PHOTOELECTROCHEMICAL INVESTIGATION OF THE ETCHING OF GAN IN H_3PO_4

摘要

The photoelectrochemical (PEC) etching of GaN in H_3PO_4 has been studied both as a function of electrolyte pH and illumination intensity. Etching of GaN was found to occur in aqueous H_3PO_4 solutions ranging in concentration from 1.0 x 10~(-3) mol dm~(-3) to 5.0 mol dm~(-3). A peak etch rate of 3.6 nm s~(-1) was observed at a pH of 0.6. The reduced etch rate at lower pH is attributed to mass transport effects in the higher viscosity H_3PO_4 electrolyte and at higher pH it is attributed to the formation of a passivating oxide film. The illumination intensity dependence of the PEC etch rate was also investigated in the intensity range 5 mW cm~(-2) to 50 mW cm~(-2). Etch rates increased in a roughly linear manner with increasing light intensity. However, they saturated at light intensities greater than ～34 mW cm~(-2) indicating a diffusion-limited etching regime. SEM analysis of GaN anodized in 0.001 mol dm~(-3) H_3PO_4 revealed the presence of a cracked oxide film on the surface.