Environment-insensitive and gate-controllable photocurrent enabled by bandgap engineering of MoS2 junctions

Abstract

Two-dimensional (2D) materials are composed of atomically thin crystals with an enormous surface-to-volume ratio, and their physical properties can be easily subjected to the change of the chemical environment. Encapsulation with other layered materials, such as hexagonal boron nitride, is a common practice; however, this approach often requires inextricable fabrication processes. Alternatively, it is intriguing to explore methods to control transport properties in the circumstance of no encapsulated layer. This is very challenging because of the ubiquitous presence of adsorbents, which can lead to charged-impurity scattering sites, charge traps, and recombination centers. Here, we show that the short-circuit photocurrent originated from the built-in electric field at the MoS2 junction is surprisingly insensitive to the gaseous environment over the range from a vacuum of 1 × 10−6 Torr to ambient condition. The environmental insensitivity of the short-circuit photocurrent is attributed to the characteristic of the diffusion current that is associated with the gradient of carrier density. Conversely, the photocurrent with bias exhibits typical persistent photoconductivity and greatly depends on the gaseous environment. The observation of environment-insensitive short-circuit photocurrent demonstrates an alternative method to design device structure for 2D-material-based optoelectronic applications.

Role of Hole Trap Sites in MoS2 for Inconsistency in Optical and Electrical Phenomena

“…The fitting (solid lines in the inset of Figure d) yields β = 0.63 and 0.75, and τ = 116 and 87 s for the MoS 2 /SiO 2 and MoS 2 /h-BN samples, respectively. τ and β for MoS 2 /SiO 2 are consistent with the values reported in the literature. , The higher relaxation time of MoS 2 /SiO 2 implies a larger disorder or a larger amount of traps. , It is challenging to determine whether the time delay for the sample on the SiO 2 substrate is caused by the rugged valence band edge or by the trapped electrons at the MoS 2 /SiO 2 interface.…”

“…This delayed phenomenon is governed by the relaxation of the excess electrons in the conduction band to hole-trapped sites. It is called persistent photoconductivity (PPC) and normally occurs in highly disordered semiconductors and heterojunctions. ,, The PPC relaxation behavior can be well-described by a stretched exponential function, ,, where β is the decay exponent (0 ≤ β ≤ 1) and τ is the relaxation time constant. The fitting (solid lines in the inset of Figure d) yields β = 0.63 and 0.75, and τ = 116 and 87 s for the MoS 2 /SiO 2 and MoS 2 /h-BN samples, respectively.…”

Hyaluronan, Cancer-Associated Fibroblasts and the Tumor Microenvironment in Malignant Progression

“…HA is a simple extracellular matrix polysaccharide that a wealth of experimental approaches has demonstrated is an instructive factor in cancer initiation and progression (Heldin et al, 2014 ; Tolg et al, 2014 ; Zhang C. et al, 2015 ; Chanmee et al, 2016 ; Turley et al, 2016 ; Bohaumilitzky et al, 2017 ; Senbanjo and Chellaiah, 2017 ; Shih et al, 2017 ; Wight, 2017 ; Wong et al, 2017 ). For example, blocking HA synthesis (Itano et al, 2008 ; Hamada et al, 2017 ; Ikuta et al, 2017 ) or ablating the HA-binding function of one of its receptors RHAMM (gene name HMMR) (Hall et al, 1995 ), which has been strongly linked to tumorigenesis (Tolg et al, 2014 ; Turley et al, 2016 ), attenuates the transformed phenotype.…”

Retinomorphic optoelectronic devices for intelligent machine vision

“…The excellent photoelectric response characteristics and inherent persistent photoconductivity (PPC) effect or retention characteristic regulated by external fields endow 2D materials-based devices image perception and long-term memory functions ( Kallatt et al., 2018 ; Shih et al., 2017 ). Because the conductance state of the 2D material-based transistor channel can be effectively adjusted by external stimuli, such as light, voltage bias, and magnetic field, the 2D materials-based photoelectric sensor array can perform an efficient image recognition function in situ when combined with an artificial neural network.…”