Optical monitoring of photodissolution kinetics in amorphous As-S films

Abstract

The kinetics of the photodissolution of silver into amorphous As-S films of various compositions in the range As₄₀S₆₀ to As₂₀S_B0 has been investigated by monitoring the changes that occur in their reflectivity during the photodissolution process. It was found that as the S content was increased above 60at.% the rate of photodissolution increased to a maximum at around As₃₃S₆₇ and then decreased, the maximum rate being approximately double that for As₂₀S₈₀. This is attributed to the fact that only compositions within a few at.% of As₃₃S₆₇ yield a homogeneous material when photodoped; compositions outside this range yield a photodoped product with a phase-separated structure which may impede the passage of electrons through the photodoped layer. The effect of using silver-copper alloys as the metal source instead of pure silver has also been investigated and was found to increase the photodissolution rate by up to 12%. The photodissolution rate and the form of the time dependence of the process were also found to be dependent on the thickness of the silver layer used as the ion source. Thin silver films yield a slower rate and a diffusion-limited process whereas thick films yield a faster rate and a reaction-limited process.