Near-infrared photonic phase-change properties of transition metal ditellurides

We use the (Mo,W)Te₂ system to explore the potential of transition metal dichalcogenides (TMDs) as phase-change materials for integrated photonics. We measure the complex optical constant of MoTe₂ in both the 2H and 1T' phases by spectroscopic ellipsometry. We find that both phases have large refractive index, which is good for confined light-matter interaction volume. The change Δn between phases is of ℴ(1), which is large and comparable to established phase-change materials. However, both phases have large optical loss, which limits to figure of merit throughout the measured range. We further measure the NIR reflectivity of MoTe₂ and Mo_0.91W_0.09Te₂, in both the 2H and 1T' phases. The data show that the strong optical contrast between the 2H and 1T' structures persists even as the thermodynamic barrier between them is reduced by alloying. This bodes well for alloy design of phase-change materials.