Crystallization of free standing bulk GaN by HVPE (original) (raw)
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Free-standing 2-inch bulk GaN crystal fabrication by HVPE using a carbon buffer layer
2019
A free-standing bulk gallium nitride layer with a thickness of 365 μm and a diameter of 50 mm was obtained by hydride vapor phase epitaxy on a sapphire substrate with a carbon buffer layer. The carbon buffer layer was deposited by thermal decomposition of methane in situ in the same process with the growth of a bulk GaN layer. The bulk GaN layer grown on the carbon buffer layer self-separated from the sapphire substrate during the cooling after the growth. The dislocation density was 8·10^6 cm^-2. The (0002) X-Ray rocking curve full width at half maximum was 164 arcsec.
Journal of Applied Physics, 2004
Crack-free bulk-like GaN with high crystalline quality has been obtained by hydride-vapor-phase-epitaxy ͑HVPE͒ growth on a two-step epitaxial lateral overgrown GaN template on sapphire. During the cooling down stage, the as-grown 270-m-thick GaN layer was self-separated from the sapphire substrate. Plan-view transmission electron microscopy images show the dislocation density of the free-standing HVPE-GaN to be ϳ2.5ϫ10 7 cm Ϫ2 on the Ga-polar face. A low Ga vacancy related defect concentration of about 8ϫ10 15 cm Ϫ3 is extracted from positron annihilation spectroscopy data. The residual stress and the crystalline quality of the material are studied by two complementary techniques. Low-temperature photoluminescence spectra show the main neutral donor bound exciton line to be composed of a doublet structure at 3.4715 ͑3.4712͒ eV and 3.4721 ͑3.4718͒ eV for the Ga-͑N-͒ polar face with the higher-energy component dominating. These line positions suggest virtually strain-free material on both surfaces with high crystalline quality as indicated by the small full width at half maximum values of the donor bound exciton lines. The E 1 (TO) phonon mode position measured at 558.52 cm Ϫ1 ͑Ga face͒ by infrared spectroscopic ellipsometry confirms the small residual stress in the material, which is hence well suited to act as a lattice-constant and thermal-expansion-coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications.
MRS Proceedings, 2001
ABSTRACTStructural, electrical and optical properties of free-standing 200-μm thick GaN films grown by hydride vapor phase epitaxy (HVPE) have been investigated. After laser lift-off, the GaN substrates were mechanically polished on both Ga and N-sides and dry etched only on the Ga- side to obtain a smooth epi-ready surface. Hot H3PO4 chemical etching on both surfaces was used to reveal the defect sites, which appeared as hexagonal pits. The etched surfaces were then examined by atomic force microscopy. A few seconds of etching was sufficient to smooth the N- face surface and produce etch pits with a density of ≈ 1×107 cm−2. In contrast, a 50 minute etching was needed to delineate the defect sites on the Ga-face which led to a density as low as 5×105 cm−2. From plan-view and cross-sectional transmission electron microscopy (TEM) analysis, we have estimated that the dislocation density is less than about 5×106 cm−2 and ≈ 3×107 cm−2 for the Ga and N-faces respectively. The full-width ...
MRS Proceedings, 1996
We report a structural analysis of GaN layers with thicknesses ranging from 10 μm to 250 μm which have been grown on sapphire substrates by halide vapor phase epitaxy (HVPE). The effect of growth rate during HVPE growth has also been examined. The growth was performed using GaCl and ammonia as reactants; growth rates in excess of 90 μm/hr have been achieved. The structural characteristics of these layers have been performed wit'i high resolution x-ray diffractometry. Longitudinal scans parallel to the GaN [0002] direction, transverse scans perpendicular to the [0002], and reciprocal space maps of the total diffracted intensity have been obtained from a variety of GaN layers. The transverse scans typically show broad rocking curves with peak breadths of several hundreds of arcseconds. In contrast, the longitudinal scans (or “θ/2θ scans”) which are sensitive only to strains in the GaN layers (and not their mosaic distributions) showed peak widths that were at least an order of mag...
It has been shown during the present study that the E-etching at elevated temperatures can be adopted for the dislocation etching in hydride vapor-phase epitaxy (HVPE) GaN layers. It has been found that the X-ray diffraction (XRD) evaluation of the dislocation density in the thicker than 6 μm epilayers using conventional Williamson-Hall plots and Dunn-Koch equation is in an excellent agreement with the results of the elevated-temperature E-etching. The dislocation distribution measured for 2-inch GaN-onsapphire substrate suggests strongly the influence of the inelastic thermal stresses on the formation of the final dislocation pattern in the epilayer.
Journal of Crystal Growth, 2009
The nucleation of HVPE GaN on misoriented sapphire substrates and the transition from the nucleation layer to an epitaxial film were investigated. After a KOH/NaOH eutectic etch of the approximately 45 mm thick GaN layer, grown on sapphire using a low temperature nucleation, high temperature epitaxy process, the cross-sections revealed columnar structures, up to roughly 1 mm above the sapphire substrate. Photoetching of the thick GaN layers revealed inhomogeneous defect distributions along the cross-sections, which appeared to be related to the numerous pinholes originating at the GaN/sapphire interface. We present a model explaining the formation of pinholes by the coalescence of the GaN nuclei during the epitaxial overgrowth.
High resolution X-ray diffraction and X-ray topography study of GaN on sapphire
Materials Science and Engineering: B, 1999
High resolution X-ray diffraction and X-ray topography study of GaN thin films, grown on sapphire (11.0) substrate by reduced pressure metalorganic vapor phase epitaxy (MOVPE) under various conditions, were performed. The strained lattice parameters, stress, misorientation and dislocation density of GaN films were estimated. The experimental stress compares well with the theoretical stress obtained from the difference in the thermal expansion coefficient between the film and substrate. The dislocation density was found to be highest in the thinner GaN film. It was also higher in the film without any buffer layer. For the same carrier concentration, the mobility of one of the film was lower than the other which could be due to the presence of higher dislocation density. Slip lines associated with dislocations, stacking faults, cellular structure of dislocations and double positioning boundaries were found in the X-ray topography from the GaN films.