Morphology and luminescence of porous GaN generated via Pt-assisted electroless etching

Porous gallium nitride (PGaN) is produced by Pt-assisted electroless etching of GaN. Ultrathin Pt films are sputtered onto the surface of GaN, and etching is carried out in a 1:2:1 or 1:2:2 solution of CH3OH:HF:H2O2. Etching proceeds by first forming a network of small pores, after which ridge structures form, with the porous network in trenches between the ridges. As the etch progresses further the sidewalk of the ridges become steeper, and then the ridges start to disappear. Cathodoluminescence (CL) spectroscopy and imaging show the ridges to be optically inactive, suggesting that the ridges might arise from grain boundaries or dislocations present ins the starting GaN material. CL emission is confined to the porous areas between the ridges. CL properties of the PGaN vary depending on the source of the original, nonporous GaN material. Undoped and unintentionally doped hydride vapor phase epitaxy materials produce PGaN which shows only band gap emission at 368 nm before and after etching, whereas PGaN produced from the Si-doped metalorganic chemical vapor deposited material exhibits two blueshifted luminescence bands at 358 and 326 nm. The origin of the 358 nm blueshifted emission can plausibly be explained by quantum confinement effects, but the 326 nm band can only be explained by other mechanisms, such as the creation of specific surface states by etching. The etched morphology is very similar among the different types of GaN substrates used, however the difference in light emission properties must be ascribed to growth conditions, or to the nature and concentration of the dopants. (C) 2002 American Vacuum Society.