Photo-Enhanced Acid Chemical Etching of High-Quality Aluminum Nitride Grown by Metal-Organic Chemical Vapor Deposition

Photo-enhanced chemical (PEC) etch of wurtzite aluminum nitride (AlN) was investigated to overcome its low etch rate. Epitaxial AlN grown on Al2O3 substrate by metal-organic chemical vapor deposition method was immersed in phosphoric acid at different temperatures under 185 nm deep-UV excitation. An inverted pyramid structure with {10-1-1} faces initially appeared, after chemical etching, evolving into hexagonal columns with {1-100} m-planes. The PEC etch rate of m-plane AlN was six-fold higher than that of non-PEC one because the reaction was enhanced by the electron-hole pairs photo-generated by 185 nm wavelength. The decrease of the activation energy from 68.5 kJ/mol (non-PEC etch) to 48.1 kJ/mol (PEC etch) was extracted, implying a reaction-limited etching process. The PEC etch mechanism of wurtzite AlN in phosphoric acid was proposed, including the initiation and growth of the etch pit and the agglomeration of the hexagonal columns. Our results propose a facile method to control the surface morphology of AlN-based electronic and optoelectronic devices.