Local oxide growth on the n-GaAs surface studied by small area XPS

The photoanodic dissolution of n-GaAs was investigated in a buffered solution at an intermediate pH (pH 9). At this pH, the GaAs dissolution rate was limited by the growth of an anodic oxide film. A laser illumination leads to a local oxide growth only in the illuminated part on to GaAs. Transient photocurrent and capacitance measurements clearly show dissolution kinetics in two steps: the first step is about a few tens of seconds and is correlated with gallium oxide dissolution, and the second step is greater than a few minutes, indicating the origin of at least two surface films onto GaAs. A parallel approach using in-situ electrochemistry and ex-situ surface analysis (XPS) was performed to characterise the growth of an anodic film on to GaAs. A gallium enrichment was detected on this oxide film. The arsenic deficiency in this oxide results from a higher arsenic oxide solubility. The limitation of the GaAs dissolution is due to the dissolution of gallium oxide at pH 9.