The thermoelectric figure of merit is measured and theoretically analyzed for $n$-type Si-doped InGaAlAs III-V quaternary alloys at high temperatures. The Seebeck coefficient, electrical conductivity, and thermal conductivity of a Si-doped ${\left({\text{In}}_{0.53}{\text{Ga}}_{0.47}\text{As}\right)}_{0.8}{\left({\text{In}}_{0.52}{\text{Al}}_{0.48}\text{As}\right)}_{0.2}$ of $2\mu \text{m}$ thickness lattice matched to InP substrate grown by molecular-beam epitaxy are measured up to 800 K. The measurement results are analyzed using the Boltzmann transport theory based on the relaxation-time approximation and the theoretical calculation is extended to find optimal carrier densities that maximize the figure of merit at various temperatures. The figure of merit of 0.9 at 800 K is measured at a doping level of $1.9\times {10}^{18}{\text{cm}}^{-3}$ and the theoretical prediction shows that the figure of merit can reach 1.3 at 1000 K at a doping level of $1.5\times {10}^{18}{\text{cm}}^{-3}$.

• Received 9 February 2010

DOI:https://doi.org/10.1103/PhysRevB.81.235209