Thermoelectric Properties of GaN with Carrier Concentration Modulation: An Experimental and Theoretical Investigation.

The present work investigates the less explored thermoelectric properties of n-type GaN semiconductors by combined both the experimental and computational tools. Seebeck coefficients of epitaxial thin films of GaN were experimentally measured in the wide temperature range from 77 K to 650 K in steps of ~10 K covering both low and high-temperature regimes as a function of carrier concentration 2 x1016, 2 x 1017, 4 x 1017 and 8 x 1017 cm-3. The measured Seebeck coefficient at room temperature was found to be highest, -374 microV/K, at the lowest concentration of 4 x 1016 cm-3 and decreases in magnitude monotonically (-327.6 microV/K, -295 microV/K, -246 microV/K for 2 x 1017, 4 x 1017, 8 x 1017 cm-3, respectively) as the carrier concentration of samples increases. Seebeck coefficient remains negative in the entire temperature range under study indicate that electrons are dominant carriers. To understand the temperature-dependent behavior, we have also carried out the electronic structure, and transport coefficients calculations by using Tran-Blaha modified Becke-Johnson (TB-mBJ) potential, and semiclassical Boltzmann transport theory implemented in WIEN2k and BoltzTraP code, respectively. The experimentally observed carrier concentrations were used in the calculations. The estimated results obtained under constant relaxation time approximations provide a very good agreement between theoretical and experimental data of Seebeck coefficients in the temperature range of 260 to 625 K.