Improvement of crystal quality of GaN grown on AlN template by MOCVD using HT-AlN interlayer

Two GaN samples, with and without high temperature (HT)-AlN interlayer (labelled as sample A and B, respectively) grown by MOCVD on AlN template, were investigated by double-crystal X-ray diffraction (DC-XRD), photoluminescence (PL), and atomic force microscope (AFM) measurements. It was found that the crystal quality of GaN could be greatly improved by the HT-AlN interlayer. The full width at half maximum (FWHM) of (102) reflection in XRD rocking curve was narrower for sample A than that for sample B. However, the FWHMs of (002) reflections were almost the same for the two samples. In addition, the tilt degree which reflected screw dislocation density was almost the same, while the twist degree which reflected edge dislocation density changed from 0.214 degrees to 0.152 degrees when the HT-AlN interlayer was used. Both the intensities of (102) reflection in XRD and band edge emission in PL for sample A were stronger too. In the AFM images, the atomic growth steps of sample A were clearer than those of sample B. According to the results of the in situ optical reflectivity spectra and the atomic force microscope (AFM) images, the above results were attributed to the three-dimensional (3D) growth mode of the HT-AlN interlayer. The HT-AlN interlayer may work as a kind of "micro-area" seed for epitaxial lateral overgrowth (ELOG) resulting in bending some dislocations. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim