Highly selective photoelectrochemical etching of nitride materials for defect investigation and device fabrication

Photoenhanced electrochemical (PEC) etching in an unstirred KOH solution un der He-Cd laser illumination was used for delineating extended defects in G aN films. When a low-excitation intensity was employed, the process yielded threading vertical features at dislocation sites. Application of an extern al voltage or a higher-illumination intensity led to high-etch rates with s mooth surfaces. Some highly resistive samples, for which no etching was obt ained under normal etching conditions, could be etched with the application of a single-polarity external voltage. Finally, in a GaN sample with an Al N/GaN superstructure inside, high selectivity between AIN and GaN was achie ved; in this case, the PEC process stopped at the thin AIN stop layer. (C) 2001 American Vacuum Society.