Rapid Reversible Light-Induced Crystallization of Amorphous Semiconductors

Abstract

We have observed a high-speed crystallization of amorphous semiconductor films and the reversal of this crystallization back to the amorphous state using short pulses of laser light and evidenced by a sharp change in optical transmission and reflection. This optical switching behavior is analogous to the memory-type electrical switching effect in these materials which has received wide attention¹ since the observation by S. R. Ovshinsky² of both threshold and memory switching in amorphous semiconductors. In this letter, we propose a model which closely relates the optical and electrical switching behavior, and shows that the phase change from amorphous to crystalline state is not only a thermal phenomenon but is directly influenced by the creation of excess electron-hole carriers by either the light, or, for the electrical device, by the electric field. The reversibility of the phenomenon in this model is obtained through the large difference in crystallization rates with the light on or off.