Gallium nitride films have been grown on (0001) sapphire substrates by chemical beam epitaxy (CBE) using triethyl gallium (TEG) and ammonia (NH↓(3)) precursors. Prior to the CBE epi-GaN layer growth, electron cyclotron resonance plasma-assisted metal-organic molecular beam epitaxy was utilized to deposit a nucleation layer at lower temperatures. The crystallinity of CBE-grown GaN films was found to be strongly growth-temperature dependent. The degree of crystallinity was correlated with the surface carbon composition as measured in situ by mass spectroscopy of recoiled ions. The optimum growth-temperature range for CBE GaN growth was found to be between 800 and 825℃. Within this narrow window, thin films with streaky two-dimensional reflection high-energy electron diffraction patterns and good photoluminescence properties were obtained. The surface rms roughness, as measured by atomic force microscopy, was as low as 40 (A)/l μm↑(2) for the highest quality thin films: lattice-resolved images supported the deposition of crystalline GaN revealing hexagonal structures with the spacing anticipated for GaN. # 1997 American Institute of Physics. S0003-6951 (97)03447-5
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