MOLECULAR-BEAM EPITAXY GROWTH AND PROPERTIES OF GAN, ALXGA1-XN, AND ALN ON GAN SIC SUBSTRATES/

The thin him growth of GaN, AlGaN, and AlN on GaN/SiC substrates by mo lecular beam epitaxy (MBE) has been studied. The GaN/SiC substrates co nsisted of 3-mu m-thick GaN buffer layers grown on 6H-SiC wafers by me tal organic vapor phase epitaxy (MOVPE) at Cree Research, Inc. A radio frequency plasma source was employed to generate active nitrogen spec ies for MBE growth. The high quality of the MBE grown GaN epilayers wa s evident from the intense room temperature photoluminescence (PL) dom inated by a sharp band-edge peak at 3.409 eV having a full width at ha lf maximum (FWHM) of 29.7 meV and the double-crystal x-ray rocking cur ve (0002) diffraction peak having FWHM as narrow as 156 arcsec. Vertic al cross-section TEM clearly showed these MBE grown GaN epilayers to h ave replicated the quality of the underlying MOVPE grown GaN buffer la yer on SIG. The room temperature PL spectra from Mg doped p-type films showed a dominant peak at 3.2 eV. AlxGa1-xN films were also grown on GaN/SiC substrates. Two-dimensional nucleation and growth was monitore d by reflection high energy electron diffraction for GaN, AlxGa1-xN, a nd AlN epilayer deposition, and featured (2 x 2) surface reconstructio n during the growth of GaN/AlN strained layer superlattices. Light emi tting diodes (LEDs) based on vertical AlxGa1-xN/GaN double heterostruc tures have been demonstrated for the first time using MBE grown III-V nitrides on conducting GaN/SiC substrate materials. The typical turn-o n voltage among these LEDs was 3.2 V. The forward bias voltage was 4.7 V at 20 mA. The peak wavelength of the electroluminescence (EL) spect rum was 400 nm at 77 K. These results demonstrate that MBE may be used to produce GaN, AlxGa1-xN and AlN based epitaxial structures which ar e comparable in crystalline quality to those grown by MOVPE. (C) 1996 American Vacuum Society.