Electrical and thermal transport properties of S- and Te-doped InSe alloys

Metal chalcogenide materials, including indium selenide (InSe), have attracted attention as potential thermoelectric materials due to their intrinsically low thermal conductivity, which is due to their layered structure with weak atomic bonding. However, their low electrical conductivity should be increased for application as thermoelectric materials. In this study, we examined the electrical and thermal transport properties of 7% S- or Te-doped InSe polycrystalline alloys (InSe_0.93S_0.07 and InSe_0.93Te_0.07). These anion substitutions increased the electrical conductivity of InSe, while the enhancement was larger for the Te-doped InSe with a smaller bandgap. The negative Seebeck coefficient did not change significantly upon doping, resulting in enhancement of the power factor. Doping caused a relatively large reduction of thermal conductivity due to additional point defect phonon scattering. Consequently, the thermoelectric figure of merit (zT) increased by 62% and 230% to a maximum of 0.13 and 0.28 at 735 K for InSe_0.93S_0.07 and InSe_0.93Te_0.07, respectively, which offers the possibility of InSe-based thermoelectric materials. Cation doping could increase the zT of S/Te-doped InSe further.