Phase-engineered SnSex toward SnSe2/SnSe heterostructure with improved thermal conductance by a low-temperature plasma-assisted chemical vapor reaction

In this work, the discovery of an abnormal p-type conductivity in SnSe2 thin films synthesized by a plasma-assisted chemical vapor reaction (PACVR) at a low temperature as low as 150 degrees C was reported. Due to a thermodynamically driven mechanism, three distinct phases including homogeneous SnSe2 and SnSe as well as a SnSe2/SnSe heterostructure were demonstrated. The SnSe2 homogeneous film was prepared by the PACVR from a thin Sn prelayer at a high substrate temperature on a glass substrate. The SnSe homogeneous film was prepared at a low temperature on a mica substrate regardless of the Sn prelayer thickness. Furthermore, the SnSe2/SnSe heterostructure film was prepared from a thick Sn prelayer on the glass substrate. All of the phases exhibit p-type conducting behavior because of hydrogen doping at the vapor-solid reaction interface during the PACVR. Furthermore, the first experimental evidence of intrinsic thermal conductivities of SnSe2 and SnSe thin film of 2.15 W/(m K) and 0.18 W/(m K), respectively, together with an interfacial thermal conductance of 11.32 MW m(-2) K-1 in between, was measured by Raman scattering behaviors. The low thermal conductivity make PACVR-synthesized SnSe2-based thin films feasible for thermoelectric applications. In particular, the SnSe2/SnSe heterostructure is the optimized phase for use in thermoelectric generators owing to not only its low thermal conductivity but also the strong accumulation of holes and phonons near the surface.