Indirect to direct band gap crossover in two-dimensional WS2(1−x)Se2x alloys
Published in npj 2D Materials and Applications, 2021
In atomically thin transition metal dichalcogenide semiconductors, there is a crossover from indirect to direct band gap as the thickness drops to one monolayer, which comes with a fast increase of the photoluminescence signal. Here, we show that for different alloy compositions of WS2(1− x)Se2x this trend may be significantly affected by the alloy content and we demonstrate that the sample with the highest Se ratio presents a strongly reduced effect. The highest micro-PL intensity is found for bilayer WS2(1− x)Se2x(x=0.8) with a decrease of its maximum value by only a factor of 2 when passing from mono-layer to bi-layer. To better understand this factor and explore the layer-dependent band structure evolution of WS2(1− x)Se2x, we performed a nano-angle-resolved photoemission spectroscopy study coupled with first-principles calculations. We find that the high micro-PL value for bilayer WS2(1− x)Se2x(x=0.8) is due to the overlay of direct and indirect optical transitions. This peculiar high PL intensity in WS2(1− x)Se2x opens the way for spectrally tunable light-emitting devices.
Recommended citation: C. Ernandes, L. Khalil, H. Almabrouk, D. Pierucci, B. Zheng, J. Avila, P. Dudin, J. Chaste, F. Oehler, M. Pala, F. Bisti, T. Brulé, E. Lhuillier, A. Pan, A. Ouerghi, "Indirect to direct band gap crossover in two-dimensional WS2(1−x)Se2x alloys." npj 2D Materials and Applications 1, 7, (2021).
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