X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY OF NATIVE OXIDES ON GAAS

The identification and distribution of chemical species comprising the native oxides of anodically and thermally grown films have been studied using XPS in conjunction with ion milling and chemical etching. Low angle electron diffraction was used to identity crystalline surface (~150Å) layers of GaAsO4 produced thermally from AS2O3/O2 mixtures at elevated (T > 600°C) temperatures. At lower growth temperatures (T ~ 500°C) an amorphous modification of this product is indicated. The primary bulk constituents of all films, both anodically and chemically grown, were found to be AS2O3 and Ga2O3. In anodic films the molar ratio of As2O3/Ga2O3 was approxim ately unity and uniform from the surface to the oxide/GaAs interface. The anodic interface width was found to be relatively sharp (100-120A). Water rinsing of anodic films dissolves the AS2O3 from the near surface (~200Å) volume. Annealing of 2000Å anodic films at 650°C/N2 for periods from 1 to 16 hr generated a pentavalent arsenic component which was limited to the surface. A general feature of the thermal oxides was the loss of AS2O3 from the bulk film. In air-grown samples (530°C, 4 hr) this loss was nearly complete and the native oxide was primarily Ga2O3 with some addition of nonuniformly distributed elemental arsenic and unoxidized GaAs. The use of AS2O3/O2 mixtures failed to produce bulk oxides with a high, uniform concentration of AS2O3. Studies comparing ion milling and chemical etching demonstrated the existence of artifacts associated with argon beam reduction of AS2O3 in anodic films even though virtually no reduction of crystalline or vitreous AS2O3 control samples was observed. © 1979, The Electrochemical Society, Inc. All rights reserved.