  Transition metal dichalcogenide (TMD) alloys have attracted great interests
in recent years due to their tunable electronic properties, especially the
semiconductor-metal phase transition, along with their potential applications
in solid-state memories and thermoelectrics. However, the thermal conductivity
of layered two-dimensional (2D) TMD alloys remains largely unexplored despite
that it plays a critical role in the reliability and functionality of
TMD-enabled devices. In this work, we study the temperature-dependent
anisotropic thermal conductivity of the phase-transition 2D TMD alloys
WSe2(1-x)Te2x in both the in-plane direction (parallel to the basal planes) and
the cross-plane direction (along the c-axis) using time-domain
thermoreflectance measurements. In the WSe2(1-x)Te2x alloys, the cross-plane
thermal conductivity is observed to be dependent on the heating frequency
(modulation frequency of the pump laser) due to the non-equilibrium transport
between different phonon modes. Using a two-channel heat conduction model, we
extracted the anisotropic thermal conductivity at the equilibrium limit. A
clear discontinuity in both the cross-plane and the in-plane thermal
conductivity is observed as x increases from 0.4 to 0.6 due to the phase
transition from the 2H to Td phase in the layered 2D alloys. The temperature
dependence of thermal conductivity for the TMD alloys was found to become
weaker compared with the pristine 2H WSe2 and Td WTe2 due to the atomic
disorder. This work serves as an important starting point for exploring phonon
transport in layered 2D alloys.
