The combined use of He back-scattering and He-induced X-rays in the study of anodically grown oxide films on GaAs

Anodic oxide films on GaAs have been studied by the combined use of He back-scattering and He-induced X-rays. Back-scattering is hampered by the lack of mass resolution between Ga and As. X-ray analysis has excellent mass resolution but poor depth resolution. This poor depth resolution is overcome by increasing the effective thickness of the films by entering at grazing angles and making use of the property that the He-induced X-ray cross sections fall steeply with decreasing energy. This technique and the methods of data analysis are discussed in detail. The anodic oxide films are found to be deficient in As within 200 Å of the surface and to have a Ga:As ratio of approximately 1:1 for the rest of the oxide. On heating to 650°C most of the As diffuses out of the films.