New pretreatment method of sapphire for GaN deposition

It has been confirmed that the reactive ion (N-2(+)) beam (RIB) pretreatmen t of the sapphire substrate at room temperature is an alternative pretreatm ent method. The chemical and physical status of RIB treated sapphire surfac e results in the etching of the surface and the formation of a very thin am orphous-like disordered AlON layer under the sapphire surface. The threadin g dislocation density of GaN on Al2O3(0001) with RIB pretreatment was decre ased due to the partial crystallization of the RIB layer during high temper ature main growth of GaN. The crystallized region may contribute to the pre ferential nucleation site for GaN, promoting the 2-D growth mode. In additi on, the remaining amorphous layer may absorb lattice strain originating fro m the lattice misfit between sapphire and GaN film. The optical properties of GaN films have improved with RIB pretreatment. Current observation clear ly shows that the RIB pretreatment of the sapphire surface can be used to i mprove the GaN films grown by metalorganic chemical vapor deposition (MOCVD ).