  Alloyed transition metal dichalcogenides provide an opportunity for coupling
band engineering with valleytronic phenomena in an atomically-thin platform.
However, valley properties in alloys remain largely unexplored. We investigate
the valley degree of freedom in monolayer alloys of the phase change candidate
material WSe$_{2(1-x)}$Te$_{2x}$. Low temperature Raman measurements track the
alloy-induced transition from the semiconducting 1H phase of WSe$_2$ to the
semimetallic 1T$_d$ phase of WTe$_2$. We correlate these observations with
density functional theory calculations and identify new Raman modes from W-Te
vibrations in the 1H alloy phase. Photoluminescence measurements show ultra-low
energy emission features that highlight alloy disorder arising from the large
W-Te bond lengths. Interestingly, valley polarization and coherence in alloys
survive at high Te compositions and are more robust against temperature than in
WSe$_2$. These findings illustrate the persistence of valley properties in
alloys with highly dissimilar parent compounds and suggest band engineering can
be utilized for valleytronic devices.
