Kevin Han

Large-area and bright pulsed electroluminescence in monolayer semiconductors

Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electroluminescent device based on transition-metal dichalcogenide monolayers (MoS2, WS2, MoSe2, and WSe2) to overcome these problems. Electroluminescence from this dopant-free two-terminal device is obtained by applying an AC voltage between the gate and the semiconductor. Notably, the electroluminescence intensity is weakly dependent on the Schottky barrier height or polarity of the contact. We fabricate a monolayer seven-segment display and achieve the first transparent and bright millimeter-scale light-emitting monolayer semiconductor device.Atomically thin monolayers with high photoluminescence quantum yield are promising for optoelectronic and lighting applications. Here, the authors fabricate a transient-mode electroluminescent device to bypass the requirement of ohmic contacts for electrons and holes, and observe millimetre-scale light emission from a transparent 2D display.

Optical antenna-enhanced nano-LED for energy efficient optical interconnect

Interconnects accounts for a significant portion of energy consumption in integrated circuits. Optical interconnects, now widely used to link electronic systems such as servers and top of rack switches in data centers, can potentially reduce the energy consumption of electrical interconnects. However, current state-of-the-art optical links consumes about 100s fJ/b to 1 pJ/b, still much too high for on-chip communications [1]. Orders of magnitude improvement in energy efficiency can be achieved by combining (1) ultra-low capacitance optical receivers and (2) optical antenna-enhanced nanoscale light-emitting diodes (LED). By reducing the receiver capacitance to ~ 100 aF [2] and preferably integrating the detector with the first gain stage forming a phototransistor [3][4], the energy consumption of the photoreceiver can be reduced to ~ 100 aJ/b even with 100 photons/bit sensitivity. However, traditional laser source consumes too much power due to the need to bias the laser, usually at several times the threshold current. Light emitting diodes (LEDs), on the other hand, can operate efficiently without threshold. Unfortunately, their modulation speeds are limited by the relatively slow spontaneous emission. Recently, progress has been made using optical antennas to increase the rate of spontaneous emission, opening up the possibility of an efficient, high speed, nanoscale emitter. We have observed 35x enhancement of spontaneous emission rate in optically pumped InGaAsP nano-LEDs with arch-dipole antennas [5]. Recently, using cavity-backed optical slot antennas, electrically injected nano-LEDs with 200x enhancement of spontaneous emission rate have been demonstrated [6]. Even higher enhancement has been observed in nano-LEDs with monolayer two-dimensional semiconductor such as transition metal dichalcogenide, WSe2 [7]. In this talk, we will review the principle and the recent progress in optical antenna-enhanced nano-LEDs.