Direct Growth of a-Plane GaN on r-Plane Sapphire by Metal Organic Chemical Vapor Deposition

In this study, we had demonstrated the direct growth of nonpolar a -plane GaN on an r -plane sapphire by metal organic chemical vapor deposition (MOCVD) without any buffer layer. First, in this experiment, we had determined the optimum temperature for two-step growth, including obtaining three-dimensional (3D) GaN islands in the nucleation layer and coalescing with a further two-dimensional (2D) growth mode. The result shows that the nucleation layer grown under high temperature (1150 °C) leads to large islands with few grain boundaries. Under the same temperature, the effect of the V/III ratio on the growth of the overlaying GaN layer to obtain a flat and void free a -plane GaN layer is also studied. The result indicates one can directly grow a smooth epitaxial layer on an r -plane sapphire by changing the V/III ratio. The rms roughness decreases from 13.61 to 2.02 nm. The GaN crystal quality is verified using a mixed acid to etch the film surface. The etch pit density (EPD) is 3.16 ×10 7 cm -2 .