INFLUENCE OF AS EXCESS ON THE OPTICAL-PROPERTIES OF AMORPHOUS GAAS

Amorphous GaAs thin films (a-GaAs) were prepared by RF sputtering. The As to Ga atomic concentration (C(As)/C(Ga)) was controlled by varying the substrate temperature T(s). The C(As)/C(Ga) ratio is found to decrease from 1.22 to 1.05 as T(s) increases from 40 to 250-degrees-C. Absorbance measurements shows no significant change in either the optical gap or the band tail width as C(As)/C(Ga) varies between 1.22 and 1.05. A small blue shift of the absorption edge is observed. It is concluded that most of the defects associated with excess As lie energetically outside the studied energy range.