scholarly journals Unveiling defect-mediated carrier dynamics in monolayer semiconductors by spatiotemporal microwave imaging

2020 ◽  
Vol 117 (25) ◽  
pp. 13908-13913
Author(s):  
Zhaodong Chu ◽  
Chun-Yuan Wang ◽  
Jiamin Quan ◽  
Chenhui Zhang ◽  
Chao Lei ◽  
...  
Keyword(s):  
Carrier Transport ◽  
Electrical Response ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Strongly Correlated ◽  
Trap States ◽  
Time Resolved ◽  
Metal Dichalcogenides ◽  
Microwave Signals ◽  
The Time Domain

The optoelectronic properties of atomically thin transition-metal dichalcogenides are strongly correlated with the presence of defects in the materials, which are not necessarily detrimental for certain applications. For instance, defects can lead to an enhanced photoconduction, a complicated process involving charge generation and recombination in the time domain and carrier transport in the spatial domain. Here, we report the simultaneous spatial and temporal photoconductivity imaging in two types of WS2monolayers by laser-illuminated microwave impedance microscopy. The diffusion length and carrier lifetime were directly extracted from the spatial profile and temporal relaxation of microwave signals, respectively. Time-resolved experiments indicate that the critical process for photoexcited carriers is the escape of holes from trap states, which prolongs the apparent lifetime of mobile electrons in the conduction band. As a result, counterintuitively, the long-lived photoconductivity signal is higher in chemical-vapor deposited (CVD) samples than exfoliated monolayers due to the presence of traps that inhibits recombination. Our work reveals the intrinsic time and length scales of electrical response to photoexcitation in van der Waals materials, which is essential for their applications in optoelectronic devices.

scholarly journals The Photodetectors Based on Lateral Monolayer MoS2/WS2 Heterojunctions

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Caihong Li ◽  
Juntong Zhu ◽  
Wen Du ◽  
Yixuan Huang ◽  
Hao Xu ◽  
...  
Keyword(s):  
Communication Systems ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Large Area ◽  
Optical Signals ◽  
Metal Dichalcogenides ◽  
One Step ◽  
The One ◽  
Charge Carrier Trapping ◽  
Sharp Interfaces

AbstractMonolayer transition metal dichalcogenides (TMDs) show promising potential for next-generation optoelectronics due to excellent light capturing and photodetection capabilities. Photodetectors, as important components of sensing, imaging and communication systems, are able to perceive and convert optical signals to electrical signals. Herein, the large-area and high-quality lateral monolayer MoS2/WS2 heterojunctions were synthesized via the one-step liquid-phase chemical vapor deposition approach. Systematic characterization measurements have verified good uniformity and sharp interfaces of the channel materials. As a result, the photodetectors enhanced by the photogating effect can deliver competitive performance, including responsivity of ~ 567.6 A/W and detectivity of ~ 7.17 × 1011 Jones. In addition, the 1/f noise obtained from the current power spectrum is not conductive to the development of photodetectors, which is considered as originating from charge carrier trapping/detrapping. Therefore, this work may contribute to efficient optoelectronic devices based on lateral monolayer TMD heterostructures.

Nanoscale Characterization of WSe2for Opto-electronics Applications

MRS Advances ◽  
2017 ◽  
Vol 2 (60) ◽  
pp. 3715-3720 ◽  
Author(s):  
Nirmal Adhikari ◽  
Avra Bandyopadhyay ◽  
Anupama Kaul
Keyword(s):  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Absorber Layer ◽  
Band Alignment ◽  
Transport Layer ◽  
Electron Transport Layer ◽  
Kelvin Probe ◽  
Nanoscale Characterization ◽  
Efficient Charge ◽  
Metal Dichalcogenides

