Magnetron sputter epitaxy of gallium nitride on (0001) sapphire

This paper reports the growth and characterisation of Gallium Nitride epilayers on(0001)sapphire using the technique of Magnetron Sputter Epitaxy(MSE). The technique employs a solid gallium sputter target and ammonia as the reactive nitrogen source. Epilayers with good crystallinity were deposited at 900 degrees C using a 500 Angstrom GaN buffer layer grown at 550 degrees C. Triple axis xray studies indicated a high degree of crystal perfection with a mosaic structure resulting from low angle tilts between crystal grains. Transmission electron microscopy (TEM) studies showed epitaxial films with a columnar structure. Growth rates were typically >0.3 mu m/hr, limited by the gallium flux (target power). Strong band edge photoluminescence (at 3.48 eV) was observed due to donor bound exciton emission with only weak emission from the lower energy (2.2 eV) defect band. Raman measurements showed sharp peaks due to the A(1)(TO), E-1(TO), E-2 and A(1)(LO) lattice vibrational modes of GaN, closely matching the single crystal spectra. Doping studies using silane have shown that carrier densities in the range of 10(17)-->10(20) cm(-3) can be obtained.