Search query: Atomically thin p–n junctions with van der Waals hetero- interfaces

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abstract: Semiconductor p n junctions are essential building blocks for electronic and optoelectronic devices. In conventional p n junctions, regions depleted of free charge carriers form on either side of the junction, generating built in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes influenced by the spatial extent of this depletion region. With the advent of atomically thin van der Waals materials and their heterostructures, it is now possible to realize a p n junction at the ultimate thickness limit. Van der Waals junctions composed of p and n type semiconductors each just one unit cell thick are predicted to exhibit completely different charge transport characteristics than bulk heterojunctions. Here, we report the characterization of the electronic and optoelectronic properties of atomically thin p n heterojunctions fabricated using van der Waals assembly of transition metal dichalcogenides. We observe gate tunable diode like current rectification and a photovoltaic response across the p n interface. We find that the tunnelling assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p n junction between graphene layers enhances the collection of the photoexcited carriers. The atomically scaled van der Waals p n heterostructures presented here constitute the ultimate functional unit for nanoscale electronic and optoelectronic devices.
author_names: Chul-Ho Lee

Gwan-Hyoung Lee

Arend M van der Zande

Wenchao Chen

Yilei Li

Minyong Han

Xu Cui

Ghidewon Arefe

Colin P Nuckolls

Tony F Heinz

Jing Guo

James C Hone

Philip Kim
title: Atomically thin p n junctions with van der Waals heterointerfaces.
venue: Nature nanotechnology
year: 2014

abstract: We report on a new chemical sensor based on black phosphorus/molybdenum diselenide van der Waals hetero junctions. Due to the atomically thin nature of two dimensional (2D) materials, surface adsorption of gas molecules can effectively modulate the band alignment at the junction interface, making the device a highly sensitive detector for chemical adsorptions. Compared to sensors made of homogeneous nanomaterials, the hetero junction demonstrates considerably lower detection limit and higher sensitivity toward nitrogen dioxide. Kelvin probe force microscopy and finite element simulations have provided experimental and theoretical explanations for the enhanced performance, proving that chemical adsorption can induce significant changes in band alignment and carrier transport behaviors. The study demonstrates the potential of van der Waals hetero junction as a new platform for sensing applications, and provides more insights into the interaction between gaseous molecules and 2D hetero structures.
author_names: Zhihong Feng

Buyun Chen

Shuangbei Qian

Linyan Xu

Liefeng Feng

Yuanyuan Yu

Rui Zhang

Jiancui Chen

Qianqian Li

Quanning Li

Chongling Sun

Hao Zhang

Jing Liu

Wei Pang

Daihua Zhang
title: Chemical sensing by band modulation of a black phosphorus/molybdenum diselenide van der Waals hetero structure
year: 2016

abstract: Abstract Atomically thin vertically stacked 2D vdW heterostructures have recently emerged as a new kind of device with intriguing novel phenomena for both academic and industrial interests. However, the lack of p type materials remains a challenging issue to create useful devices for the realization of practical applications. Here, we demonstrate the first vertically stacked few layered p type GaSe and n type SnS2 vdW heterostructure for high performance optoelectronic applications. It is found that the phototransistors based on a few layered GaSe/SnS2 p n junction show superior performance with the responsivity, EQE and specific detectivity as high as ~35 AW 1, 62% and 8.2 x 1013 J, respectively, which exceed all the reported values derived from 2D materials. Also, the GaSe/SnS2 p n junction can serve as a photovoltaic cell with a high power conversion efficiency of about ~2.84% Moreover, the heterostructures can be deposited on flexible PET substrates with excellent performance. Through a detailed study, the underlying mechanism responsible for the high performance can be attributed to the unique type II band alignment and excellent quality of the interface. The heterojunctions presented in this work demonstrate a new illustration for the stacking of 2D materials, which is very useful for the development of next generation novel optoelectronic devices.
author_names: Packiyaraj Perumal

