Measurements of the energy band gap and valence band structure ofAgSbTe2

The de Haas-van Alphen effect, galvanomagnetic and thermomagnetic properties of high-quality crystals of ${\text{AgSbTe}}_{2}$ are measured and analyzed. The transport properties reveal the material studied here to be a very narrow-gap semiconductor $({E}_{g}\ensuremath{\approx}7.6\ifmmode\pm\else\textpm\fi{}3\text{ }\text{meV})$ with $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }{\text{cm}}^{\ensuremath{-}3}$ holes in a valence band with a high density of states and thermally excited $\ensuremath{\sim}{10}^{17}\text{ }{\text{cm}}^{\ensuremath{-}3}$ high-mobility $(2200\text{ }{\text{cm}}^{2}/\text{Vs})$ electrons at 300 K. The quantum oscillations are measured with the magnetic field oriented along the $⟨111⟩$ axis. Taken together with the Fermi energy derived from the transport properties, the oscillations confirm the calculated valence band structure composed of 12 half-pockets located at the $X$-points of the Brillouin zone, six with a density-of-states effective mass ${m}_{da}^{\ensuremath{\ast}}⪢0.21{m}_{e}$ and six with ${m}_{db}^{\ensuremath{\ast}}⪢0.55{m}_{e}$, giving a total density-of-states effective mass, including Fermi pocket degeneracy, of ${m}_{d}^{\ensuremath{\ast}}\ensuremath{\approx}1.7\ifmmode\pm\else\textpm\fi{}0.2{m}_{e}$ (${m}_{e}$ is the free electron mass). The lattice term dominates the thermal conductivity, and the electronic contribution in samples with both electrons and holes present is in turn dominated by the ambipolar term. The low thermal conductivity and very large hole mass of ${\text{AgSbTe}}_{2}$ make it a most promising $p$-type thermoelectric material.