Ultrasmooth GaN etched surfaces using photoelectrochemical wet etching andan ultrasonic treatment

We have studied the effect of ultrasonic agitation on the surface of n-type gallium nitride (GaN) layers grown on sapphire that were subjected to a se lective photoelectrochemical etch. Solutions of various concentrations of K OH were used along with an ultraviolet lamp to oxidize the exposed GaN surf ace, resulting in an anisotropic etch. Smooth surfaces with root-mean-squar e (rms) roughness of similar to 4 nm were obtained for a narrow range of et ching conditions. It was found that this window could be extended by using etch conditions which produced "whisker" growth. Subsequent ultrasonic agit ation was then used to remove these whiskers and obtain smoother surfaces w ith the best rms roughness values being similar to 0.9 nm. (C) 1999 The Ele ctrochemical Society. S1099-0062(99)09-032-X. All rights reserved.