Role of energy-band offset in photo-electrochemical etching mechanism of p-GaN heterostructures

For developing p-GaN gate-based enhancement-mode AlGaN/GaN high-electron-mobility transistors, the removal of the p-GaN layer around the gate region is demonstrated by photo-electrochemical etching. The etching behavior of p-GaN/AlGaN/GaN heterostructures along with p-GaN/u-GaN reference samples is investigated in acidic H2SO4/H3PO4 electrolyte solution. The strong oxidant sulfate radical SO 4 − ∗ formed by H2SO4 stimulates the etching process by either extracting excess electrons from the valence band or providing supplementary holes in the valence band. By optimizing the etching parameters, an average etching rate of 0.27 nm/min with a surface roughness of 2.3 nm is achieved for removing p-GaN from the AlGaN/GaN structure. The etching dynamics of the heterostructure are attributed to the valence-band offset ΔEv caused by band discontinuity at the p-GaN/AlGaN interface. Under positive anodic bias, the etching process is also controlled by local charge transport between p-GaN and the two-dimensional electron gas channel due to a reduced barrier height.