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

Abstract

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 ∼4.2 × 108 cm−2 and ∼5 × 105 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 8 K and the deep level related yellow band emission ∼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.