EFFECT OF BAND-STRUCTURE ON ETCH-STOP LAYERS IN THE PHOTOELECTROCHEMICAL ETCHING OF GAAS/ALGAAS SEMICONDUCTOR STRUCTURES

We have examined the limitations on selectivity of thin dopant-selective and band-gap-selective etch-stop layers in the photoelectrochemical (PEC) etch process. The ultimate selectivity of one layer from an underlying layer is affected not only by differences in material composition, but also by the sequencing of the layers within the structure which will determine the distribution of the photogenerated carriers. Three semiconductor structures with variations in both doping and band gap were etched to demonstrate this effect. A He-Ne laser (633 nm) and a tunable Ti/sapphire laser (690-830 nm) were used as light sources and a (1:20) HCl:H2O solution was the electrolyte.