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Thickness Dependence of Electronic Properties of GaN Epi-layers

Published online by Cambridge University Press:  10 February 2011

W. Götz
Permanent address: Hewlett-Packard Company, 370 West Trimble Road, San Jose, CA 9513 1, USA
J. Walker
Xerox Palo Alto Research Center, Palo Alto, California 94304, USA
L.T. Romano
Xerox Palo Alto Research Center, Palo Alto, California 94304, USA
N.M. Johnson
Xerox Palo Alto Research Center, Palo Alto, California 94304, USA
R.J. Molnar
Massachusetts Institute of Technology, Lincoln Laboratory, 244 Wood Street, Lexington, Massachusetts 02173, USA
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The electronic properties of heteroepitaxial GaN were investigated for unintentionally doped, n-type films grown by hydride vapor phase epitaxy on sapphire substrates. The GaN layers were characterized by variable temperature Hall-effect measurement, capacitance-voltage (C-V) measurements, and deep level transient spectroscopy (DLTS). The measurements were performed on as-grown, 13 μn thick films and repeated after thinning by mechanical polishing to 7 μm and 1.2 μm. The room temperature electron concentrations as determined by the Hall-effect measurements were found to increase from ∼1017 cm−3 (13 μm) to ∼1020 cm−3 (1.2 μm) with decreasing film thickness. However, the C-V and DLTS measurements revealed that the ionized, effective donor and deep level concentrations, respectively, remained unchanged in regions close to the top surface of the films. These findings are consistent with the presence of a thin, highly conductive near interface layer which acts as a parasitic, parallel conduction path. Possible sources of such a shunt near the GaN/sapphire interface include oxygen contamination from the sapphire substrate or a structurally highly defective, 300 nm thick interface layer.

Research Article
Copyright © Materials Research Society 1997

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