NUCLEATION AND GROWTH OF CHEMICAL BEAM EPITAXY GALLIUM NITRIDE THIN-FILMS

Gallium nitride films have been grown on (0001) sapphire substrates by chemical beam epitaxy (CBE) using triethyl gallium (TEG) and ammonia (NH3) precursors. Prior to the CBE epi-GaN layer growth, electron cycl otron resonance plasma-assisted metal-organic molecular beam epitaxy w as utilized to deposit a nucleation layer at lower temperatures. The c rystallinity of CBE-grown GaN films was found to be strongly growth-te mperature dependent. The degree of crystallinity was correlated with t he surface carbon composition as measured in situ by mass spectroscopy of recoiled ions. The optimum growth-temperature range for CBE GaN gr owth was found to be between 800 and 825 degrees C. Within this narrow window, thin films with streaky two-dimensional reflection high-energ y electron diffraction patterns and good photoluminescence properties were obtained. The surface rms roughness, as measured by atomic force microscopy, was as low as 40 Angstrom/l mu m(2) for the highest qualit y thin films lattice-resolved images supported the deposition of cryst alline GaN revealing hexagonal structures with the spacing anticipated for GaN. (C) 1997 American Institute of Physics.