Investigation of Band-Offsets at Monolayer–Multilayer MoS₂ Junctions by Scanning Photocurrent Microscopy

Abstract

The thickness-dependent band structure of MoS2 implies that discontinuities in energy bands exist at the interface of monolayer (1L) and multilayer (ML) thin films. The characteristics of such heterojunctions are analyzed here using current versus voltage measurements, scanning photocurrent microscopy, and finite element simulations of charge carrier transport. Rectifying I-V curves are consistently observed between contacts on opposite sides of 1L/ML junctions, and a strong bias-dependent photocurrent is observed at the junction. Finite element device simulations with varying carrier concentrations and electron affinities show that a type II band alignment at single layer/multilayer junctions reproduces both the rectifying electrical characteristics and the photocurrent response under bias. However, the zero-bias junction photocurrent and its energy dependence are not explained by conventional photovoltaic and photothermoelectric mechanisms, indicating the contributions of hot carriers.

Low-Resistance 2D/2D Ohmic Contacts: A Universal Approach to High-Performance WSe2, MoS2, and MoSe2 Transistors

“…However, this band alignment along the vertical direction in region I creates a band offset along the lateral direction parallel to the channel. 46 In summary, we have developed a novel 2D/2D contact strategy to achieve high-quality ohmic contacts for MoS 2 , MoSe 2 and WSe 2 FETs. The low-resistance ohmic contacts lead to drastically improved device performance, including on/off ratios up to >10 9 , drive currents >320 µA µm -1 , and two-terminal extrinsic field-effect mobilities up to 2.8×10 3 cm 2 V -1 s -1 at cryogenic temperatures.…”

Hydrogen evolution activity of individual mono-, bi-, and few-layer MoS 2 towards photocatalysis

“…Under highest illumination intensity and at an overpotential of = −0.4 V, a current density gain of 70 mA cm −2 is observed that is almost doubled compared to the bulk value of 42 mA cm −2 . The increased photo-activity is assumed to be due to an effective separation of the photo-generated electron hole pairs by internal electric fields across the individual steps [72]. Due to the thickness-dependent band structure of MoS 2 these steps effectively function as multiple lateral heterojunctions [72] reducing the loss of the photo-generated charge carriers by radiative recombination.…”

Pronounced Photovoltaic Effect in Electrically Tunable Lateral Black‐Phosphorus Heterojunction Diode

“…[35] This difference in a heterojunction is likely to give rise to an obvious current rectification behavior. [28] As for the V g dependence, briefly, when V g has a large enough negative value, both the regions (of different layer numbers) of the device are electrostatically modulated into heavy p-type forming a p + -p + junction. Hence, no significant rectifying phenomenon is expected at the thick-thin flake interface.…”

“…[25] Such dependence implies energy bands discontinuities at the interface of different-layer-number films, forming spontaneously a lateral heterojunction distinct from the conventional ones. [26][27][28][29] The study on this kind of structure is likely to expand the realms of 2D materials diverse applications but few works have been done. [26,28,29] Recently, few-layer black phosphorus has been rediscovered as a novel promising 2D semiconductor for nextgeneration nanoelectronic and optoelectronic devices due to its direct bandgap, ambipolar conduction, anisotropic nature, and a high field-effect hole mobility.…”

“…[26][27][28][29] The study on this kind of structure is likely to expand the realms of 2D materials diverse applications but few works have been done. [26,28,29] Recently, few-layer black phosphorus has been rediscovered as a novel promising 2D semiconductor for nextgeneration nanoelectronic and optoelectronic devices due to its direct bandgap, ambipolar conduction, anisotropic nature, and a high field-effect hole mobility. [30][31][32][33] Especially, BP has a largely adjustable direct thickness-dependent bandgap ranging from 2.0 eV for monolayer to 0.3 eV for its bulk form, [34] which bridges the bandgap space between gapless graphene and large gap TMDCs by covering the mid-infrared to near-infrared wavelengths, leading to new electronic and optoelectronic devices.…”