Oxynitride mediated epitaxy of gallium nitride on silicon(1 1 1) substrates in a merged hydride/metal-organic vapor phase epitaxy system

A technique was developed to deposit GaN on a Si(1 1 1) substrate by a four-step process in a single reactor: formation of ultra-thin oxide, conversion to an oxynitride via NH3 exposure at the onset of growth, low-temperature MOCVD of GaN, followed by HVPE of GaN. It was found that this oxynitride compliant layer served to relieve stress at the GaN/Si interface as well as protect the Si substrate from reaction with free Ga atoms present during the initial stages of growth and interfacial reactions with the adjoining GaN film. Electron microscopy revealed that an ultra-thin (less than 2 nm) oxynitride could maintain the hexagonal epitaxial relationship of the Si substrate allowing growth of single crystal GaN. It was shown experimentally that formation of a thicker oxynitride layer was detrimental to GaN epitaxy due to loss of the epitaxial relationship. In the final HVPE step, single crystal GaN films were deposited from a traditional growth temperature of 950 down to 560 °C which is the lowest reported temperature for VPE of single crystal GaN. The unique reactor configuration allowed the HVPE process to initiate on a pristine MOCVD GaN surface. Additionally, epitaxy at low temperature was achievable due to the presence of free HCl which suppresses the formation of energetically unstable nuclei.