THE MECHANISM OF THE PHOTOELECTROCHEMICAL ETCHING OF P-INP IN NITRIC-ACID SOLUTIONS

The mechanism of the photoelectrochemical (PEG) etching of p-InP in ni tric acid was investigated. The success of the procedure is shown to b e due to the chemical oxidation of the photoproduced metallic indium b y nitric acid. The study gives insight into how the photoreduction of p-InP and protons occur simultaneously Plots of the etch rate vs. nitr ic acid concentration for two p-InP electrodes with different carrier concentrations and etch pit densities (EPD) indicated that defects pla y a role in the photoreduction process. The effect of EPD on the photo reductions;has been interpreted in terms of surface states which origi nate from EPD; the EPD are correlated with the magnitude of the surfac e states. The total number of coulombs passed in the PEC etching regio n was found to be relatively constant for each p-InP electrode. Compar ison of the charge transferred with the PEC etch rates indicated that the majority of protons are photoreduced via surface states. A positiv e shift of the onset potential for photocurrent with increasing nitric acid concentrations implied a decrease in the density of surface stat es. This observation was correlated with the participation of the cond uction band in the photoreduction of p-InP. At higher nitric acid conc entrations, experiments indicate that the photoreduction of protons is possible at both the surface states and conduction band. Energy diagr ams lend support to these suppositions.