Nature and growth of anodic and thermal oxides on GaAs and AlxGa1-xAs

This paper considers the nature of anodic and thermal oxides on GaAs and AlxGa1-xAs, with x = 0.2, 0.5 and 0.8. Anodic oxides were produced in NH4H2PO4 solution and thermal oxides formed in O-2 at 500 degrees C. The chemical composition of the oxides (less than or equal to 30 nm thick) has been evaluated using secondary ion mass spectrometry (SIMS), complemented by X-ray photoelectron spectroscopy (XPS) and other techniques. Anodic oxides on GaAs comprise both Ga2O3 and As oxides. For AlxGa1-xAs, Ga is enriched in the outer part of the film due to Ga-phosphate formation. The higher the Al content in the oxide, the less Ga-phosphate is present. Al is enriched at the inner interface, the amount increasing with increasing Al content in the substrate. These anodic films basically comprise a three-layer structure: Ga phosphate:Ga/As oxide:Ga/As/Al oxide. Thermal oxides on GaAs consist almost entirely of Ga2O3, with a small As enrichment at both the gas-oxide and the oxide-substrate interfaces. This is also the case for thermal films on Al0.8Ga0.2As, but now the main components of the film are Ga2O3 and Al2O3. Unlike anodic oxides, thermal oxides on both AlxGa1-xAs and GaAs are stable in the air and do not change perceptibly over a period of several months. (C) 1999 Elsevier Science Ltd. All rights reserved.