Gallium Nitride Thick Films Grown by Hydride Vapor Phase Epitaxy

Gallium nitride (GaN) thick films (to 150 μm) have been deposited by hydride vapor phase epitaxy (HVPE). These films are unintentionally doped n-type (n = 1-2×1017 cm-3 at 300 K) and exhibit structural and electronic properties which are comparable with the best reported for GaN films grown by organometallic vapor phase epitaxy. Additionally, these properties are found to be uniform over 2-in diameter films grown on sapphire substrates. The use of either a GaCl or ZnO surface pretreatment has been found to substantially enhance the nucleation density, resulting in improved surface morphology and film properties, even though it appears that the ZnO film is thermochemically desorbed early on in the growth. Dislocation densities as low as approximately 5×107 cm-2 have been attained for films 40 μm thick. Homoepitaxial overgrowths both by electron-cyclotron-resonance plasma enhanced molecular beam epitaxy and OMVPE proceed in a straightforward manner, essentially replicating the defect structure of the HVPE GaN film.