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

Paper SE-ThA6
In-Situ Surface Cleaning of GaN Using Hyperthermal Molecular Beams

Thursday, November 5, 1998, 3:40 pm, Room 327

Session: Seeded Supersonic Beam Epitaxial Growth
Presenter: A. Michel, North Carolina State University
Authors: A. Michel, North Carolina State University
E. Chen, North Carolina State University
O. Nam, North Carolina State University
D. Thomson, North Carolina State University
R.F. Davis, North Carolina State University
H.H. Lamb, North Carolina State University
Correspondent: Click to Email
Selected energy epitaxy (SEE) of GaN on MOVPE-grown GaN/6H-SiC substrates requires in-situ surface cleaning techniques that are effective at removing carbon and oxygen contamination without roughening or otherwise damaging the surface. Remote hydrogen plasma cleaning has been used to remove contaminants from GaN substrates prior to RF plasma-assisted MBE growth; however, the effects of hydrogen plasma exposure on surface roughness and substrate electrical properties have not been reported.@footnote 1@ Nitrogen plasma exposure can destroy surface steps on GaN/6H-SiC substrates, as evidenced by in-situ low energy electron microscopy (LEEM).@footnote 2@ Energetic beams of neutral atoms and molecules provide an alternative to plasma sources for in-situ cleaning and subsequent growth. Hyperthermal molecular beams are generated by seeding heavy species (e.g., NH@sub 3@, Kr) in a supersonic expansion of a lighter gas (e.g., He, H@sub 2@). In this work, in-situ cleaning of MOVPE-grown GaN/AlN/6H-SiC substrates using hyperthermal molecular beams was investigated. Removal of surface carbon and oxygen contaminants was achieved by heating at 730°C under a hyperthermal NH@sub 3@ beam. Oxygen is removed primarily by thermal desorption; however, carbon removal occurs only under an NH@sub 3@ flux. We infer that adsorbed H atoms produced by NH@sub 3@ decomposition react with carbonaceous species on the GaN surface to produce volatile hydrocarbons. Ex-situ atomic force microscopy (AFM) indicates that atomically smooth surfaces with regular steps are produced by NH@sub 3@ beam cleaning. In on-going work, we are investigating the use of dual hyperthermal Kr and NH@sub 3@ beams for GaN cleaning. The effects of kinetic energy on surface contamination removal and surface morphology will be discussed. @FootnoteText@ @footnote 1@W.C. Hughes, W.H. Rowland, Jr., M.A.L. Johnson, S. Fujita, J.W. Cook, Jr., J. Ren, and J.A. Edmond, J. Vac. Sci. Tech. A, 13, 1571 (1995).@footnote 2@E. Bauer, private communication.