Ultraviolet photoenhanced wet etching of GaN in K2S2O8 solution

The mechanism of the UV photoenhanced wet etching of GaN is determined. The UV photoenhanced wet etching does not require an electrical contact to be made to the sample, and nitrides deposited on insulating substrates (such a s sapphire) can be etched, unlike photoelectrochemical (PEC) wet etching. T he present technique relies on adding an appropriate oxidizing agent, in th is case, peroxydisulfate (S2O82-), to KOH solutions. In a similar mechanism to PEC wet etching, the regions of low defect density are preferentially e tched, leaving regions of high electron recombination such as threading dis locations relatively intact. The threading dislocations may be physically b roken off, either by stirring or by a postetch sonication of the sample in KOH solution. Smoothly etched surfaces can be obtained under the proper con ditions. A noble metal mask acts in a catalytic manner, yielding etch rates approximately one order of magnitude greater than those observed using ine rt masks. The essential role of the free radicals, originating from the per oxydisulfate ion, in the etching reaction is confirmed. The etching reactio n is more rapid for more heavily n-type doped samples, and insulating C-dop ed layers act as an etch stop layer. (C) 2001 American Institute of Physics .