A-plane GaN hydride vapor phase epitaxy on a-plane GaN templates with and without use of TiN intermediate layers

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 individual grains close to 300-400 arc sec and halfwidth anisotropy with respect to sample rotation around the [11-20] direction.