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Proceedings Paper

Surface spatial profiles of defects in GaN
Author(s): D. K. Johnstone; S. Akarca-Biyikli; J. Xie; Y. Fu; C. W. Litton; H. Morkoc
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Paper Abstract

Surface profiles of deep levels in GaN sample grown by metal-organic chemical vapor deposition and by hydride vapor phase epitaxy are measured by differential deep level transient spectroscopy (DDLTS). The concentration of acceptor defects at the surface are expected to be lower than the bulk defect concentration because of the shift in Fermi level at the surface, based on theoretical estimates of defect formation energies and the band bending at the surface from spontaneous polarization. Similarly, donor defects are expected to increase in concentration as the surface is approached. The measured concentration profiles of various traps are found to span the range of behavior, from constant, to increasing or decreasing at the interface. Deep level profiling is therefore seen as an important tool to assist in determining defect composition. Although the behavior is as expected, the change in concentration from bulk to surface, is larger than measured values for the defects with the lowest formation energies, based on a conservative estimate of band bending. The difference may reflect a band bending that is different at the growth temperature than predicted, or a consequence of non-equilibrium growth conditions. As growth proceeds, the defects incorporated at the surface are in a non-equilibrium concentration when covered by subsequent layers, unless there is a mechanism whereby equilibrium defects can be formed, e.g. VGa by forming interstitial Ga, or there is enough energy for defect diffusion to take place. Peaks in the defect profile were measured, as would be expected for a donor defect formed at the surface, but with a non-equilibrium concentration in the bulk, driving diffusion toward the surface.

Paper Details

Date Published: 11 February 2006
PDF: 9 pages
Proc. SPIE 6121, Gallium Nitride Materials and Devices, 61210N (11 February 2006); doi: 10.1117/12.653320
Show Author Affiliations
D. K. Johnstone, SEMETROL (United States)
S. Akarca-Biyikli, Virginia Commonwealth Univ. (United States)
J. Xie, Virginia Commonwealth Univ. (United States)
Y. Fu, Virginia Commonwealth Univ. (United States)
C. W. Litton, Air Force Research Lab. (United States)
H. Morkoc, Virginia Commonwealth Univ. (United States)

Published in SPIE Proceedings Vol. 6121:
Gallium Nitride Materials and Devices
Cole W. Litton; James G. Grote; Hadis Morkoc; Anupam Madhukar, Editor(s)

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