Rajesh Kumar Ulaganathan

Raman Sankar

Ling Zhu
title: Staggered band offset induced high performance opto electronic devices: Atomically thin vertically stacked GaSe SnS2 van der Waals p n heterostructures
year: 2021

abstract: In nano device applications using two dimensional (2D) van der Waals materials, a heat dissipation through nano scale interfaces can be a critical issue for optimizing device performances. By using a time domain thermoreflectance measurement technique, we examine a cross plane thermal transport through mono layered (n 1) and bi layered (n 2) WSe2 flakes which are sandwiched by top metal layers of Al, Au, and Ti and the bottom Al2O3 substrate. In these nanoscale structures with hetero and homo junctions, we observe that the thermal boundary resistance (TBR) is significantly enhanced as the number of WSe2 layers increases. In particular, as the metal is changed from Al, to Au, and to Ti, we find an interesting trend of TBR depending on the WSe2 thickness; when referenced to TBR for a system without WSe2, TBR for n 1 decreases, but that for n 2 increases. This result clearly demonstrates that the stronger bonding for Ti leads to a better thermal conduction between the metal and the WSe2 layer, but in return gives rise to a large mismatch in the phonon density of states between the first and second WSe2 layers so that the WSe2 WSe2 interface becomes a major thermal resistance for n 2. By using photoemission spectroscopy and optical second harmonic generation technique, we confirm that the metallization induces a change in the valence state of W ions, and also recovers a non centrosymmetry for the bi layered WSe2.
author_names: Young-Gwan Choi

Do-Gyeom Jeong

Hwiin Ju

Chang Jae Roh

Geonhwa Kim

Bongjin Simon Mun

Tae Yun Kim

Sang-Woo Kim

Jong Sung Lee
title: Covalent bonding induced strong phonon scattering in the atomically thin WSe2 layer
venue: Scientific Reports
year: 2019

abstract: The two dimensional limit of layered materials has recently been realized through the use of van der Waals (vdW) heterostructures composed of weakly interacting layers. In this paper, we describe two different classes of vdW heterostructures: inorganic vdW heterostructures prepared by co lamination and restacking; and organic inorganic hetero epitaxy created by physical vapor deposition of organic molecule crystals on an inorganic vdW substrate. Both types of heterostructures exhibit atomically clean vdW interfaces. Employing such vdW heterostructures, we have demonstrated various novel devices, including graphene/hexagonal boron nitride (hBN) and MoS2 heterostructures for memory devices; graphene/MoS2/WSe2/graphene vertical p n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high performance transistors.
author_names: Gwan-Hyoung Lee

Chul-Ho Lee

Arend van der Zande

Minyong Han

Xu Cui

Ghidewon Arefe

Colin P Nuckolls

Tony F Heinz

James C Hone

Philip Kim
title: Heterostructures based on inorganic and organic van der Waals systems
year: 2014

abstract: Graphene/two dimensional (2D) semiconductor heterostructures have been demonstrated to possess many advantages for electronic and optoelectronic devices. However, there are few reports about the utilization of a 2D semiconductor monolayer to tune the properties of graphene. Here, we report the fabrication and characterization of graphene p n junctions based on graphene/MoS2 hybrid interfaces. Monolayered graphene across the monolayered MoS2 boundary is divided into n type regions on the MoS2 and p type regions on the SiO2 substrate. Such van der Waals heterostructure based graphene p n junctions show good photoelectric properties. The photocurrent modulation of such devices by a single back gate is also demonstrated for the first time, which shows that the graphene on and off MoS2 regions have different responses to the gate voltage. Our results suggest that the atomic thin hybrid structure can remarkably extend the device applications.
author_names: Jie Meng

Huading Song

Caizhen Li

Yibo Jin

Lei Tang

Dameng Liu

Zhimin Liao

Faxian Xiu

Daqing Yu
title: Lateral graphene p n junctions formed by the graphene/MoS2 hybrid interface.
venue: Nanoscale
year: 2015

abstract: Atomically thin and sharp van der Waals heterojunction can be created by vertically stacking p type monolayer tungsten diselenide (WSe2) onto n type molybdenum disulfide (MoS2) Theory predicts that stacked MoS2 and WSe2 monolayer forms type II p n junction, creating a built in electric field across the interface which facilitates electron hole separation and transfer. Gaining insights into the dynamics of charge transfer across van der Waals heterostructure is central to understanding light photocurrent conversion at these ultrathin interfaces. Herein, we investigate the exciton dissociation and charge transfer in a MoS2/WSe2 van der Waals hetero structure. Our results show that ultrafast electron transfer from WSe2 to MoS2 take place within 470 fs upon optical excitation with 99% charge transfer efficiency, leading to drastic photoluminescence quenching and decreased lifetime. Our findings suggest that van der Waals heterostructure may be useful as active components in ultrafast optoelectronic devices.
author_names: Bo Peng

