Wet etching of GaAs using synchrotron radiation x rays

The results of room-temperature wet etching of GaAs using synchrotron-radiation x rays are described. Under x-ray illumination, etching occurs on the n-GaAs surface in contact with an acid or base solution or even deionized water. The etching process is studied as functions of the electrolytes, their concentration, semiconductor doping level, and x-ray intensity and energy. The etching mechanism is determined to be primarily electrochemical in nature, but the x-ray radiation chemistry plays a role in the etching. Smoothly etched surfaces are achievable with a root-mean-square surface roughness of 0.7–2.0 nm. We also found that the etching rate increases substantially with the ratio of the sample size to the x-ray exposure size. This is accounted for by the rate-limiting effect on the charge transfer across the semiconductor-electrolyte junction. The chemistry of etched surfaces is studied using x-ray photoelectron spectroscopy and compared to that of as-received surfaces.