High Thermal Conductivity of Bulk GaN Single Crystal: An Accurate Experimental Determination
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High Thermal Conductivity of Bulk GaN Single Crystal: An Accurate Experimental Determination A. V. Inyushkin+1) , A. N. Taldenkov+, D. A. Chernodubov+ , V. V. Voronenkov∗, Yu. G. Shreter∗× 1) + National
Research Center Kurchatov Institute, 123182 Moscow, Russia ∗ Ioffe
× Peter
Institute, 194021 St. Petersburg, Russia
the Great St. Petersburg Polytechnic University, 195251 St. Petersburg, Russia Submitted 19 May 2020 Resubmitted 1 June 2020 Accepted 2 June 2020
Thermal conductivity κ(T ) of bulk single crystal GaN having wurtzite crystal structure has been measured in the direction parallel to the hexagonal plane at temperatures T between 5 and 410 K. The room temperature value of thermal conductivity is equal to 213±7 W m−1 K−1 . The κ(T ) reaches a peak of about 3770 W m−1 K−1 at T ≈ 28 K. The high value of κ(T ) at low temperatures indicates high quality of the sample under study. The lowest-temperature results can be very satisfactory explained by McCurdy, Maris, and Elbaum theory of phonon transport in the diffuse boundary scattering regime. Above the peak, the measured κ(T ) decreases steeply even at high temperatures. The discrepancies between our experimental results and recent first-principles calculations are discussed. DOI: 10.1134/S0021364020140039
I. Introduction. Gallium nitride and related compounds are attractive semiconductors for many electronic and optoelectronic devices due to their unique physical properties. Thermal conductivity is one of the basic properties from the design point of view because it determines in great extent the performance of high power devices. In pure and lightly doped GaN, the heat is transported by phonons. Charge carriers (electrons and holes) contribute very little to the total heat current at low and moderate temperatures as compared with the Debye temperature of about 650 K. A number of phonon scattering processes restrict the phonon thermal conductivity [1]. The phonon-phonon scattering processes due to lattice anharmonicity are considered as intrinsic processes and all others are extrinsic which can be controlled to some extent. Among anharmonic processes the most important are three-phonon one, both the normal N processes, which conserve the phonon momentum, and umklapp U processes, which do not conserve momentum. In some cases of relatively weak three-phonon processes, the next order four-phonon processes can play an essential role in thermal conductivity at high temperatures. The extrinsic processes include the phonon scattering from crystal lattice imperfections, such as point defects (foreign atoms, vacancies, impurity isotopes), extended defects (dislocations, atomic clus1) e-mail:
ters, stacking faults, internal and external boundaries), as well as from the free and bound charge carriers in doped semiconductors. In thermal conductivity of crystals with low defect concentration, different scattering processes dominate in fairly well-isolated temperature intervals. At low enough temperatures the phonon scattering from crystal boundaries governs the thermal con
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