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 as sapphire) can be etched, unlike photoelectrochemical (PEC) wet etching. The present technique relies on adding an appropriate oxidizing agent, in this case, peroxydisulfate (S2O82−), to KOH solutions. In a similar mechanism to PEC wet etching, the regions of low defect density are preferentially etched, leaving regions of high electron recombination such as threading dislocations relatively intact. The threading dislocations may be physically broken off, either by stirring or by a postetch sonication of the sample in KOH solution. Smoothly etched surfaces can be obtained under the proper conditions. A noble metal mask acts in a catalytic manner, yielding etch rates approximately one order of magnitude greater than those observed using inert masks. The essential role of the free radicals, originating from the peroxydisulfate ion, in the etching reaction is confirmed. The etching reaction is more rapid for more heavily n-type doped samples, and insulating C-doped layers act as an etch stop layer.