Layered 2D MoSe2(1–x)Te2x Alloys: Promising Thermoelectric Material with Tunable Thermal and Electrical Transport

Transition metal dichalcogenide alloys have received enormous attention since the alloying of different elements allows optimization of thermal and electrical transport properties. In the present study, the thermal transport properties of 2H phase of a single- to few-layer MoSe2(1–x)Te2x alloys (x = 0.0, 0.25, 0.5, 0.75, and 1) are investigated using optothermal Raman spectroscopy. The synthesis of 2H MoSe2(1–x)Te2x crystals is achieved using a chemical vapor transport technique, and the resulting highly oriented crystals are characterized using various physicochemical techniques. Subsequently, the temperature- and power-dependent Raman scattering behavior of alloys in monolayer to few layers is investigated. It is found that with increasing temperature and power, A1g and E2g modes of all compositions show a red shift. The first-order temperature and power coefficients are determined and found to be composition-tunable. Subsequently, the thermal conductivity values for monolayer alloys are estimated and found to be lower for alloys than those of the pristine counterparts due to enhanced phonon scattering in mixed alloys. The lowest thermal conductivity of 4.23 ± 0.69 W m–1·K–1 is obtained for the composition MoSe1.0Te1.0. Further, the electrical transport behavior of the alloys as a function of composition and thickness reveals perfect ambipolarity for an equal fraction of Se and Te showing high electron and hole mobilities with an Ion/Ioff ratio of ∼106. The excellent electrical properties and low thermal conductivities observed for the MoSe1.0Te1.0 alloy may give rise to a good thermoelectric material.