Effect of sapphire nitridation on GaN by MOCVD

Efficiency and lifetime of light emitting diodes and laser diodes inversely depend on defect density of the crystal. Reduction of defect density is accomplished by proper choice of the substrate or deliberate modification of substrate surface. Roughness of substrate surface for GaN deposition can be controlled by buffer growth and/or nitridation. Buffer layers or nitrided layers promote lateral growth of films due to decrease in interfacial free energy between the film and substrate. Optimum conditions for nitridation and GaN-buffer growth on Al₂O₃(0001) were determined by means of atomic force microscopy (AFM). AFM analysis of nitridated sapphire surfaces was also carried out to find the optimum condition for nitridation of sapphire substrate before GaN-buffer layer deposition. Nitridation of sapphires was performed only with nitrogen. Based on the fact that GaN deposited on modified surface exhibited the better crystal quality and optical property, use of AFM roughness as a reliable criterion is suggested for process optimization of GaN film growth by metallorganic chemical vapor deposition.