ABSTRACTTwo dimensional (2D) thin transition metal dichalcogenides are being widely investigated for optoelectronics applications. Here, we report on the interfacial study of WSe2with photo-absorber materials for efficient charge transport using Kelvin Probe Force Microscopy (KPFM) for solar cell applications. The WSe2in these experiments was synthesized using Chemical Vapor Deposition (CVD) with a WO3powder and Se pellets as the precursors, where the selenium was placed upstream in an Ar carrier gas within the furnace at a temperature zone of 260-270°C. For the interfacial analysis, nanoscale KPFM measurements show an average surface potential of 125 meV for the CVD synthesized WSe2flakes. KPFM measurements signify that a thin layer of WSe2can be used to suppress back recombination of carriers between the electron transport layer (ETL) and the absorber layer. A proper band alignment between ETL and absorber layer helps to increase the overall device performance, which we will elaborate upon in this work. Capacitance-voltage and capacitance-frequency measurements were measured to study the role of defects.

Controllable growth of multilayered XSe2 (X=W and Mo) for nonlinear optical and optoelectronic applications

2D Materials ◽  
2021 ◽  
Author(s):  
Kun Ye ◽  
Lixuan Liu ◽  
Liying Chen ◽  
Wenlong Li ◽  
Bochong Wang ◽  
...  
Keyword(s):  
Large Scale ◽  
Second Harmonic ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Fast Response ◽  
Peak Position ◽  
Metal Dichalcogenides ◽  
Controllable Growth ◽  
Optoelectronic Applications ◽  
Layered Transition Metal

Abstract The layered transition metal dichalcogenides (TMDs) exhibit the intriguing physical properties and potential application in novel electronic devices. However, controllable growth of multilayer TMDs remains challenging. Herein, large-scale and high-quality multilayer prototype TMDs of W(Mo)Se2 were synthesized via chemical vapor deposition. For Raman and PL measurements, 2H and 3R multilayer WSe2 crystals displayed significant layer-dependent peak position and intensity feature. Besides, different from the oscillatory relationship of SHG intensity for odd-even layer numbers in 2H-stacked multilayer WSe2, the second harmonic generation intensity of 3R-stacked ones parabolically increased with the thickness due to the absence of inversion symmetry. For device application, photodetectors based on WSe2 with increasing thickness exhibited p-type (bilayer), ambipolar (trilayer), and n-type (4 layers) semiconductor behaviors, respectively. Furthermore, photodetectors based on the as-synthesized 3R-stacked WSe2 flakes displayed an excellent responsivity (R) of 7.8×103 mA/W, high specific detectivity (Da*) of 1.7×1014 Jones, outstanding external quantum efficiency (EQE) of 8.6×102 %, and fast response time (τRise=57 ms and τFall=53 ms) under 532 nm illumination with bias voltage of Vds=5 V. Similar results have also been achieved in multilayer MoSe2 crystals. All these findings indicate great potential of 3R-stacked TMDs in two-dimensional optoelectronic applications.

scholarly journals Additive manufacturing of patterned 2D semiconductor through recyclable masked growth

2019 ◽  
Vol 116 (9) ◽  
pp. 3437-3442 ◽  
Author(s):  
Yunfan Guo ◽  
Pin-Chun Shen ◽  
Cong Su ◽  
Ang-Yu Lu ◽  
Marek Hempel ◽  
...  
Keyword(s):  
Electronic Materials ◽  
Field Effect Transistors ◽  
2D Materials ◽  
Direct Synthesis ◽  
Scale Up ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Great Promise ◽  
Substrate Engineering ◽  
Metal Dichalcogenides

