HIGH-QUALITY GAN GROWTH ON (0001)SAPPHIRE BY ION-REMOVED ELECTRON-CYCLOTRON-RESONANCE MOLECULAR-BEAM EPITAXY AND FIRST OBSERVATION OF (2X2)AND (4X4) REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION PATTERNS

GaN layers are grown on (0001) sapphire substrate by electron cyclotro n resonance molecular beam epitaxy (ECR-MBE) using an ECR plasma cell with ion removal magnets on the cell top for the nitrogen source. The efficiency of the ion removal magnets in this ECR plasma cell is 99%. High-quality GaN layers are obtained. In particular, (2x2) and (4x4) R HEED (reflection high-energy electron diffraction) patterns are observ ed during GaN growth and during cooling after growth, respectively, in dicating a flat and smooth surface of GaN. These results show the supe riority of the ion-removed ECR plasma cell.