Adv. Mater. 29, 1701304 (2017)

Monolayer transition-metal dichalcogenites (TMDs) are direct-bandgap semiconductors characterized by strong light–matter interaction, the sought-after property in optoelectronics and photonics. Besides, low thermal conductivity and large thermopower of TMDs endows them with potential for applications in thermoelectrics. Now, L. Dobusch et al. exploit these properties and show thermal–visible light emission from a monolayer MoS2 that occurs as the result of Joule power dissipation.

A MoS2 flake, serving as a field-effect transistor channel, is suspended over a pre-patterned 150-nm-wide trench. Light emission localized to the suspended region sets in when the transistor is reverse biased with the gate voltage above the threshold. Electrons in the TMD monolayer can reach extremely high temperatures due to intrinsically inefficient heat transfer and poor vertical heat dissipation in the substrate-free region. Thus, hot carriers can quickly populate excitonic states and radiatively recombine in the centre of the device. The onset of the light emission is in the negative differential conductance regime. Its intensity increases at larger negative voltages until the device finally breaks down. From a practical point of view, the results suggest that thermal management may be needed to ensure reliability and stable performance of TMD electronics.