Optoelectronic and Structural Properties of High-Quality GaN Grown by Hydride Vapor Phase Epitaxy

Gallium nitride (GaN) films have been grown by hydride vapor phase epitaxy (HVPE) in a vertical reactor design. We report on GaN growth directly on sapphire using a GaCl surface pretreatment. The electrical properties of these films compare favorably with the highest values reported in the literature for GaN. Specifically, a room temperature Hall mobility as high as 540 cm2/V·s, with a corresponding carrier concentration of 2×1017 cm-3, have been attained. Additionally, the vertical reactor design has assisted in reducing nonuniformities in both film thickness as well as in transport properties due to depletion effects, as compared with horizontal designs. The dislocation density in these films has been determined by plan-view transmission electron microscopy to be approx.3×108 cm-2. Photoluminescence spectra obtained at 2 K show intense, sharp, near-bandedge emission with minimal deep level emissions. Stimulated emission has been observed in these films, utilizing a nitrogen laser pump source (λ=337.1 nm) with a threshold pump power of approx.0.5 MW/cm2. These results suggest that HVPE is viable for the growth of high-quality nitride films, particularly for the subsequent homoepitaxial overgrowth of device structures by other growth methods such as OMVPE and MBE.