SURFACE RECOMBINATION AT THE N-GA1-XALXAS-ELECTROLYTE INTERFACE - A STUDY BY INTENSITY-MODULATED PHOTOCURRENT SPECTROSCOPY

The photoelectrochemical behaviour of epitaxial samples of n-Ga1-xAlxAs (0 less-than-or-equal-to x less-than-or-equal-to 0.31) has been investigated by several methods, including intensity-modulated photocurrent spectroscopy, under conditions where photoetching takes place. The surface potential distribution was found to be non-ideal; it depends on the level of illumination and on the pretreatment of the electrode. The potential dependence of the surface recombination rate has been used to derive the band bending in the semiconductor as a function of electrode potential. Extensive Fermi level pinning is observed close to flat band, and this has been related to the formation of adlayers by reduction of soluble arsenic(III) and gallium(III) species. High rates of surface recombination were observed after the electrochemical passivation of GaAlAs by a 5 nm oxide layer, indicating that the presence of an anodic oxide layer greatly increases the surface state density and reduces the band bending.