Measurements of heat capacity and thermal conductivity of β-Ga2O3 and β-(AlxGa1–x)2O3 bulk crystals grown by the Czochralski method

One of the application fields of bulk gallium oxide crystals is the manufacture of substrates for epitaxial growth of device structures for power electronics and optoelectronics in the Ga2O3/(AlxGa1–x)2O3 system. For most instrument designs, the substrate serves as a channel for heat removal from the device to an external heat sink. This property stresses the importance of information about the thermal characteristics of bulk crystals of gallium oxide and a solid solution of gallium and aluminum oxide, particularly about the heat capacity and thermal conductivity. In this work, we measured the heat capacity of bulk crystals of the β-modification of pure gallium oxide (β-Ga2O3) obtained by the Czochralski method, as well as of a double solid solution of gallium and alumina oxide β-(AlxGa1–x)2O3 in the range of temperatures from 25 °C to 480 °C and for various values of the Al concentration. Samples of bulk crystals were grown in an industrial installation “Nika-3” by pulling from the melt (Czochralski method). Further, the specific heat was measured on samples specially prepared from bulk crystals by differential scanning calorimetry. The thermal conductivity in the [010] crystallographic direction was measured by the method using a flat heat source (hot disk method). The dependence of the specific heat capacity of β-(AlxGa1–x)2O3 crystals on Al concentration was obtained for the atomic concentration of aluminum ranging from 0 (pure gallium oxide) to 9.11 at.%. The influence of the Al content on the heat capacity of the material is analyzed. The temperature dependence of the thermal conductivity of β-Ga2O3 in the [010] direction (direction of growth) in the temperature range from 43 °С to 120 °С was also obtained. The results of the study can be used to investigate the thermal properties of gallium oxide, as well as to solve the problem of heat removal for electronic devices based on gallium oxide.