Selective area formation of arsenic oxide-rich octahedral microcrystals during photochemical etching of n-type GaAs

We demonstrate how to spatially localize the formation of octahedral arsenic oxide microcrystals in selective areas of highly doped n-type GaAs substrates during rapid digital projection photochemical (PC) etching with sulfuric acid. We captured a time lapse video that shows that these crystal-like octahedral structures grow to various sizes ranging from 5 μm to 100 μm. By conducting a series of different studies, we identified the etch rate, the area of illumination, the acid type, and the substrate quality as major factors that affect crystal formation. In particular, we observed that the structures only formed in the high etch rate illuminated regions of the wafer. Moreover, they only formed when the area of illumination was adequately large. The structures formed but then partially dissolved when hydrochloric acid was used. Lastly, we observed the growth of individual microcrystals for prime grade wafers but the formation of a network of microcrystalline features for mechanical grade wafers.