Nanoporous GaN by UV assisted electroless etching for sensor applications

grown by HVPE on sapphire. The samples were subjected to an etching procedure in order to induce the formation of pores. The etching was photo-assisted with a 365 nm UV light beam with power density up to 0.8 W/cm2 (Hamamatsu L9566-01), and directed on the sample using a quartz light guide and a collimator (Hamamatsu E5147-06). The etching was performed in an in-house made electrochemical chamber with an illumination window. In this work, no external bias was applied between the sample and the electrolyte. Prior to the etching, the GaN samples were cleaned in a standard organic procedure (hot 2-metil-pirrolidone followed by hot acetone and rinsed in methanol) and a 10% HF bath for 30 seconds. After the cleaning procedure some of the samples were covered with 3 nm thin platinum islands of different sizes. Different HF:H202 based electrolytes were investigated for this procedure using different concentrations and diluents (mainly H20 and CH3OH). SEM, PL and wetting angle measurements were performed in order to characterise the fabricated material. An He-Cd (above bandgap illumination with X = 325 nm) pumping laser was used for the PL measurements.