We use the (Mo,W)Te_2 system to explore the potential of transition metal dichalcogenides (TMDs) as phasechangematerials for integrated photonics. We measure the complex optical constant of MoTe_2 in both the 2H and1T’ phases by spectroscopic ellipsometry. We find that both phases have large refractive index, which is good forconfined light-matter interaction volume. The change Δ_ between phases is of ?(1) , which is large andcomparable to established phase-change materials. However, both phases have large optical loss, which limits tofigure of merit throughout the measured range. We further measure the NIR reflectivity of MoTe_2 andMo_(0.91)W_(0.09)Te_2, in both the 2H and 1T’ phases. The data show that the strong optical contrast between the 2H and1T’ structures persists even as the thermodynamic barrier between them is reduced by alloying. This bodes wellfor alloy design of phase-change materials.
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