ON THE FACTORS DETERMINING THE MORPHOLOGY OF WET-ETCHED N-GAP AND P-GAP SINGLE-CRYSTAL SURFACES

Wet etching of [111]-oriented GaP single crystals is performed in aqueous KOH solutions at different anodic potentials for p-type and at different anodic potentials and illumination levels for n-type samples. Furthermore, both n- and p-type crystals are photoetched in KOBr solutions at open-cricuit potential. The influence of the rate-determining step on the etching morphology is shown. The difference in etching selectivity between the (111) and (111BAR) face is explained by the different orientation of the Ga-P dipole, resulting in a different reactivity for hole capture. The KOBr photoetch results in the formation of etch hillocks at n-type crystals, whereas etch pits are developed at p-type crystals. This result is explained by the fact that only local variations in the anodic partial current of the process are reflected in the etching morphology.