Composition of GaAs anodic oxide films studied by low energy ion scattering spectrometry (ISS)

Thin oxide films (525 A to 2100 A thick) were formed on N type GaAs substrates, 100 oriented, by anodic oxidation at constant current up to a predetermined voltage, followed by a stage at constant voltage. The oxidation bath was diethylene glycol + 3.10-2M. Na3PO4. The oxide composition was analyzed by ISS using a low energy ion beam (1.5 keV 4He+ and 2.5 keV 20Ne+). Parasitic effects associated with erosion (knock-on effects and preferential erosion) appeared negligible, since depth resolution about +- 70 A after 2100 A has been obtained. Oxidations at low current density (25 μA cm-2) yields to oxides having uniform composition in depth, and abrupt oxide/GaAs interface. The composition of anodic layers formed at 1 mA cm-2 seems to depend strongly on experimental conditions (current density, current decay or final oxidation voltage); in this case bulk composition is uniform while surface and interfacial regions exhibit graded arsenic and gallium profile. (Auth.)