(PHOTO-)ELECTROCHEMICAL INVESTIGATION OF THE PHOTOETCHING OF N-TYPE AND P-TYPE (100) INP IN AQUEOUS FE-3+-CONTAINING SOLUTIONS

The etch rate of the n- and p-type InP single crystal (100) face was measured in aqueous acid Fe3+ solutions, in darkness as well as under illumination, using a flow-cell set-up. The influence of the flow rate, the light intensity, the Fe3+ concentration and the further electrolyte composition was studied. By an electrochemical investigation, including cyclic-voltammetric and RRDE techniques, it was shown that under illumination in HCl medium at pH = 0, a photoetching process predominates, involving two compensating partial currents, which correspond to the six-equivalent anodic dissolution of InP and to the cathodic reduction of Fe3+ via the conduction band, respectively. Illumination was necessary for inducing one of the two partial currents, depending on the semiconductor type. The observed influence of the electrolyte composition upon the etch rate is shown to be associated with shifts of both the partial currents.