LCC researcher, Associate Professor Shenghong Ju's research group recently published a paper on “High thermoelectric performance in metastable phase of silicon: a first−principles study” in Applied Physics Letters.
In this work, both thermal and electrical transport properties of diamond-cubic Si (Si-I) and metastable R8 phases of Si (Si-XII) are comparatively studied by using first-principles calculations combined with the Boltzmann transport theory. The metastable Si-XII shows one magnitude lower lattice thermal conductivity than stable Si-I from 300 to 500 K, attributed from the stronger phonon scattering in three-phonon scattering processes of Si-XII. For electronic transport properties, although Si-XII with smaller bandgap (0.22 eV) shows a lower Seebeck coefficient, the electrical conductivities of anisotropic n-type Si-XII show considerable values along the x axis due to the small effective masses of electrons along this direction. The peaks of the thermoelectric figure of merit (ZT) in n-type Si-XII are higher than that of p-type ones along the same direction. Owing to the lower lattice thermal conductivity and optimistic electrical conductivity, Si-XII exhibits larger optimal ZT compared with Si-I in both p- and n-type doping. For n-type Si-XII, the optimal ZT values at 300, 400, and 500 K can reach 0.24, 0.43, and 0.63 along the x axis at carrier concentrations of 2.6×1019,4.1×1019, and 4.8×1019 cm−3, respectively. The reported results elucidate that the metastable Si could be integrated to the thermoelectric power generator.
Yongchao Rao, Doctoral Student of LCC
Dr. Shenghong Ju, Associate Professor and Assistant Dean of LCC