  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.
