Anodization and backscattering measurements of superimposed metal film-GaAs structures

Abstract

This paper reports the growth of composite anodic Nb or V oxide and GaAs oxide films on GaAs and studies of the resulting films using Rutherford scattering. The deposited metal films had thicknesses ranging from 6 to 100 nm. These films and a portion of the underlying GaAs where anodized galvanostatically in an acid-glycol-water electrolyte. The resulting voltage time graphs of the composite anodic metal/GaAs system are compared with those measured on the virgin GaAs crystal. Measurements of oxide thickness versus oxide voltage show that the anodization constant is 1.85 nm/V. Rutherford backscattering measurements using 1.6 MeV He + ions are used to measure the composition and the fraction of the composite oxide formed by oxygen ion transport. The latter quantity is measured by implanting a 136Xe layer into the GaAs substrate. The position of the 136Xe layer and its distribution is measured using Rutherford scattering prior and subsequent to anodic oxidation. The results of these measurements are that 82±2% of oxide thickening is due to oxygen transport and the remaining 18% is due to Ga and As transport. This is comparable with measurements of oxygen transport in pure V and Nb systems where it is found to be 72% and 76% respectively. Oxide composition measurements show that both Ga and As are present at the surface of the composite vanadium oxide whereas the niobium oxide is superimposed on the native GaAs oxide in a layered structure.