Monolayers of molybdenum and tungsten dichalcogenides are direct bandgap semiconductors, which makes them promising for opto-electronic applications. In particular, van der Waals heterostructures consisting of monolayers of MoS2 sandwiched between atomically thin hexagonal boron nitride (hBN) and graphene electrodes allows one to obtain light emitting quantum wells (LEQWs) with low-temperature external quantum efficiency (EQE) of 1%. However, the EQE of MoS2 and MoSe2-based LEQWs shows behavior common for many other materials: it decreases fast from cryogenic conditions to room temperature, undermining their practical applications. Here we compare MoSe2 and WSe2 LEQWs. We show that the EQE of WSe2 devices grows with temperature, with room temperature EQE reaching 5%, which is 250x more than the previous best performance of MoS2 and MoSe2 quantum wells in ambient conditions. We attribute such a different temperature dependences to the inverted sign of spin-orbit splitting of conduction band states in tungsten and molybdenum dichalcogenides, which makes the lowest-energy exciton in WSe2 dark.
@article{arxiv.1511.06265,
title = {WSe2 light-emitting tunneling transistors with enhanced brightness at room temperature},
author = {F. Withers and O. Del Pozo-Zamudio and S. Schwarz and S. Dufferwiel and P. M. Walker and T. Godde and A. P. Rooney and A. Gholinia and C. R. Woods and P. Blake and S. J. Haigh and K. Watanabe and T. Taniguchi and I. L. Aleiner and A. K. Geim and V. I. Falko and A. I. Tartakovskii and K. S. Novoselov},
journal= {arXiv preprint arXiv:1511.06265},
year = {2015}
}