AVS 45th International Symposium
    Selected Energy Epitaxy Topical Conference Thursday Sessions
       Session SE-ThA

Invited Paper SE-ThA1
Selected Energy Epitaxial Deposition of GaN and AlN on SiC(0001) Using Seeded Supersonic Free-Jets of NH@sub 3@ in Helium

Thursday, November 5, 1998, 2:00 pm, Room 327

Session: Seeded Supersonic Beam Epitaxial Growth
Presenter: R.B. Doak, Fulbright Senior Scholar, Ruhr-Universitaet-Bochum, Germany
Authors: V.M. Torres, Arizona State University
R.B. Doak, Fulbright Senior Scholar, Ruhr-Universitaet-Bochum, Germany
B.J. Wilkens, Arizona State University
David J. Smith, Arizona State University
I.S.T. Tsong, Arizona State University
Correspondent: Click to Email
By expanding a gas mixture into vacuum through a supersonic nozzle, a heavy "seed" species in a light diluent can be aerodynamically accelerated to suprathermal translational energies, tunable by adjusting the mixture and temperature of the nozzle. Such "seeded" beams retain the high intensity, directionality, and narrow energy distribution characteristic of a supersonic free-jet. They thus offer promise in selectively promoting specific gas-surface reactions, a matter of much current interest in the growth of III-N semiconductor thin films. We report the use of 10% NH@sub 3@ in He seeded beams to grow GaN and AlN epitaxially on 6H-SiC(0001) and to grow GaN on AlN buffer layers deposited on SiC(0001). The substrate temperature was 800° C in all cases and the incident NH@sub 3@ translational energy was varied from 0.034 to 0.44 eV. Deposition was made with the beam incident at 0°, 30°, and 75° with respect to the surface normal. Ga was supplied from a simple evaporator and all growth was carried out under Ga-rich conditions. The thickness and morphology of the resulting films was characterized ex situ using RBS, Auger, TEM, and AFM. Of particular relevance to the growth of III-N compounds are the following results: (1) Selected energy epitaxial growth was observed, evidently via a direct reaction channel over a barrier of 0.3 ± 0.1 eV and mediated by the NH@sub 3@ translational energy. (2) A low energy reaction channel was also identified and ascribed to physisorption of the incoming NH@sub 3@ molecule followed by dissociative attachment of NH@sub x@ fragments. (3) Comparison of growth at 0° and 30° beam angles revealed total energy scaling, possibly due to rotational coupling of the above two reaction channels. (4) Deposition at grazing angle (75°) yielded faceting oriented towards the beam, indicating minimal mobility of the incident NH@sub 3@ and the attached NH@sub x@ fragments. The experimental evidence will be presented and the implications for III-N growth examined. Supported by ONR grant # N00014-95-1-0122