The 2D van der Waals crystals have shown great promise as potential future electronic materials due to their atomically thin and smooth nature, highly tailorable electronic structure, and mass production compatibility through chemical synthesis. Electronic devices, such as field effect transistors (FETs), from these materials require patterning and fabrication into desired structures. Specifically, the scale up and future development of “2D”-based electronics will inevitably require large numbers of fabrication steps in the patterning of 2D semiconductors, such as transition metal dichalcogenides (TMDs). This is currently carried out via multiple steps of lithography, etching, and transfer. As 2D devices become more complex (e.g., numerous 2D materials, more layers, specific shapes, etc.), the patterning steps can become economically costly and time consuming. Here, we developed a method to directly synthesize a 2D semiconductor, monolayer molybdenum disulfide (MoS2), in arbitrary patterns on insulating SiO2/Si via seed-promoted chemical vapor deposition (CVD) and substrate engineering. This method shows the potential of using the prepatterned substrates as a master template for the repeated growth of monolayer MoS2 patterns. Our technique currently produces arbitrary monolayer MoS2 patterns at a spatial resolution of 2 μm with excellent homogeneity and transistor performance (room temperature electron mobility of 30 cm2 V−1 s−1 and on–off current ratio of 107). Extending this patterning method to other 2D materials can provide a facile method for the repeatable direct synthesis of 2D materials for future electronics and optoelectronics.

scholarly journals Measurement of Quantum Yields of Monolayer TMDs Using Dye-Dispersed PMMA Thin Films

Nanomaterials ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 1032 ◽  
Author(s):  
Shrawan Roy ◽  
Anir S. Sharbirin ◽  
Yongjun Lee ◽  
Won Bin Kim ◽  
Tae Soo Kim ◽  
...  
Keyword(s):  
Vapor Deposition ◽  
Rhodamine 6G ◽  
Composite Films ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Quantum Yields ◽  
Simple Protocol ◽  
Metal Dichalcogenides ◽  
Spatially Homogeneous ◽  
Reference Specimens

In general, the quantum yields (QYs) of monolayer transition metal dichalcogenides (1L-TMDs) are low, typically less than 1% in their pristine state, significantly limiting their photonic applications. Many methods have been reported to increase the QYs of 1L-TMDs; however, the technical difficulties involved in the reliable estimation of these QYs have prevented the general assessment of these methods. Herein, we demonstrate the estimation of the QYs of 1L-TMDs using a poly methyl methacrylate (PMMA) thin film embedded with rhodamine 6G (R6G) as a reference specimen for measuring the QYs of 1L-TMDs. The PMMA/R6G composite films with thicknesses of 80 and 300 nm demonstrated spatially homogeneous emissions with the incorporation of well-dispersed R6G molecules, and may, therefore, be used as ideal reference specimens for the QY measurement of 1L-TMDs. Using our reference specimens, for which the QY ranged from 5.4% to 22.2% depending on the film thickness and R6G concentrations, we measured the QYs of the exfoliated or chemical vapor deposition (CVD)-grown 1L-WS2, -MoSe2, -MoS2, and -WSe2 TMDs. The convenient procedure proposed in this study for preparing the thin reference films and the simple protocol for the QY estimation of 1L-TMDs may enable accurate comparisons of the absolute QYs between the 1L-TMD samples, thereby enabling the development of a method to improve the QY of 1L-TMDs.

Comparative Study of Photocarrier Dynamics in CVD-deposited CuWO4, CuO, and WO3 Thin Films for Photoelectrocatalysis

2020 ◽  
Vol 234 (4) ◽  
pp. 699-717
Author(s):  
James Hirst ◽  
Sönke Müller ◽  
Daniel Peeters ◽  
Alexander Sadlo ◽  
Lukas Mai ◽  
...  
Keyword(s):  
Thin Films ◽  
Carrier Mobility ◽  
Carrier Transport ◽  
Terahertz Spectroscopy ◽  
Chemical Vapor ◽  
Photoelectrochemical Cells ◽  
Time Resolved ◽  
And Diffusion ◽  
Wo3 Thin Films ◽  
Carrier Transport Properties

AbstractThe temporal evolution of photogenerated carriers in CuWO4, CuO and WO3 thin films deposited via a direct chemical vapor deposition approach was studied using time-resolved microwave conductivity and terahertz spectroscopy to obtain the photocarrier lifetime, mobility and diffusion length. The carrier transport properties of the films prepared by varying the copper-to-tungsten stoichiometry were compared and the results related to the performance of the compositions built into respective photoelectrochemical cells. Superior carrier mobility was observed for CuWO4 under frontside illumination.

