AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1+EM-TuM

Paper SS1+EM-TuM7
Deep Level Electronic States of Clean GaN (0001)(1x1) Surfaces Prepared by In Decapping

Tuesday, October 26, 1999, 10:20 am, Room 606

Session: Nitrides and Compound Semiconductors
Presenter: A.P. Young, Ohio State University
Authors: A.P. Young, Ohio State University
L. Brillson, Ohio State University
C. Tu, University of California, San Diego
Correspondent: Click to Email
The tremendous interest in the properties of GaN surfaces and interfaces has created a need for new techniques for preparing clean, ordered surfaces under ultrahigh vacuum (UHV) conditions. Furthermore, the electronic properties associated with different interface preparations are not well understood at present. In contrast to surfaces prepared by N+ bombardment or Ga overcoat annealing cycles at 900C, clean and ordered GaN (0001) (1x1) surfaces can be produced directly from MBE-grown surfaces after removal of an In cap layer at 650C. These surfaces are comparable to those clean, ordered surfaces reported elsewhere. We have used electron-excited nanometer luminescence spectroscopy (EENLS) to measure these states in the band gap of MBE-GaN deposited on a GaN/sapphire composite substrate. The GaN was cleaned in UHV via thermal desorption of a thin (~50 ML) metallic In layer deposited prior to removal of the specimen from the growth chamber. This relatively low temperature desorption presents a benign method of transporting and processing GaN for device applications. Auger Electron Spectroscopy (AES) results show that if the In can uniformly cover the surface, it can prevent contamination during atmospheric exposure without reacting or diffusing into the GaN layer. The as-prepared surface morphology, measured via ex situ atomic force microscopy (AFM), indicated significant islanding of the In on the surface with approximate lateral size of 250 nm and height of 30 nm. Furthermore, a Ga signal, probably in the form of an oxide, was observed via AES indicating that some of the surface was not covered by In. The In was selectively desorbed from the GaN without reacting to produce InGaN. 8 ML of Ga were then deposited and the surface flashed once to 690C to reduce residual O and C contamination yielding a sharp (1x1) low energy electron diffraction (LEED) pattern. EENLS at a probe energy of 350 V (probe depth » 3 nm) indicated substantial "yellow" (YL) emission within the bandgap centered at 2.22 eV (FWHM = 0.4 eV) with only minimal near band edge (NBE) emission. YL emission remains constant while NBE increases with depth of excitation, indicating only states intrinsic to the GaN bulk. Subsequent AFM reveals Ga droplets residual to the flash annealing. Thus, In decapping introduces no new states at the clean, ordered GaN surface.