Doping Dependence of the Thermal Conductivity of Hydride Vapor Phase Epitaxy Grown n -GaN/Sapphire (0001) Using a Scanni
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Doping Dependence Of The Thermal Conductivity Of Hydride Vapor Phase Epitaxy Grown n-GaN/Sapphire (0001) Using A Scanning Thermal Microscope D.I. FLORESCU*, V.A. ASNIN*, L.G. MOUROKH*, FRED H. POLLAK*, and R. J. MOLNAR** * Physics Department and New York State Center for Advanced Technology in Ultrafast Photonic Materials and Applications, Brooklyn College of CUNY, Brooklyn, NY 11210 ** Massachusetts Institute of Technology, Lincoln Laboratory, Lexington, MA 02420-9108 ABSTRACT We have measured the doping concentration dependence of the room temperature thermal conductivity (κ ) of two series of n-GaN/sapphire (0001) fabricated by hydride vapor phase epitaxy (HVPE). In both sets κ decreased linearly with log n, the variation being about a factor two decrease in κ for every decade increase in n. κ ≈ 1.95 W/cm-K was obtained for one of the most lightly doped samples (n = 6.9x1016 cm-3), higher than the previously reported κ ≈ 1.7-1.8 W/cm-K on lateral epitaxial overgrown material [V.A. Asnin et al, Appl. Phys. Lett. 75, 1240 (1999)] and κ ≈ 1.3 W/cm-K on a thick HVPE sample [E.K. Sichel and J.I. Pankove, J. Phys. Chem. Solids 38, 330 (1977)]. The decrease in the lattice component of κ due to increased phonon scattering from both the impurities and free electrons outweighs the increase in the electronic contribution to κ. INTRODUCTION Despite the considerable body of work, both experimental and theoretical, on the electronic, optical, and structural properties of group III nitrides [1] relatively little work has been reported on thermal conductivity κ . This quantity is of importance from both fundamental and applied perspectives. The lattice thermal conductivity is a function of the mean free path of the phonons and hence is determined by both intrinsic (phonon-phonon Umklapp scattering) and extrinsic (phonon-"defect", phonon-carrier scattering) factors [2]. Sichel and Pankove [3] determined κ of "bulk" hydride vapor phase epitaxy (HVPE) GaN as a function of temperature (25K
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