Review of pendeo-epitaxial growth and characterization of thin films of GaN and AlGaN alloys on 6H-SiC(0001) and Si(111) substrates

Discrete and coalesced monocrystalline GaN and AlxGa1-xN layers grown via p endeo-epitaxy (PE) originated from side walls of GaN seed stripes with and without SiNx top masks have been grown via organometallic vapor phase depos ition on GaN/AlN/6H-SiC(0001) and GaN( 0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to ev aluate the external microstructures and the distribution of dislocations, r espectively. The dislocation density in the laterally grown sidewall region s and in the regions grown over the SiNx masks was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting of 0. 2 degrees in the coalesced GaN epilayers grown over the SiNx masks was dete rmined via X-ray and selected area diffraction; however, tilting was not ob served in the material suspended above the SiC substrate and that grown on unmasked stripes. A strong, low-temperature photoluminescence band-edge pea k at similar to3.45 eV with a FWHM of <300 eV was determined on the overgro wth material grown on the silicon carbide substrates. The band-edge in the GaN grown on silicon substrates was shifted to a lower energy by 10 meV, in dicative of a greater tensile stress.