THE EFFECT OF VARYING SUBSTRATE-TEMPERATURE ON THE STRUCTURAL AND OPTICAL-PROPERTIES OF SPUTTERED GAAS FILMS

Stoichiometric GaAs films have been prepared by RF sputtering over an appreciable range of substrate temperature T(s). The structural and optical properties of these films have been investigated by means of a variety of experimental techniques. Transmission electron microscope (TEM) experiments reveal that for T(s) greater-than-or-equal-to approximately 70-degrees-C the structure consists of nanocrystals embedded in an amorphous network. EXAFS, XPS and infrared experiments are consistent with each other, indicating that configurational disorder in the amorphous network of the GaAs films decreases as T(s) is raised. Most of the disorder relates to bond-angle disorder; the spread in bond angle around Ga atoms is found to be less than that around As atoms for a given substrate temperature. The changes observed in the fundamental absorption edge with increasing T(s) are discussed in relation to various possible defects in amorphous GaAs.