We report on the plasma-assisted molecular-beam epitaxy of Mg-doped ͑1010͒ GaN on ͑1010͒ 6H-SiC. Secondary ion mass spectroscopy measurements show the incorporation of Mg into the GaN films with an enhanced Mg incorporation under N-rich conditions relative to Ga-rich growth. Transport measurements of Mg-doped layers grown under Ga-rich conditions show hole concentrations in the range of p =1ϫ 10 18 to p =7ϫ 10 18 cm −3 and a dependence between hole concentration and Mg beam equivalent pressure. An anisotropy in in-plane hole mobilities was observed, with the hole mobility parallel to ͓1120͔ being higher than that parallel to ͓0001͔ for the same hole concentration. Mobilities parallel to ͓1120͔ were as high as ϳ11.5 cm 2 /Vs ͑at p ϳ 1.8 ϫ 10 18 cm −3 ͒.

A model of basal plane stacking faults as boundaries between incoherently scattering domains in m-plane GaN films is reviewed. m-Plane GaN films are analyzed with a modified version of the Williamson-Hall analysis in order to determine the length-scale of coherent scattering and tilt-mosaic contribution to X-ray rocking curve widths for the primary in-plane directions. This analysis shows that basal plane stacking faults are the predominant source of rocking-curve width anisotropy in the m-plane films, and indicate that the modified Williamson-Hall analysis can be used as a non-destructive technique for measuring basal plane stacking fault densities in m-GaN films.

Plasma-assisted molecular beam epitaxial growth of Mg-doped, p-type and Si-doped, n-type m-plane GaN on 6H m-plane SiC is demonstrated. Phase-pure, m-plane GaN films exhibiting a large anisotropy in film mosaic ͑ϳ0.2°full width at half maximum, x-ray rocking curve scan taken parallel to ͓1120͔ versus ϳ2°parallel to ͓0001͔͒ were grown on m-plane SiC substrates. Maximum hole concentrations of ϳ7 ϫ 10 18 cm −3 were achieved with p-type conductivities as high as ϳ5 ⍀ −1 cm −1 without the presence of Mg-rich inclusions or inversion domains as viewed by cross-section transmission electron microscopy. Temperature dependent Hall effect measurements indicate that the Mg-related acceptor state in m-plane GaN is the same as that exhibited in c-plane GaN. Free electron concentrations as high as ϳ4 ϫ 10 18 cm −3 were measured in the Si-doped m-plane GaN with corresponding mobilities of ϳ500 cm 2 / V s measured parallel to the ͓1120͔ direction.

Ammonothermal GaN growth using a novel apparatus has been performed on c-plane, m-plane, and semipolar seed crystals with diameters between 5 mm and 2 in. to thicknesses of 0.5-3 mm. The highest growth rates are greater than 40 m/h and rates in the 10-30 m/h range are routinely observed for all orientations. These values are 5{100Â larger than those achieved by conventional ammonothermal GaN growth. The crystals have been characterized by X-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), optical spectroscopy, and capacitance-voltage measurements. The crystallinity of the grown crystals is similar to or better than that of the seed crystals, with FWHM values of about 20-100 arcsec and dislocation densities of 1 Â 10 5-5 Â 10 6 cm À2. Dislocation densities below 10 4 cm À2 are observed in laterally-grown crystals. Epitaxial InGaN quantum well structures have been successfully grown on ammonothermal wafers.

Transport measurements of p‐type m ‐plane GaN films grown on low extended‐defect density, free‐standing m ‐plane (10$ \bar 1 $0) GaN substrates are presented. No significant anisotropy in in‐plane mobility was found for hole concentrations between 2.45 × 1017 and 8.7 × 1018 cm–3. Since faulted, heteroepitaxial m ‐plane films showed significant anisotropy in electron and hole mobility a microstructural feature with anisotropic distribution (basal plane stacking faults) is discussed as a possible source of anisotropic scattering in non‐polar and semi‐polar films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)