Energy Scaling of Compositional Disorder in Ternary Transition-Metal Dichalcogenide Monolayers

Alloying semiconductors are often used to tune the material properties desired for device applications. The price for this tunability is the extra disorder caused by alloying. In order to reveal the features of the disorder potential in alloys of atomically thin transition-metal dichalcogenides (TMDs) such as MoxW1-xSe2, the exciton photoluminescence is measured in a broad temperature range between 10 and 200 K. In contrast to the binary materials MoSe2 and WSe2, the ternary system demonstrates non-monotonous temperature dependences of the luminescence Stokes shift and of the luminescence linewidth. Such behavior is a strong indication of a disorder potential that creates localized states for excitons and affects the exciton dynamics responsible for the observed non-monotonous temperature dependences. A comparison between the experimental data and the results obtained by Monte Carlo computer simulations provides information on the energy scale of the disorder potential and also on the shape of the density of localized states created by disorder. Statistical spatial fluctuations in the distribution of the chemically different material constituents are revealed to cause the disorder potential responsible for the observed effects. A deeper understanding of the disorder-induced effects is vital for prospective TMD alloy-based devices.