Investigation of dislocation density of GaN with single- and double-buffer layer grown on sapphire (0001) by RF-plasma assisted MBE

The two-dimensional growth and dislocation density of GaN epi-layer were studied by using single-buffer layer (SBL) and double-buffer layers (DBLs) grown on sapphire (0001) by radio frequency plasma assisted molecular beam epitaxy (RFP-MBE). The DBLs consist of two buffer layers deposited at two different temperatures T1 and T2 (T2>T1), and the high temperature annealing was performed after the buffer layer growth at T1. The surface morphology was observed by atomic force microscope (AFM), and the two-dimensional growth of GaN epi-layer was characterized by ω-scan rocking curve of X-ray diffraction (XRD). It was found that the rms (root-mean-square) roughness was decreased obviously and the full-width at half maximum (FWHM) of ω-scan rocking curve was reduced drastically when the GaN DBLs were used. The dislocation density of the GaN epi-layer grown on DBLs, which was estimated by two-dimensional triple axes mapping (TDTAM) of XRD measurement, was only a half as compared with that grown on SBL. It was shown that the quality of GaN epi-layer was improved by using DBLs.