New pretreatment method of sapphire for GaN deposition

It has been confirmed that the reactive ion (N₂⁺) beam (RIB) pretreatment of the sapphire substrate at room temperature is an alternative pretreatment method. The chemical and physical status of RIB treated sapphire surface results in the etching of the surface and the formation of a very thin amorphous-like disordered AlON layer under the sapphire surface. The threading dislocation density of GaN on Al₂O₃(0001) with RIB pretreatment was decreased due to the partial crystallization of the RIB layer during high temperature main growth of GaN. The crystallized region may contribute to the preferential nucleation site for GaN, promoting the 2-D growth mode. In addition, the remaining amorphous layer may absorb lattice strain originating from the lattice misfit between sapphire and GaN film. The optical properties of GaN films have improved with RIB pretreatment. Current observation clearly shows that the RIB pretreatment of the sapphire surface can be used to improve the GaN films grown by metalorganic chemical vapor deposition (MOCVD).