Improved quality GaN films grown by molecular beam epitaxy on sapphire

Abstract
We report on the epitaxial growth and characterization of gallium nitride by molecular beam epitaxy (MBE). The samples were grown on (0002) sapphire using solid metal group III sources and an EPI UniBulb™ rf plasma source to produce atomic neutral nitrogen species. The films were characterized optically using reflectance and photoluminescence, van der Pauw Hall effect measurements, and x-ray rocking curves for the (0002), (101̄4), and (22̄04) directions. Nominally undoped films were grown with a (0002) rocking curve (ω) full width at half maximum (FWHM) from 700 to 125 arcsec, electron mobilities of up to 180 cm2/V s, and background carrier concentrations from the mid- 1017–2×1016/cm3. The room temperature photoluminescence FWHM for these films ranged from 38 up to 62 meV, with peak to yellow ratios from 7 to 70. These values represent an improvement in the quality of nominally undoped heteroepitaxially grown GaN by MBE.