Ultrafast carrier thermalization dynamics in amorphous semiconductor materials

Summary form only given. Amorphous semiconductors are of interest for both their technological applications and the underlying physics of the unusual properties that result from the departure from crystalline order. Amorphous silicon in particular has become the prototype material for understanding the electronic properties of disordered systems. Previous time-resolved studies of photoexcited carriers in this and related materials have revealed complex carrier dynamics and have shown that, at moderately high carrier densities, the time-resolved response is dominated by bimolecular recombination on picosecond time scales. However, important questions remain about the detailed mechanisms of the carrier dynamics, and especially the initial energy relaxation processes. In this work, we have carried out systematic studies of amorphous silicon and silicon-germanium alloys as a function of excitation density, temperature, and material composition. The high time resolution of the measurements has allowed us to directly address the initial relaxation dynamics.