scholarly journals Transition metal dichalcogenides bilayer single crystals by reverse-flow chemical vapor epitaxy

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Xiumei Zhang ◽  
Haiyan Nan ◽  
Shaoqing Xiao ◽  
Xi Wan ◽  
Xiaofeng Gu ◽  
...  
Keyword(s):  
Transition Metal ◽  
Single Crystals ◽  
Reverse Flow ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Metal Dichalcogenides

Electrical Characteristics of a Chemical Vapor Deposition-Grown MoS2 Monolayer-Based Field Effect Transistor

2020 ◽  
Vol 15 (6) ◽  
pp. 673-678
Author(s):  
Soo-Young Kang ◽  
Gil-Sung Kim ◽  
Min-Sung Kang ◽  
Won-Yong Lee ◽  
No-Won Park ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Field Effect ◽  
Field Effect Transistors ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Electrical Characteristics ◽  
Mos2 Monolayer ◽  
2D Semiconductors ◽  
Metal Dichalcogenides

Transition metal dichalcogenides (TMDs) are layered two-dimensional (2D) semiconductors and have received significant attention for their potential application in field effect transistors (FETs), owing to their inherent characteristics. Among the various reported 2D TMD materials, monolayer (ML) molybdenum disulfide (MoS2) is being considered as a promising channel material for the fabrication of future transistors with gate lengths as small as ∼1 nm. In this work, we present chemical vapor deposition-grown triangular ML MoS2 with a lateral size of ∼22 μm and surface coverage of ∼47%, as well as a PMMA-based wet transfer process for depositing the as-grown triangular ML MoS2 flakes onto a SiO2 (∼100 nm)/p++-Si substrate. Additionally, we demonstrate the fabrication of an n-type MoS2-based FET device and study its electrical characteristics as a function of the gate voltage. Our FET device shows an excellent on/off ratio of ∼106, an off-state leakage current of less than 10– 12 A, and a field effect mobility of ∼10.4 cm2/Vs at 300 K.

scholarly journals Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 173
Author(s):  
Der-Yuh Lin ◽  
Yu-Tai Shih ◽  
Wei-Chan Tseng ◽  
Chia-Feng Lin ◽  
Hone-Zern Chen
Keyword(s):  
Electron Microscopy ◽  
Activation Energy ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Vital Role ◽  
Chemical Vapor Transport ◽  
Time Resolved ◽  
Cu Doping ◽  
Photoelectric Properties ◽  
Co Doped

Doping plays a vital role in the application of transition-metal dichalcogenides (TMDCs) because it can increase the functionality of TMDCs by tuning their native characteristics. In this study, the influence of Mn, Fe, Co, and Cu doping on the photoelectric properties of HfS2 was investigated. Pristine, Mn-, Fe-, Co-, and Cu-doped HfS2 crystals were grown using the chemical vapor transport method. Scanning electron microscopy images showed that the crystals were layered and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy measurements confirmed that the crystals were in the 1T-phase with a CdI2-like structure. The bandgap of pristine HfS2 obtained from the absorption and photoconductivity spectra was approximately 1.99 eV. As the dopant changed from Mn, Fe, and Co, to Cu, the bandgap gradually increased. The activation energies of the samples were determined using temperature-dependent current-voltage curves. After doping, the activation energy decreased, and the Co-doped HfS2 exhibited the smallest activation energy. Time-resolved photoresponse measurements showed that doping improved the response of HfS2 to light; the Co-doped HfS2 exhibited the best response. The photoresponsivity of HfS2 as a function of the laser power and bias voltage was measured. After doping, the photoresponsivity increased markedly; the Co-doped HfS2 exhibited the highest photoresponsivity. All the experimental results indicated that doping with Mn, Fe, Co, and Cu significantly improved the photoresponsive performance of HfS2, of which Co-doped HfS2 had the best performance.

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