Method for High Accuracy Measurements of Thermal Conductivity in c-BAs Crystals

Student’s name: William Ward Home Institution: University of Wisconsin–Madison NNCI Site: MRC @ UT Austin REU Principal Investigator: Dr. Li Shi – Department of Mechanical Engineering, UT Austin REU Mentor: Woongchul Choi – Department of Mechanical Engineering, UT Austin Abstract: Semiconducting materials with ultrahigh thermal conductivities and thermopower have the potential to enhance the performance of microelectronic and thermoelectric power devices. One material of interest is cubic BAs (c-BAs), which is a III-V semiconductor with an ultrahigh thermal conductivity, high Seebeck coefficient, high hole mobility, and advantageous mechanical properties for microelectronic applications. First principles calculations show that c-BAs has a room temperature thermal conductivity of 2000 W/(m*K) , but empirical measurements haven’t been able to verify this due to high thermal contact resistance. There is also a lack of published data on the Seebeck coefficient of c-BAs, which is necessary to understand its physical relationship with phonon phenomena. A novel thin film thermometry and cryostat device was used to obtain cryogenic thermal conductivity measurements of CVT-grown c-BAs crystals with high accuracy. A conventional solid-state thermoelectric measuring device was used to validate the temperature-dependent thermopower in these crystals. We expect that these techniques will achieve the peak thermal conductivity and Seebeck coefficient in c-BAs crystals to provide evidence of its importance in microelectronic applications. Future work in this area will be applying these measurement techniques to other semiconducting crystals with ultrahigh thermal conductivities like TaN.