ABSTRACTElectron Cyclotron Resonance Plasma Assisted Molecular Beam Epitaxy (ECR-MBE) and Gas Source Molecular Beam Epitaxy (GSMBE) have been used to grow hexagonal GaN on Si (111). In the ECR-MBE configuration high purity nitrogen has been used as nitrogen source. In GSMBE ammonia was supplied directly to the substrate to be thermally cracked in the presence of gallium.By a combined application of in-situ reflection high-energy electron-diffraction (RHEED) and cross-sectional transmission electron microscopy (TEM) the growth mode and structure of GaN were determined. The growth mode strongly depends on growth conditions. Quasi two dimensional growth was observed in ECR-MBE configuration for a substrate temperature of 640°C while three dimensional growth occured in GSMBE configuration in the temperature range from 640 to 800°C.Low temperature (9 K) photoluminescence spectra show that for samples grown by ECR-MBE and GSMBE a strong near band gap emission peak dominates while transitions due to deep level states are hardly detectable. The best optical results (the highest near band gap emission peak intensity) have been observed for samples grown by GSMBE at high temperature (800°C). This could be explained by the increase of grain dimensions (up to 0,3 – 0,5 μm) observed in samples grown by GSMBE at 800°C.
