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Thick a-plane GaN films were grown by hydride vapor phase epitaxy on a-plane GaN templates prepared by metalorganic chemical vapor deposition (MOCVD) and also on a-plane MOCVD templates using in situ nitridized Ti underlayers. The growth on a-GaN showed improved crystalline quality with increasing hydride vapor phase epitaxy thickness, while MOCVD template quality had little effect. With 30 nm Ti films deposited on the templates and converted to TiN islands by nitridation during growth, the authors obtained thick (350 μm), freestanding a-GaN films detached from the template. Microcathodoluminescence spectra of the growth surface showed intense band edge luminescence at 3.47 eV at 90 K with no defect bands. Spectra taken from the surface turned to the substrate were dominated by stacking fault-related bands at 3.42, 3.3, and 3.0 eV, similar to the spectra of the a-GaN templates. X-ray measurements showed the freestanding a-GaN layers consisted of misoriented large grains of a-GaN with halfwidth for individ...

Growth of GaN on polycrystalline chemical vapor deposition (CVD) diamond prepared on Si was achieved by hydride vapor phase epitaxy (HVPE). If the polycrystalline CVD diamond is separated from the Si substrate and the side turned to Si is covered by either TiN or anodic Al oxide, this is found to facilitate deposition of good crystalline quality GaN films. Porous TiN in these experiments was formed by Ti evaporation and subsequent in situ nitridation in the HVPE reactor during pregrowth heating. The films showed double crystal x-ray (0002) rocking curve half width of 245 in. and a strong bandedge luminescence. Thick films self-separated from the substrate. When growing GaN on the Si side of the diamond substrate is covered with porous Al anodic oxide, the authors observed the formation of well defined (0001) GaN texture with the maximum angle between the c-axes of various grains lower than 6.5°, a very low (120 in.) half-width of the (0002) rocking curves of individual grains and an intense bandedge lumin...

Nonpolar a-GaN films were grown by hydride vapor phase epitaxy on r-sapphire. As the thickness of the grown films was increased from 50 to over 250μm, the width of the double-crystal rocking curve for the (11–20) reflection decreased from 2000to500arcsec, indicating a strong decrease in the dislocation density. Microcathodoluminescence mapping of the thick films suggests that the dislocation density is ∼102cm−2, which is more than two orders of magnitude lower than for thin films. The authors also observe a corresponding decrease in the density of residual donors from 1020to1018cm−3, with respective mobility increase from (10–20) to 150cm2∕Vs. The luminescence spectra of the thin films show the presence of intense defect bands attributed in literature to stacking faults. These bands are very strongly suppressed in thick films, which also show about an order of magnitude higher band edge luminescence intensity.