https://absimage.aps.org/image/MAR14/MWS_MAR14-2014-020819.pdf

Van der Waals heterostructures

Near-infrared (NIR) solid-state micro/nanolasers are important building blocks for true integration of optoelectronic circuitry.1 Although significant progress has been made in III–V nanowire lasers with achieving NIR lasing at room temperature,2−4 challenges remain including low quantum efficiencies and high Auger losses. Importantly, the obstacles toward integrating one-dimensional nanowires on the planar ubiquitous Si platform need to be effectively tackled. Here we demonstrate a new family of planar room-temperature NIR nanolasers based on organic–inorganic perovskite CH3NH3PbI3-aXa (X = I, Br, Cl) nanoplatelets. Their large exciton binding energies, long diffusion lengths, and naturally formed high-quality planar whispering-gallery mode cavities ensure adequate gain and efficient optical feedback for low-threshold optically pumped in-plane lasing. We show that these remarkable wavelength tunable whispering-gallery nanolasers can be easily integrated onto conductive platforms (Si, Au, indium tin oxide...

Room-temperature near-infrared high-Q perovskite whispering-gallery planar nanolasers.

Optics offers unique opportunities for reducing energy in information processing and communications while simultaneously resolving the problem of interconnect bandwidth density inside machines. Such energy dissipation overall is now at environmentally significant levels; the source of that dissipation is progressively shifting from logic operations to interconnect energies. Without the prospect of substantial reduction in energy per bit communicated, we cannot continue the exponential growth of our use of information. The physics of optics and optoelectronics fundamentally addresses both interconnect energy and bandwidth density, and optics may be the only scalable solution to such problems. Here we summarize the corresponding background, status, opportunities, and research directions for optoelectronic technology and novel optics, including subfemtojoule devices in waveguide and novel two-dimensional (2-D) array optical systems. We compare different approaches to low-energy optoelectronic output devices and their scaling, including lasers, modulators and LEDs, optical confinement approaches (such as resonators) to enhance effects, and the benefits of different material choices, including 2-D materials and other quantum-confined structures. With such optoelectronic energy reductions, and the elimination of line charging dissipation by the use optical connections, the next major interconnect dissipations are in the electronic circuits for receiver amplifiers, timing recovery, and multiplexing. We show we can address these through the integration of photodetectors to reduce or eliminate receiver circuit energies, free-space optics to eliminate the need for timing and multiplexing circuits (while also solving bandwidth density problems), and using optics generally to save power by running large synchronous systems. One target concept is interconnects from ∼1 cm to ∼10 m that have the same energy (∼10 fJ/bit) and simplicity as local electrical wires on chip.

Attojoule Optoelectronics for Low-Energy Information Processing and Communications

Two-dimensional (2D) materials have generated great interest in the past few years as a new toolbox for electronics. This family of materials includes, among others, metallic graphene, semiconducting transition metal dichalcogenides (such as MoS2), and insulating boron nitride. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency, and favorable transport properties for realizing electronic, sensing, and optical systems on arbitrary surfaces. In this paper, we demonstrate a novel technology for constructing large-scale electronic systems based on graphene/molybdenum disulfide (MoS2) heterostructures grown by chemical vapor deposition. We have fabricated high-performance devices and circuits based on this heterostructure, where MoS2 is used as the transistor channel and graphene as contact electrodes and circuit interconnects. We provide a systematic comparison of the graphene/MoS2 heterojunction contact to more traditional MoS2-metal junctions, as well as a theoretical investigation, using density functional theory, of the origin of the Schottky barrier height. The tunability of the graphene work function with electrostatic doping significantly improves the ohmic contact to MoS2. These high-performance large-scale devices and circuits based on this 2D heterostructure pave the way for practical flexible transparent electronics.

