. The shapes of the absorption edge of annealed samples displayed roughly the same characteristic as those of the unannealed films, but were shifted towards shorter wavelengths; as a result, E(opt) increased and E(e), the width of the band tails, decreases. The increase in E(opt) is believed to be associated with void removal and microstructural re-arrangement during annealing. The influence of substrate temperature on the optical parameters is discussed.