Superior Plasmonic Photodetectors Based on Au@MoS2 Core–Shell

www.acsnano.org

Superior Plasmonic Photodetectors Based on Au@MoS2 Core−Shell Heterostructures Yuan Li,†,‡ Jennifer G. DiStefano,†,§ Akshay A. Murthy,† Jeffrey D. Cain,†,§ Eve D. Hanson,†,§ Qianqian Li,†,‡ Fernando C. Castro,† Xinqi Chen,*,‡,∥ and Vinayak P. Dravid*,†,‡,§ †

Department of Materials Science and Engineering, ‡Northwestern University Atomic and Nanoscale Characterization Experimental (NUANCE) Center, §International Institute for Nanotechnology (IIN), and ∥Department of Mechanical Engineering, Northwestern University, Evanston, Illinois 60208, United States S Supporting Information *

ABSTRACT: Integrating plasmonic materials into semiconductor media provides a promising approach for applications such as photosensing and solar energy conversion. The resulting structures introduce enhanced light− matter interactions, additional charge trap states, and efficient charge-transfer pathways for light-harvesting devices, especially when an intimate interface is built between the plasmonic nanostructure and semiconductor. Herein, we report the development of plasmonic photodetectors using Au@MoS2 heterostructuresan Au nanoparticle core that is encapsulated by a CVDgrown multilayer MoS2 shell, which perfectly realizes the intimate and direct interfacing of Au and MoS2. We explored their favorable applications in different types of photosensing devices. The first involves the development of a large-area interdigitated field-effect phototransistor, which shows a photoresponsivity ∼10 times higher than that of planar MoS2 transistors. The other type of device geometry is a Si-supported Au@MoS2 heterojunction gateless photodiode. We demonstrated its superior photoresponse and recovery ability, with a photoresponsivity as high as 22.3 A/W, which is beyond the most distinguished values of previously reported similar gateless photodetectors. The improvement of photosensing performance can be a combined result of multiple factors, including enhanced light absorption, creation of more trap states, and, possibly, the formation of interfacial charge-transfer transition, benefiting from the intimate connection of Au and MoS2. KEYWORDS: Au@MoS2, core−shell, heterostructures, plasmonic enhancement, photodetectors matter interaction of materials.9,10 When embedded within a semiconductor, these nanostructures trigger the redistribution, localization, and enhancement of the electromagnetic field by coupling with the incident light at the frequency of localized surface plasmon resonance (LSPR). The light absorption of surrounding materials can be improved via both the near-field electromagnetic field enhancement and the increase of optical path length caused by light scattering of the nanostructures.11 Such amplification of light absorption has been shown to be a key advantage in photosensing devices.12 Moreover, the incident light can be coupled with surface plasmons of the noble metal nanostructures embedded in a semiconductor device. The subsequent nonradiative decay of the plasmons results in the creation of so-called energetic “hot electrons”. The further injection of such “hot electrons” across the Schottky barrier at the metal−semiconductor interface leads to

M

olybdenum disulfide (MoS2), a semiconductor in the family of transition metal dichalcogenide (TMD) materials, has recently drawn great research interest in a wide range of applications such as electronic transistors, light sensing, biomedical imaging, and spectroscopies.1−3 MoS2 monolayers have been considered as a promising candidate material for photodetectors due to their interesting transistor behaviors (e.g., high ON/OFF ratio)1 and direct band gap nature.4,5 A photosensing field-effect transistor (namely, phototransistor) initially made from monolayer MoS2 was reported with a low photoresponsivity value of 7.5 mA W−1.6 Higher responsivity was then achieved up to 880 A W−1 by improving the device fabrication technologies. However, this value was only achieved by using a large gate voltage and ultrasmall illumination power and, moreover, by largely sacrificing the response and recovery time.7 It is also reported that the optical cross section of monolayer MoS2 is low, which thus inhibits its light−matter interactions and leads to weak absorption.8 Use of light-trapping properties of plasmonic nanostructures (e.g., Au, Ag) is an important approach to improve the light− © 2017 American Chemical Society

Received: July 18, 2017 Accepted: September 21, 2017 Published: September 21, 2017 10321

DOI: 10.1021/acsnano.7b05071 ACS Nano 2017, 11, 10321−10329

Article

Cite This: ACS Nano 2017, 11, 10321-10329

Article

ACS Nano the generation of photocurrent response but with a very low photoresponsivity (