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Graphene-MoS2 Hybrid Technology for Large-Scale Two-Dimensional Electronics

2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

Monolayer transition-metal dichalcogenides (TMDs) have the potential to become efficient optical-gain materials for low-energy-consumption nanolasers with the smallest gain media because of strong excitonic emission. However, until now TMD-based lasing has been realized only at low temperatures. Here we demonstrate for the first time a room-temperature laser operation in the infrared region from a monolayer of molybdenum ditelluride on a silicon photonic-crystal cavity. The observation is enabled by the unique combination of a TMD monolayer with an emission wavelength transparent to silicon, and a high-Q cavity of the silicon nanobeam. The laser is pumped by a continuous-wave excitation, with a threshold density of 6.6 W cm-2. Its linewidth is as narrow as 0.202 nm with a corresponding Q of 5,603, the largest value reported for a TMD laser. This demonstration establishes TMDs as practical materials for integrated TMD-silicon nanolasers suitable for silicon-based nanophotonic applications in silicon-transparent wavelengths.

Room-temperature continuous-wave lasing from monolayer molybdenum ditelluride integrated with a silicon nanobeam cavity

Rare-earth optical materials with large optical gain are of great importance for a wide variety of applications in photonics and quantum information due to their long carrier lifetimes and quantum coherence times, especially in the realization of efficient lasers and amplifiers. Until now, such materials have achieved a gain of less than a few dB cm–1, rendering them unsuitable for applications in nanophotonic integrated circuits. Here, we report the results of the signal enhancement and transmission experiments on a single-crystal erbium chloride silicate nanowire. Our experiments demonstrate that a net material gain over 100 dB cm–1 at wavelengths around 1,530 nm is possible due to the nanowire's single-crystalline material quality and its high erbium concentration. Our results establish that such rare-earth-compound nanowires are a potentially important class of nanomaterials for a variety of applications including, for example, subwavelength-scale optical amplifiers and lasers for integrated nanophotonics, and quantum information. Erbium chloride silicate nanowire promises optical gain for nanophotonic circuits.

Giant optical gain in a single-crystal erbium chloride silicate nanowire

Nanoscale self-assembly offers a pathway to realize heterogeneous integration of III–V materials on silicon. However, for III–V nanowires directly grown on silicon, dislocation-free single-crystal quality could only be attained below certain critical dimensions. We recently reported a new approach that overcomes this size constraint, demonstrating the growth of single-crystal InGaAs/GaAs and InP nanoneedles with the base diameters exceeding 1 μm. Here, we report distinct optical characteristics of InP nanoneedles which are varied from mostly zincblende, zincblende/wurtzite-mixed, to pure wurtzite crystalline phase. We achieved, for the first time, pure single-crystal wurtzite-phase InP nanoneedles grown on silicon with bandgaps of 80 meV larger than that of zincblende-phase InP. Being able to attain excellent material quality while scaling up in size promises outstanding device performance of these nanoneedles. At room temperature, a high internal quantum efficiency of 25% and optically pumped lasing are ...

Tailoring the optical characteristics of microsized InP nanoneedles directly grown on silicon.

Effect of CdCl2 annealing treatment on thin CdS films prepared by chemical bath deposition

Future expansion of computing capabilities relies on a reduction of energy consumption in silicon-based integrated circuits. A promising solution is to replace electrical wires with optical connections, for which a key component is a nanolaser that coherently emits into silicon-based waveguides to route information across a chip, in place of bulky off-chip devices. We report room temperature, sub-μm2 footprint, quantum-well-in-nanopillar lasers grown directly on silicon and silicon-on-insulator (SOI) substrates that emit within the silicon-transparent wavelength range under optical excitation. The laser wavelength is controlled by changing the InGaAs quantum well thickness and alloy composition, quite independent of lattice mismatch with the InP barrier, a unique property of the 3D core-shell growth mode. We achieve excellent luminescence yield and low continuous wave transparency power due to the well-passivated InGaAs/InP interfaces. These sub-μm2 footprint long-wavelength lasers could enable optoelectronic integration and photon routing with silicon waveguides on the technologically relevant SOI platform.

Hao Sun

Papers

Room-temperature continuous-wave lasing from monolayer molybdenum ditelluride integrated with a silicon nanobeam cavity

Giant optical gain in a single-crystal erbium chloride silicate nanowire

Tailoring the optical characteristics of microsized InP nanoneedles directly grown on silicon.

Effect of CdCl2 annealing treatment on thin CdS films prepared by chemical bath deposition

Nanopillar quantum well lasers directly grown on silicon and emitting at silicon-transparent wavelengths