Ultrafast Monolayer In/Gr-WS₂-Gr Hybrid Photodetectors with High Gain

Abstract

One of the primary limitations of previously reported two-dimensional (2D) photodetectors is a low frequency response (≪ 1 Hz) for sensitive devices with gain. Yet, little efforts have been devoted to improve the temporal response of photodetectors while maintaining high gain and responsivity. Here, we demonstrate a gain of 6.3 × 10 3 electrons per photon and a responsivity of 2.6 × 10 3 A/W while simultaneously exhibiting an ultrafast response time of 40−65 μs in a hybrid photodetector that consists of graphene-WS 2 -graphene junctions covered with indium (In) adatoms atop. The resultant responsivity is 6 orders of magnitude higher than that of conventional photodetectors comprising solely of a Au-WS 2 -Au junction. The photogain is provided mainly by the adsorbed In adatoms, from which photogenerated electrons can be transferred to the WS 2 channel, while holes remain trapped in In adatoms, leading to a photogating effect as electrons are recirculating during the residence of holes in In adatoms. At a gate voltage near the Dirac point of graphene, a detectivity of D* = 2.2 × 10 12 Jones and an ON/OFF ratio of 10 4 are achieved. The enhanced performance of the device can be attributed partly to the transparent graphene/WS 2 contact and partly to the strong capacitive coupling of the In adatoms with the WS 2 channel, which enables ultrafast carrier dynamics.

High‐Performance Flexible Broadband Photodetectors Based on 2D Hafnium Selenosulfide Nanosheets

“…We have also calculated the photoresponsivity ( R λ ) and specific detectivity ( D *) of the HSS phototransistor, which are important factors to appraise the sensitivity of photodetectors. Photoresponsivity ( R λ ) is defined by the photocurrent generated per incident photon as R λ = I ph / P λ S, where I ph is the generated photocurrent, P λ is the incident photon density, and S is the illuminated area of the device . Figure f shows the calculated photoresponsivity, which is sublinear with respect to the incident photon.…”

“…Photoresponsivity (R λ ) is defined by the photocurrent generated per incident photon as R λ = I ph /P λ S, where I ph is the generated photocurrent, P λ is the incident photon density, and S is the illuminated area of the device. [34,35] Figure 4f shows the calculated photoresponsivity, which is sublinear with respect to the incident photon. Remarkably, we have achieved giant photoresponsivity of ≈6.4 × 10 4 A W −1 at 9.2 µW cm −2 of 488 nm (V g = 0 V and V ds = 10 V), which is about 10 5 orders magnitude higher than the reported HfS 2(1−x) Se 2x alloy prepared by the CVD method, [28] and also greater than other HfS 2 -and HfSe 2based photodetectors, [21][22][23][24] as compared to Table S2, Supporting Information.…”

Band Alignment Engineering in Two‐Dimensional Transition Metal Dichalcogenide‐Based Heterostructures for Photodetectors

“…Reproduced with permission. [ 76 ] Copyright 2019, American Chemical Society. i) Schematic showing h‐BN/MoTe 2 /graphene/SnS 2 /h‐BN device configuration.…”

Selective Growth of WSe2 with Graphene Contacts

“…Recently, integration of conductive graphene and semiconducting TMD for improved contacts and novel properties is realized by direct growth of TMD using chemical vapor deposition at the edge of artificially patterned graphene [14][15][16][17][18][19][20][21]. Heterojunctions among different 2D materials enable essential multifunctionality of the monolayer channels for broader capacity and integration [22][23][24][25][26][27]. Weak tunneling barrier is achieved at the heterojunction of the laterally stitched MoS 2 -graphene, enabling inverter and negative-AND (NAND) gates for a complete set of logic circuits based on 2D materials [16,17].…”