Growth and characterization of thin films and patterned substrates of III-V nitrides on SiC(0001) substrates

Monocrystalline GaN and Al_xGa_1-xN(0001) (0.05≤x≤0.96) thin films were grown at high temperatures via metallorganic vapor phase epitaxy (MOVPE) on α(6H)-SiC(0001) wafers. Use of a 1000 angstroms high temperature AlN buffer layer was employed for GaN deposition; the Al_xGa_1-xN was deposited directly on the substrate. Photoluminescence (PL) spectra of GaN showed bound and free excitonic recombinations. The compositions of the Al_xGa_1-xN films were compared to the values of the bandgap as measured by cathodoluminescence (CL), and a functional relationship determined. Selective growth of GaN has been achieved on GaN/AlN/6H-SiC(0001) multilayer substrates using an overlying SiO₂ layer containing circular and striped patterns. Uniform hexagonal pyramid arrays of undoped GaN and Si-doped GaN were achieved within the 5 μm circular patterns. Field emission measurements of these arrays exhibited a turn-on field of 25 V/μm for an emission current of 10.8 nA at an anode-to-sample distance of 27 μm. Lateral growth and coalescence over the SiO₂ masks have been achieved using stripes oriented along 〈11̄00〉 at 1100 °C and a triethylgallium flow rate of 26 μmol/min. A density of approximately 10⁹ cm^-2 threading dislocations, originating from the underlying GaN/AlN interface, were contained in the GaN grown in the window regions. The overgrowth regions, by contrast, contained a very low density of dislocations. The surfaces of the coalesced layers had a terrace structure and an average RMS roughness of 0.26 nm.