Fibered and Epitaxial Growth in Sputtered Films of GaAs

Abstract

The crystal texture of GaAs films sputtered onto vitreous silica and polished CaF2 substrates has been investigated by electron diffraction and microscopy, and by x-ray diffraction, over a substrate temperature range from room temperature up to 600°C. On silica substrates the GaAs films possess either an amorphous structure or a crystalline structure with one-degree orientation of the crystallites, depending on the substrate temperature and on the sputtering condition at the growing surface. In cases where the anode substrate support is kept in the positive column of the discharge a predominant 〈111〉 orientation is present over the whole temperature range. When the GaAs films are deposited on a substrate in the Faraday dark space, however, they are amorphous up to about 400°C, and show a 〈110〉 texture up to 510°C that changes abruptly to a 〈111〉 texture with further temperature increase. The persistence of the 〈111〉 texture, under anodic glow conditions at low nominal substrate temperatures is attributed to indirect heating derived from energy liberated at the growing surface. The use of a polished crystal of CaF2 in place of the vitreous silica substrate does not alter the observed orientation effects. Electron diffraction studies have also been made of the growth of GaAs films on single-crystal Ge substrates. In GaAs films sputtered onto the (100), (110), and (111) faces of Ge, epitaxial growth occurs at elevated temperatures but is only complete above 560°C, and is usually associated with extensive twinning. At temperatures above 580°C breakdown of the epitaxial structure occurs and appears to be associated with loss of arsenic.