Thermal Light Emission from Monolayer MoS2.

Layered transition metal dichalcogenide semiconductors, such as MoS2 and WSe2 , exhibit a range of fascinating properties and are being currently explored for a variety of electronic and optoelectronic devices. These properties include a low thermal conductivity and a large Seebeck coefficient, which make them promising for thermoelectric applications. Moreover, transition metal dichalcogenides undergo an indirect-to-direct bandgap transition when thinned down in thickness, leading to strong excitonic photo- and electroluminescence in monolayers. Here, it is demonstrated that a MoS2 monolayer sheet, freely suspended in vacuum over a distance of 150 nm, emits visible light as a result of Joule heating. Due to the poor transfer of heat to the contact electrodes, as well as the suppressed heat dissipation through the underlying substrate, the electron temperature can reach ≈1500-1600 K. The resulting narrow-band light emission from thermally populated exciton states is spatially located to an only ≈50 nm wide region in the center of the device and goes along with a negative differential electrical conductance of the channel.

Controlled Generation of a p-n Junction in a Waveguide Integrated Graphene Photodetector.

With its electrically tunable light absorption and ultrafast photoresponse, graphene is a promising candidate for high-speed chip-integrated photonics. The generation mechanisms of photosignals in graphene photodetectors have been studied extensively in the past years. However, the knowledge about efficient light conversion at graphene p-n junctions has not yet been translated into high-performance devices. Here, we present a graphene photodetector integrated on a silicon slot-waveguide, acting as a dual gate to create a p-n junction in the optical absorption region of the device. While at zero bias the photothermoelectric effect is the dominant conversion process, an additional photoconductive contribution is identified in a biased configuration. Extrinsic responsivities of 35 mA/W, or 3.5 V/W, at zero bias and 76 mA/W at 300 mV bias voltage are achieved. The device exhibits a 3 dB bandwidth of 65 GHz, which is the highest value reported for a graphene-based photodetector.