Supersonic jet epitaxy of gallium nitride using triethylgallium and ammonia
Gallium nitride (GaN) films were grown on GaN(0001)/AlN/6H-SiC composite substrates at 700-780 degreesC by supersonic jet epitaxy using triethylgallium (TEG) and NH3. TEG was seeded in He and N-2 supersonic free jets to obtain kinetic energies of similar to2.1 and similar to0.5 eV, respectively, and NH3 was supplied from a variable leak valve. Higher TEG beam intensities (by about a factor of 5) were obtained by seeding in He. In situ reflection high-energy electron diffraction indicated a transition from three-dimensional to two-dimensional (2D) growth between 730 and 750 degreesC for films grown using TEG seeded in He and a constant NH3/TEG flux ratio. Ex situ atomic force microscopy of films grown at 730 and 750 degreesC revealed smooth surfaces comprised of quasi-2D islands with irregular perimeters. Cross-sectional transmission electron microscopy evidenced that the film grown at 750 degreesC was homoepitaxial alpha-GaN with a high density of planar lattice defects. Secondary ion mass spectrometry detected high residual carbon concentrations in the films. The GaN growth rate at 750 degreesC was found to depend on TEG flux and NH3 pressure in a manner consistent with Langmuir-Hinshelwood kinetics. Films grown under NH3-rich conditions were faceted and microscopically rough, whereas nonfaceted, basal-plane growth was observed under Ga-rich conditions. The first-order dependence of growth rate on TEG flux under NH3-rich conditions was used to estimate Ga incorporation efficiencies for high- and low-energy TEG beams. The Ga incorporation efficiency is lower for high-energy TEG beams, consistent with a decrease in the sticking coefficient for dissociative chemisorption. (C) 2003 American vacuum Society.