Nature and growth of anodic and thermal oxides on GaAs and Al xGa 1−x As

Abstract

This paper considers the nature of anodic and thermal oxides on GaAs and Al x Ga 1− x As, with x=0.2, 0.5 and 0.8. Anodic oxides were produced in NH 4H 2PO 4 solution and thermal oxides formed in O 2 at 500°C. The chemical composition of the oxides (⩽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 Ga 2O 3 and As oxides. For Al x Ga 1− x As, 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 Ga 2O 3, with a small As enrichment at both the gas–oxide and the oxide–substrate interfaces. This is also the case for thermal films on Al 0.8Ga 0.2As, but now the main components of the film are Ga 2O 3 and Al 2O 3. Unlike anodic oxides, thermal oxides on both Al x Ga 1− x As and GaAs are stable in the air and do not change perceptibly over a period of several months.