Study on the initial stages of heteroepitaxial growth of hexagonal GaN on sapphire by plasma assisted MBE

We have studied several growth initiation processes for heteroepitaxial growth of hexagonal GaN on (0 0 0 1) sapphire substrates by molecular beam epitaxy using radio-frequency N-2 plasma. Based on the results of reflection high-energy electron diffraction, high-resolution X-ray diffraction and high-resolution transmission electron microscopy analyses, it was found that the nitridation process results in better structural quality of epilayers compared with the low-temperature buffer layer processes. By using nitrogen flux modulation during the initial period of main growth of GaN, very flat and smooth surfaces could be obtained. The best ever value of X-ray diffraction hull-width at the half-maximum value of 51 arcseconds for MBE grown hexagonal GaN epilayers on sapphire was achieved. (C) 1998 Elsevier Science B.V. All rights reserved.