Influence of As excess on the optical properties of amorphous GaAs

Abstract

Amorphous GaAs thin films (a-GaAs) were prepared by RF sputtering. The As to Ga atomic concentration (CAs/CGa) was controlled by varying the substrate temperature Ts. The CAs/CGa ratio is found to decrease from 1.22 to 1.05 as Ts increases from 40 to 250 degrees C. Absorbance measurements shows no significant change in either the optical gap or the band tail width as CAs/CGa varies between 1.22 an 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.