Heteroepitaxy of Nonpolar and Semipolar GaN

Abstract

There has been increasing research interest in nonpolar and semipolar GaN for high brightness light-emitting diode (LED) and laser diode applications. Due to the very limited supply of GaN bulk substrates, the feasible way of obtaining cost-effective large-areanonpolar and semipolar GaN materials in the foreseeable future is still through heteroepitaxy on foreign substrates. The major challenge in the heteroepitaxy of nonpolar and semipolar GaN is the high density of stacking faults and partial dislocations, which are responsible for the poor performance of heteroepitaxial nonpolar and semipolar LEDs. This chapter presents kinetic Wulff plots (v-plots) of GaN as a novel and powerful methodology to understand and control GaN heteroepitaxy along various crystallographic orientations. Based on the v-plots, a two-step growth scheme is rationally designed and experimentally confirmed in reducing the defect density for nonpolar and semipolar GaN heteroepitaxy on planar substrates. A defect reduction model is proposed based on the correlation between the morphological evolution and the microstructural development. With the orientation of nucleation decoupled from the final film surface orientation, orientation controlled epitaxy has been demonstrated as a very promising approach for device quality nonpolar and semipolar GaN materials. The material research timeline of nonpolar and semipolar GaN is summarized and discussed.