Growth of gallium nitride and aluminum gallium nitride thin films using conventional and pendeo-expitaxial growth processes on hydrogen(6)-silicon carbide(0001) and silicon(111) substrates

Pendeo-epitaxy (PE) of individual GaN and Al_xGa_1−x N films and single- and multi-layer heterostructures of these materials with low densities of dislocations and without coalescence boundaries have been achieved on striped GaN seed layers previously grown on AlN/6H-SiC (0001) substrates using metallorganic chemical vapor deposition (MOCVD). A reduction in the dislocation density of approximately five orders of magnitude was achieved in the laterally grown regions between the GaN stripes. The RMS roughness of the (112¯0) side wall of the uncoalesced areas of GaN was 0.099 nm. The application of a mask on the [11¯00] oriented GaN stripes hindered the vertical propagation of threading dislocations during regrowth; however, it also caused tilting in the moving fronts and associated crystallographic misregistry in the areas of coalescence over the stripes as well as the generation of dislocations propagating from the resulting boundaries. All of these problems were eliminated by the exclusion of the masks, as determined via X-ray diffraction and scanning and transmission electron microscopies. A comparative study of fully coalesced PE-Al_xGa_1−xN films with conventionally grown Al_xGa_1−xN films was conducted using scanning electron microscopy, X-ray diffraction (XRD), and high resolution scanning Auger microprobe analysis. An XRD FWHM of 794 arcsec was measured for PE-Al ₁₀Ga₉₀N films; this is comparable to conventionally grown films on these substrates. A variation of 1% in the atomic Al content of the Al₁₀Ga₉₀N films was determined to be related to the position in the microstructure.; Films of PE-GaN and PE-Al_xGa_1−xN were also grown on Si(111) substrates via the use of an intermediate 3C-SiC transition layer capped by a high-temperature AlN(0001) buffer layer. The 3C-SiC transition layer eliminated chemical reactions between the Si and the NH₃ and between the Si and Ga metal derived from the decomposition of triethylgallium. A similar reduction in the dislocation density in the regions between the stripes as well as tilting in the regions of the GaN epilayers that coalesced over the masks were again obtained. The latter problem was again solved by the removal of the mask. The strong, low-temperature PL band-edge peak at 3.456 eV with a FWHM of 17 meV was comparable to that observed in PE-GaN films grown directly on AlN/6H-SiC(0001) substrates.; An AlN transition layer has been investigated as a second approach for the growth of GaN on Si(111) substrates using MOCVD. The films microcracked along {lcub}11¯00{rcub} planes upon cooling. AlGaN/GaN heterostructures were grown using similar conditions. Room temperature Hall mobilities of 500 cm2/Vs were measured in crack free areas.