GaN homoepitaxy by metalorganic chemical-vapor deposition on free-standing GaN substrates

Lattice-matched GaN layers are grown by metalorganic chemical-vapor deposition on free-standing GaN substrates, which were fabricated by laser-induced liftoff of 300-mu m-thick films grown by hydride vapor-phase epitaxy. Pretreatment of the free-standing films before the homoepitaxial growth of GaN involved mechanical polishing of the Ga-face surface and a final Cl-based plasma etch. By a combination of high-resolution x-ray diffraction, atomic-force microscopy, as well as Raman and photoluminescence spectroscopy, the structural and optical properties of the lattice-matched GaN layers are characterized. X-ray diffraction patterns of (0002), (0004), and (0006) reflexes with a full width at half maximum (FWHM) of as low as 20 arcsec are obtained. The dislocation density is determined to be 2x10(7) cm(-2) and the surface morphology is dominated by bilayer steps with terraces of about 200 nm. The lattice mismatch between the GaN substrate and the homoepitaxial layer is below 3x10(-5), resulting in a very narrow FWHM of the excitonic luminescence of 0.5 meV. (C) 2000 American Institute of Physics. [S0003-6951(00)03238-1].