Thermal conductivity of GaN crystals in 4.2 – 300 K range A. Jez ˙owski a , B.A. Danilchenko b , M. Boc ´kowski c , I. Grzegory c , S. Krukowski c , T. Suski c , T. Paszkiewicz d, * a Institute of Low Temperature Physics, Polish Academy of Sciences, Wroclaw, Poland b Institute of Physics, National Academy of Sciences of Ukraine, Prospect Nauki 46, 252650 Kiev, Ukraine c High Pressure Research Center, Polish Academy of Sciences, Warsaw, Poland d Institute of Physics, University of Rzeszo ´w, ul. Rejtana 16A, PL-35-310 Rzeszo ´w, Poland Received 7 July 2003; accepted 15 July 2003 by M. Grynberg Abstract Results of measurements of thermal conductivity of bulk GaN crystals in the temperature interval 4.2 – 300 K are reported. Experiments were performed on two types of single GaN crystals grown under high-pressure: highly conducting n-type sample and on a highly resistive sample compensated by magnesium doping. For n-GaN crystals, the highest thermal conductivity k max is equal to 1600 W/m K at T max ¼ 45 K; and k . 220 W/m K at 300 K. Our analysis indicates that for the best n-GaN crystal and for T $ T max ; the contribution of Umklapp phonon scattering processes dominate whereas for other samples scattering of phonons by point mass defects represents the main contribution. The dependence of kðT Þ is used to reveal possible mechanisms of thermal resistance of GaN crystals at temperatures T max : Our thermal conductivity measurements yields Debye’s temperature u D < 400 K: q 2003 Elsevier Ltd. All rights reserved. PACS: 44.10. þ a Keywords: A. Gallium nitride; D. Heat conduction 1. Introduction Since in our measurements we deal with semiconducting crystals of GaN, both phonons and electrons carry energy. However, due to small concentration of electrons only contribution of phonons to heat transport can be considered. Various scattering mechanisms remove phonons from heat fluxes, thus creating thermal resistance [1]. Among various scattering mechanisms, e.g. phonon Umklapp processes or scattering of phonons by boundaries, thermal resistance related to structural defects is of particular interest. The understanding of contribution of these kinds of scattering processes allows one to extract useful information about their presence and concentration. On the other hand, it is a well-known fact that efficient heat removal is critical to the performance of high power semiconductor electronic devices and lasers. In particular, high-pressure grown GaN [2] has been used as a substrate for high quality epitaxial layers, heterostructures, and blue laser diode [3]. For this reason, thermal conductivity and heat capacity are interesting characteristics of GaN. The early measurements of thermal conductivity of GaN (400 mm of material fabricated by HVPE) were performed by Sichel et al. [4] for 25 K , T , 360 K: The small value of k ¼ 130 W/m K ðT ¼ 300 KÞ was attributed by the authors to high impurity concentration (at least 10 18 cm 23 ) and to the presence of small angle grain boundaries. Measurements of k reported in the literature were performed at room temperature mainly. Scanning thermal microscopy was used to measure thermal conduc- tivity of 170 and 150 W/m K, respectively, for the laterally overgrown films of GaN on SiC and the GaN deposition in 0038-1098/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0038-1098(03)00629-X Solid State Communications 128 (2003) 69–73 www.elsevier.com/locate/ssc * Corresponding author. Tel.: þ48-17-852-94-18; fax: þ 48-17- 852-67-92. E-mail address: tapasz@univ.rzeszow.pl (T. Paszkiewicz).