Homo-epitaxial growth of high crystal quality GaN thin films by plasma assisted-molecular beam epitaxy

Gallium nitride (GaN) films homo-epitaxially grown on GaN/sapphire templates and free standing GaN substrates by plasma-assisted molecular beam epitaxy (PA-MBE) have been investigated. After optimizations of growth temperature, the Ga/N flux ratio, surface preparation as well as initial growth process, the high quality MBE-GaN films were obtained. Combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements, the TD densities were measured similar to 4.2 x 10(8) cm(-2) and similar to 5 x 10(5) cm(-2) for MBE-grown GaN films grown on GaN/sapphire templates and free standing GaN substrates, respectively. The observations of TEM prove the clear interface and well-arranged atomic lattice between substrates and as-grown layers. Besides, a flat and smooth surface with step-flow growth mode is observed by atomic force microscopy (AFM). Photoluminescence (PL) measurements exhibit that the linewidth for free excitons is as narrow as 4 meV at low temperature of 8K and the deep level related yellow band emission similar to 550 nm have been effectively suppressed at room temperature. The process optimization and obtained results give us wide latitude to fabricate high performance devices with lower tolerance to dislocation density.