Study on Sapphire Surface Preparation for III-Nitride Heteroepitaxial Growth by Chemical Treatments

The etching of sapphire substrates using and a 3:1 mixture, as a function of temperature and etching time, was systematically studied using atomic force microscopy. The sapphire preparation by liquid-based etchings was compared with etching at 1100°C and air-annealing at 1400°C. In liquid-based treatments, the smoothest, pit-free surface was obtained by etching in pure at 300°C for 30 min. Sulfuric acid etching at higher temperatures or for longer periods generated an insoluble mixture of and crystalline deposits on the surface. Phosphoric acid and the 3:1 mixture, which is the routinely employed chemical treatment for sapphire preparation, etched the sapphire preferentially at defect sites and resulted in pit formation on the surface. Sapphire treatment using at 1100°C did not remove the surface damage. Air annealing the sapphire at 1400°C for 1 h produced an atomically smooth surface consisting of a terrace-and-step structure. The results of this study were described in terms of the chemistry of the sapphire etching process. © 2002 The Electrochemical Society. All rights reserved.