High electron mobility in free-standing GaN substrates
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High electron mobility in free-standing GaN substrates A. Saxler,a) D. C. Look,b) S. Elhamri,c) J. Sizelove, D. Cull, and W. C. Mitchel Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Ohio M. Callahan, D. Bliss, L. Bouthillette, Sheng-Qi Wang Air Force Research Laboratory, Sensors Directorate, Hanscom AFB, MA C. M. Sung Center for Advanced Materials, University of Massachusetts, Lowell, MA S. S. Park and K. Y. Lee Samsung Advanced Institute of Technology, P.O. Box 111, Suwon, Korea. ABSTRACT High peak electron mobilities were observed in free-standing c-plane GaN substrates. Two layers, a low mobility degenerate layer and a high mobility bulk layer, were present in these samples. The carrier concentrations and mobilities for the layers were extracted using two methods: 1) magnetic field dependent Hall effect analysis and 2) a simple two carrier model with the assumption that one of the layers is degenerate. In addition, measurements were performed after etching away the degenerate layer. The mobility of the bulk layer is found to peak at nearly 8000 cm2/Vs at 60K using the magnetic field dependent Hall effect data. Record room temperature mobility for bulk GaN of 1190 cm2/V s was measured. INTRODUCTION Many applications exist for the III-Nitrides in high-power and high-temperature electronics,1 solar-blind ultraviolet photodetectors,2 and blue and ultraviolet light emitting and laser diodes.3 However, materials issues still dominate. One of the remaining issues is the lack of availability of high quality GaN substrates. GaN substrates with low dislocation densities and low concentrations of point defects such as impurities and vacancies can be expected to have much higher mobilities than those which have been observed in highly defective thin films or bulk materials which typically have high impurity concentrations. In this paper, the electrical properties of a new type of GaN substrate have been studied. Different methods will be compared for separating the electrical properties of the different layers in these freestanding hydride vapor phase epitaxy (HVPE) grown substrates. The details of the substrate growth will be reported elsewhere.4
a) b) c)
Electronic mail: [email protected] Also at: Semiconductor Research Center, Wright State University, Dayton, OH 45435. Permanent address: University of Dayton, Dept. of Physics, Dayton, OH 45469. G7.2.1
RESULTS AND DISCUSSION
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As seen in Figure 1, x-ray diffraction was used to determine that the radius of curvature for crystal lattice planes was 0.6m. This strong curvature is reflected in the broadening of the x-ray rocking curves. The back of the wafer showed additional signs of mosaic broadening, while the front surface showed only the curvature broadening. Details of these measurements will be reported elsewhere.
GaN (0006) front concave 0.645 +/- 0.004 m -4
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