Photoresponse of atomically thin MoS2 layers and their planar heterojunctions

Abstract

MoS2 monolayers exhibit excellent light absorption and large thermoelectric power, which are, however, accompanied with very strong exciton binding energy - resulting in complex photoresponse characteristics. We study the electrical response to scanning photo-excitation on MoS2 monolayer (1L) and bilayer (2L) devices, and also on monolayer/bilayer (1L/2L) planar heterojunction and monolayer/few-layer/multi-layer (1L/FL/ML) planar double heterojunction devices to unveil the intrinsic mechanisms responsible for photocurrent generation in these materials and junctions. Strong photoresponse modulation is obtained by scanning the position of the laser spot, as a consequence of controlling the relative dominance of a number of layer dependent properties, including (i) photoelectric effect (PE), (ii) photothermoelectric effect (PTE), (iii) excitonic effect, (iv) hot photo-electron injection from metal, and (v) carrier recombination. The monolayer and bilayer devices show peak photoresponse when the laser is focused at the source junction, while the peak position shifts to the monolayer/multi-layer junction in the heterostructure devices. The photoresponse is found to be dependent on the incoming light polarization when the source junction is illuminated, although the polarization sensitivity drastically reduces at the monolayer/multi-layer heterojunction. Finally, we investigate laser position dependent transient response of photocurrent to reveal trapping of carriers in SiO2 at the source junction is the critical factor to determine the transient response in 2D photodetectors, and also show that, by systematic device design, such trapping can be avoided in the heterojunction devices, resulting in fast transient response. The insights obtained will play an important role in designing fast 2D TMDs based photodetector and related optoelectronic and thermoelectric devices.

arXiv commentNanoscale, 2016

References in corpus (18)

• Atomically thin MoS2: A new direct-gap semiconductor
• Anomalous Lattice Vibrations of Single and Few-Layer MoS2
• Single-Layer MoS2 Phototransistors
• Atomically thin p-n junctions with van der Waals heterointerfaces
• Ultrafast Charge Transfer in Atomically Thin MoS2/WS2 Heterostructures
• Optoelectronics with electrically tunable PN diodes in a monolayer dichalcogenide
• Solar-energy conversion and light emission in an atomic monolayer p-n diode
• The Nature of Electronic States in Atomically Thin MoS2 Field-Effect Transistors
• Chloride Molecular Doping Technique on 2D Materials: WS2 and MoS2
• Mechanisms of photoconductivity in atomically thin MoS2
• Large and tunable photo-thermoelectric effect in single-layer MoS2
• Photo-Thermoelectric Effect at a Graphene Interface Junction
• Light Generation and Harvesting in a Van der Waals Heterostructure
• Electronic and Thermoelectric Properties of Few-Layer Transition Metal Dichalcogenides
• High Thermoelectric Powerfactor in Single and Few-Layer MoS${}_2$
• Ultrafast and spatially resolved studies of charge carriers in atomically-thin molybdenum disulfide
• Elucidating the photoresponse of ultrathin MoS2 field-effect transistors by scanning photocurrent microscopy
• Investigation of Band-Offsets at Monolayer-Multilayer MoS2 Junctions by Scanning Photocurrent Microscopy

Cited by in corpus (7)

• Atomically thin p-n junctions based on two-dimensional materials
• Nature of carrier injection in metal/2D semiconductor interface and its implications to the limits of contact resistance
• Photodetectors based on junctions of Two-Dimensional Transition metal dichalcogenides
• Photothermoelectric effects and large photovoltages in plasmonic Au nanowires with nanogaps
• Self-Powered, Highly Sensitive, High Speed Photodetection Using ITO/WSe2/SnSe2 Vertical Heterojunction
• Asymmetrically Encapsulated vertical ITO/MoS2/Cu2O photodetector with ultra-high sensitivity
• Substrate effects in high gain, low operating voltage SnSe2 photoconductor