An ~800 mm thick HVPE film deposited on an (0001) epi-ready Ammono substrate (~0.3 degree toward “m”) was removed from the reactor and its surface was chemical-mechanically polished (CMP). This template was put back in the HVPE reactor and an additional ~800 mm was deposited. The final crystal consisted of two sequentially grown HVPE-GaN layers on the Ammono substrate. The top HVPE layer was sliced off and three samples were diced from different regions of this wafer. The surfaces of these samples were mechanically polished and CMP finished. A combination of techniques was employed to investigate the structural, optical, and electrical properties of the crystals.
High resolution XRD was measured on two samples using a Rigaku Smartlab diffractometer with a four bounce Ge (220) monochromator. Lattice parameters were measured using symmetric and asymmetric scans: sample A: c=5.1856Å and a=3.1824Å; sample B were, c=5.1856Å and a=3.1839Å. These values are very close to the bulk lattice constants. The rocking curves for these samples were measured and had full widths at half maximum of ~16 arcsecs, indicating superior crystalline quality.
High lateral and depth resolution micro-Raman scattering (RS) measurements were carried out on the front and back surfaces of two samples. The E22 phonon frequency was mapped on both faces of two samples; the distribution of Raman shifts was 567.45±0.05 cm-1, indicating stress free GaN. The A1(LO) phonon frequencies and the linewidths measured on the Ga-polar face were larger than those measured on the N-polar face; this is consistent with a larger incorporation of donor impurities as the growth proceeds. Low temperature, high spectral resolution photoluminescence (PL) measurements carried out on the Ga- and N-polar faces of these samples were also consistent with more doping as the growth proceeds . SIMS depth profile measurements also confirm this observation. Hall measurements provided information about the free-carrier concentration and carrier mobility.
 T. Sochacki, et al., J.J. Appl. Phys., 53 (2014) 05FA04.
 J.A. Freitas, Jr., et al., Cryst. Growth & Design, 15 (2015) 4837.