Optoelectronic devices based on electrically tunable p–n diodes in a monolayer dichalcogenide

Abstract

One of the most fundamental devices for electronics and optoelectronics is the PN junction, which provides the functional element of diodes, bipolar transistors, photodetectors, LEDs, and solar cells, among many other devices. In conventional PN junctions, the adjacent p-and ntype regions of a semiconductor are formed by chemical doping. Materials with ambipolar conductance, however, allow for PN junctions to be configured and modified by electrostatic gating. This electrical control enables a single device to have multiple functionalities. Here we report ambipolar monolayer WSe 2 devices in which two local gates are used to define a PN junction exclusively within the sheet of WSe 2 . With these electrically tunable PN junctions, we demonstrate both PN and NP diodes with ideality factors better than 2. Under excitation with light, the diodes show photodetection responsivity of 210 mA/W and photovoltaic power generation with a peak external quantum efficiency of 0.2%, promising numbers for a nearly transparent monolayer sheet in a lateral device geometry. Finally, we demonstrate a lightemitting diode based on monolayer WSe 2 . These devices provide a fundamental building block for ubiquitous, ultra-thin, flexible, and nearly transparent optoelectronic and electronic applications based on ambipolar dichalcogenide materials.Next generation photodetectors and photovoltaic devices, as well as sensors, displays, and light emitting diodes, will all require new optoelectronic materials with superior characteristics to those currently in use. Candidate materials must be flexible for wearable devices, transparent for interactive displays, efficient for solar cells, and robust and low cost for broad distribution. Monolayer semiconducting transition metal dichalcogenides (TMDs) such as tungsten diselenide (WSe 2 ) are flexible 1 , nearly transparent 2,3 , high strength 1 , direct band gap 2 materials that have the potential to meet all of these criteria. Tungsten diselenide's crystal structure is comprised of stacks of trilayer sheets made of a single atomic layer of tungsten encapsulated by two layers of selenium. This structure leads to very strong intralayer bonding in the trilayer plane and weak interlayer bonding * These authors contributed equally to this work.arXiv:1310.0452v2 [cond-mat.mes-hall]

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS2/MoSe2/MoS2 Trilayer van der Waals Heterostructures

“…[1][2][3][4][5][6][7][8][9][10] The bandgap of monolayer TMDCs occurs at the inequivalent (but degenerate) K and K' points of the hexagonal Brillouin zone. The broken inversion symmetry of a TMDC monolayer combined with the time reversal symmetry imposes opposite magnetic moments at the K and K' valleys.…”

High Electrical Conductivity in Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2, a Semiconducting Metal–Organic Graphene Analogue

“…The former can be deposited as largearea single sheets in a "top-down" approach. 10,11 They have been shown to perform well in device testing, [12][13][14] but do not easily lend themselves to chemical functionalization and tunability. In contrast, COFs are prepared by "bottom-up" solution-based synthetic methods and are attractive because they are subject to rational modification.…”

Interlayer‐State‐Coupling Dependent Ultrafast Charge Transfer in MoS2/WS2 Bilayers

“…Since the discovery of graphene and the rise of MoS 2 as well as black phosphorus, atomically thin 2D crystals have grown into a huge family of materials ranging from semimetal, semiconductors to insulators 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. Monolayer transition‐metal dichalcogenides denoted as MX 2 (e.g., M = Mo, W, and X = S, Se, Te), have been prepared by physical exfoliation and chemical vapor deposition, providing more choices for 2D materials.…”

“…Monolayer transition‐metal dichalcogenides denoted as MX 2 (e.g., M = Mo, W, and X = S, Se, Te), have been prepared by physical exfoliation and chemical vapor deposition, providing more choices for 2D materials. The MX 2 materials share similar crystalline structures and symmetries, but possess distinct electronic properties in bandgaps, photoabsorption, and spin–orbit coupling strength 7, 8, 9. The heterostructures vertically reassembled from different 2D materials form even richer material systems, and thus provide a new platform for investigating new physics12, 13, 14, 15, 16 and exploring new applications 17, 18, 19, 20, 21, 22, 23, 24.…”