Guannan Yu

Xinfeng Liu

Bo Liu

Xiao Liang

Lei Bi

Longjiang Deng

Tze Chien Sum

Kian Ping Loh
title: Ultrafast charge transfer in MoS 2 /WSe 2 p n Heterojunction
year: 2016

abstract: Synthesized two dimensional GaSe/MoSe2 misfit heterostructures form p n junctions with a gate tunable photovoltaic response. Two dimensional (2D) heterostructures hold the promise for future atomically thin electronics and optoelectronics because of their diverse functionalities. Although heterostructures consisting of different 2D materials with well matched lattices and novel physical properties have been successfully fabricated via van der Waals (vdW) epitaxy, constructing heterostructures from layered semiconductors with large lattice misfits remains challenging. We report the growth of 2D GaSe/MoSe2 heterostructures with a large lattice misfit using two step chemical vapor deposition (CVD) Both vertically stacked and lateral heterostructures are demonstrated. The vertically stacked GaSe/MoSe2 heterostructures exhibit vdW epitaxy with well aligned lattice orientation between the two layers, forming a periodic superlattice. However, the lateral heterostructures exhibit no lateral epitaxial alignment at the interface between GaSe and MoSe2 crystalline domains. Instead of a direct lateral connection at the boundary region where the same lattice orientation is observed between GaSe and MoSe2 monolayer domains in lateral GaSe/MoSe2 heterostructures, GaSe monolayers are found to overgrow MoSe2 during CVD, forming a stripe of vertically stacked vdW heterostructures at the crystal interface. Such vertically stacked vdW GaSe/MoSe2 heterostructures are shown to form p n junctions with effective transport and separation of photogenerated charge carriers between layers, resulting in a gate tunable photovoltaic response. These GaSe/MoSe2 vdW heterostructures should have applications as gate tunable field effect transistors, photodetectors, and solar cells.
author_names: Xufan Li

Ming-Wei Lin

Junhao Lin

Bing Huang

Alexander A Puretzky

Cheng Ma

Kai Wang

Wu Zhou

Sokrates T Pantelides

Miaofang Chi

Ivan I Kravchenko

Jason D Fowlkes

Christopher M Rouleau

David B Geohegan

Kai Xiao
title: Two dimensional GaSe/MoSe2 misfit bilayer heterojunctions by van der Waals epitaxy
venue: Science Advances
year: 2016

abstract: Description
author_names: Tiancheng Song

Eric Anderson

Matisse Wei-Yuan Tu

Kyle L Seyler

Takashi Taniguchi

Kenji Watanabe

Michael A McGuire

Xiaosong Li

Ting Cao

Di Xiao

Wang Yao

Xiaodong Xu
title: Spin photovoltaic effect in magnetic van der Waals heterostructures
venue: Science advances
year: 2021

abstract: van der Waals junctions of two dimensional materials with an atomically sharp interface open up unprecedented opportunities to design and study functional heterostructures. Semiconducting transition metal dichalcogenides have shown tremendous potential for future applications due to their unique electronic properties and strong light matter interaction. However, many important optoelectronic applications, such as broadband photodetection, are severely hindered by their limited spectral range and reduced light absorption. Here, we present a p g n heterostructure formed by sandwiching graphene with a gapless band structure and wide absorption spectrum in an atomically thin p n junction to overcome these major limitations. We have successfully demonstrated a MoS2 graphene WSe2 heterostructure for broadband photodetection in the visible to short wavelength infrared range at room temperature that exhibits competitive device performance, including a specific detectivity of up to 10(11) Jones in the near infrared region. Our results pave the way toward the implementation of atomically thin heterostructures for broadband and sensitive optoelectronic applications.
author_names: Mingsheng Long

Erfu Liu

Peng Jie Wang

Anyuan Gao

Hui Xia

Wei Luo

Baigeng Wang

Junwen Zeng

Yajun Fu

Kang Xu

Wei Zhou

Yangyang Lv

Shu-hua Yao

Minghui Lu

Yanfeng Chen

Zhenhua Ni

Yumeng You

Xueao Zhang

Shiqiao Qin

Yi Shi

Weida Hu

Ding-yu Xing

Feng Miao
title: Broadband Photovoltaic Detectors Based on an Atomically Thin Heterostructure.
venue: Nano letters
year: 2016