Accession Number : ADA338206

Title :   Selected Energy Epitaxial Deposition and Low Energy Electron Microscopy of AlN, GaN, and SiC Thin Films

Descriptive Note : Quarterly technical rept. 1 Oct-31 Dec 97

Corporate Author : NORTH CAROLINA STATE UNIV AT RALEIGH

Personal Author(s) : Davis, R. F. ; Lamb, H. H. ; Tsong, I. S. ; Bauer, E. ; Chen, E.

PDF Url : ADA338206

Report Date : DEC 1997

Pagination or Media Count : 30

Abstract : LEEM/LEED studies were conducted on 6H-SiC(0001) substrates etched in different environments including: (a) pure hydrogen at atmospheric pressure at 1600 C; (b) a mixture of HC1 and hydrogen at 1350 deg C; and (c) a mixture of 5% hydrogen in atmospheric helium at 1600 deg C. Substrates with reasonable stepped structures and suitable for in situ LEEM studies of nitride film growth were obtained after using technique (c). Effective dissociation and adsorption mechanisms during the impact of ammonia molecules on the polar and nonpolar surfaces of GaN were identified by analyzing trajectories obtained from short period molecular dynamics simulations. The co adsorption of NH2 and H is exothermic for the case where NH2 binds to cation dangling bonds and H binds to anion dangling bonds of the surface. The energy barrier for the dissociative adsorption of ammonia on the GaN(0001(bar)) surface is estimated to be smaller than 0.5 eV. It was also determined that ammonia physisorbs on this surface at low kinetic energies (i.e. 0.031-0.061 eV). Dissociative chemisorption is initiated with increasing kinetic energy. For kinetic energies greater than 0.33 eV, the growth rate remains constant suggesting that the barrier for dissociative chemisorption has been overcome. From these observations it is proposed that the barrier height is approximately 0.3 +/- 0.1 eV. Preliminary results suggest that AIN films grown on hydrogen etched SiC substrates are superior to those grown on as received SiC substrates. Homoepitaxial growth of GaN on OMVPE-grown GaN/AIN/SiC substrates was accomplished using a NH3-seeded supersonic molecular beam and Ga effusion cell. Gallium limited growth kinetics were observed at 730 and 770 deg C for incident Ga fluxes less than or equal 1.2 x 10 to the minus 15th power sq. cm s-1 using a 0.25 eV NH3 beam.

Descriptors :   *ALUMINUM COMPOUNDS, *THIN FILMS, *EPITAXIAL GROWTH, *NITRIDES, *ELECTRON MICROSCOPY, *LOW ENERGY, *SILICON CARBIDES, *GALLIUM COMPOUNDS, KINEMATICS, ELECTRONICS, OPTICS, MOLECULES.

Subject Categories : Inorganic Chemistry
      Physical Chemistry

Distribution Statement : APPROVED FOR PUBLIC RELEASE