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

Invited Paper SE-ThM5
Wurtzite GaN Surface Structure Studied by Scanning Tunneling Microscopy and Total Energy Calculations

Thursday, November 5, 1998, 9:40 am, Room 327

Session: In Situ Characterization and Real-Time Diagnostics of Surface Growth Processes
Presenter: A.R. Smith, Carnegie Mellon University
Authors: A.R. Smith, Carnegie Mellon University
R.M. Feenstra, Carnegie Mellon University
D.W. Greve, Carnegie Mellon University
M.-S. Shin, Carnegie Mellon University
M. Skowronski, Carnegie Mellon University
J. Neugebauer, Fritz-Haber-Institut der MPG, Germany
J.E. Northrup, Xerox Palo Alto Research Center
Correspondent: Click to Email
Using scanning tunneling microscopy (STM) and electron diffraction, two new families of reconstructions have been identified on wurtzite GaN surfaces. First-principles theoretical calculations have yielded a number of novel structural models - many consisting of metallic Ga surface layers - for these reconstructions. The two families of reconstructions are those associated with the inequivalent (0001) and (000-1) surfaces, denoted as Ga-face and N-face respectively. Films are grown using molecular beam epitaxy with an RF plasma source to activate the N@sub 2@ molecules. The N-face results from nucleating the growth directly on sapphire, while the Ga face is prepared through homoepitaxial growth on an MOCVD-grown GaN/sapphire template. For either polarity, smooth growth occurs under Ga-rich growth conditions whereas N-rich growth leads to surface roughening. On the N-face, the least Ga-rich structure is the 1x1, composed of a single Ga monolayer (or adlayer) bonded to the ideal, N-terminated bilayer. Higher-order reconstructions on this face, 3x3, 6x6, and c(6x12), occur with increasing Ga coverage. On the Ga-face, the most Ga-rich structure is the pseudo-1x1, consisting of a double layer of Ga atoms in a fluid-like discommensurate structure on the surface. Removal of Ga atoms from the pseudo-1x1 results in the 6x4, 5x5, and 2x2, in order of decreasing Ga coverage. The 6x4 and 5x5 appear to be composed primarily of Ga adatoms. The 2x2, on the other hand, is formed through nitridation of the annealed surface or by growth under nearly N-rich conditions and therefore is consistent with a N adatom 2x2. @FootnoteText@ This work is supported by the Office of Naval Research under contract N00014-96-1-0214.