Browsing by Author "Pandey, S.K."

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A DFT study of the adsorption behavior and sensing properties of CO gas on monolayer MoSe2 in CO2-rich environment
(Springer Science and Business Media Deutschland GmbH, 2024) Vinturaj, V.; Yadav, A.K.; Singh, R.; Garg, V.; Bhardwaj, R.; Ajith, K.M.; Pandey, S.K.
Context: Carbon monoxide, also known as the “silent killer,” is a colorless, odorless, tasteless, and non-irritable gas that, when inhaled, enters the bloodstream and lungs, binds with the hemoglobin, and blocks oxygen from reaching tissues and cells. In this work, the monolayer MoSe2-based CO gas sensors were designed using density functional theory calculation with several dopants including Al, Au, Pd, Ni, Cu, and P. Here, Cu and P were found to be the best dopants, with adsorption energies of −0.67 eV (Cu) and −0.54 eV (P) and recovery times of 1.66 s and 13.8 ms respectively. Cu conductivity for CO adsorption was found to be 2.74 times that of CO2 adsorption in the 1.0–2.26 eV range. P displayed the highest selectivity, followed by Pd and Ni. The dopants, Pd and Ni, were found suitable for building CO gas scavengers due to their high recovery times of 9.76 × 1020 s and 2.47 × 1011 s. Similarly, the adsorption of CO2 on doped monolayer MoSe2 was also investigated. In this study, it is found that monolayer MoSe2 could be employed to create high-performance CO sensors in a CO2-rich environment. Method: The electrical characteristics of all doped MoSe2 monolayers are obtained using a DFT calculation with the PBE-GGA method from the Quantum ESPRESSO package. The self-consistent field (SCF) computations were performed using a 7 × 7 × 1 k-point grid and a norm-conserving pseudo potential (NCPP) file. To determine electrical conductivity, the semi-classical version of Boltzmann transport theory, implemented in the Boltz Trap code, was used. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Accident Prediction Model for Horizontal Curves on State Highways Using Spatial Variation
(Springer Science and Business Media Deutschland GmbH, 2025) Pandey, S.K.; Mulangi, R.H.; Sanganaikar, R.S.; Babu, K.R.N.N.
Accidents have become one of the primary cause of fatalities on highways. Road accidents are one of the significant issue around the globe, but in context of India, the severity is more due to immense growth in road networks and traffic capacity. Curve are at higher range of potential risks of accidents because of inadequate sight distance and speed measures. This study aims to develop accident prediction model using regression analysis. Location selected for study was State Highway-1 in Udupi district, Karnataka. Ten curves are selected on the road and comparative study of model prepared is checked to verify the model reliability. Datasets used for model calibration and development is Highway Geometric data, past accidents records, and spot speed of vehicles. Geometric data for the road sections are obtained from satellite imageries, and GIS data and speed data are collected using speed camera. Model generation was done using statistical computing by using multi-linear regression. The model showed that curve details and speed reduction between successive features were strongly related to accident frequency. Sharper curves are more tend to accidents, and speed reduction is higher at curves with smaller radius. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Comprehensive Modeling of High-Performance All-Inorganic Cs2TiBr6-Based Perovskite Solar Cells
(John Wiley and Sons Inc, 2024) Kumar, S.; Thiyyakkandy, J.; Yadav, A.K.; Vinturaj, V.; Garg, V.; Prabhu, S.; Pandey, S.K.
The perovskites are desirable materials for photovoltaic and other renewable green energy technologies. Lead-based perovskite solar cells (PSC) have recently gained considerable attention due to the abrupt rise in power conversion efficiency, but lead's well-known toxicity prevents its large-scale commercialization. One compelling option is Cs2TiBr6, which offers a nontoxic alternative. Herein, the electronic and optical characteristics of Cs2TiBr6 absorber material using density functional theory employing the WIEN2K tool are investigated. The energy band structure of Cs2TiBr6 shows an indirect bandgap of 2.2 eV. Additionally, optical properties are calculated, and the suitability of this material as an absorber for indoor and outdoor photovoltaic devices is investigated. The Cs2TiBr6 material has a peak absorption coefficient of 39.57 × 104 cm−1 and optical conductivity of 1.98 × 1015s−1, demonstrating its suitability as an absorber material. After that, a PSC is modeled using SCAPS-1D by using the computed parameters. The performance of the modeled perovskite is enhanced by optimization of various parameters, resulting in the achievement of a high-performance Cs2TiBr6-based PSC, boasting a power conversion efficiency of 19.9% for air mass AM1.5 G spectra and power conversion efficiency of 16.76% for light emitting diode and 17.18% for incandescent light for indoor light conditions. © 2024 Wiley-VCH GmbH.
Design and fabrication of all-inorganic transport materials-based Cs2SnI6 perovskite solar cells
(Springer, 2023) Kumari, D.; Jaiswal, N.; Shukla, R.; Punetha, D.; Pandey, S.K.; Pandey, S.K.
With lead-based perovskite materials, lead content and long-term stability are the big concerns. Recently, Cesium tin iodide (Cs2SnI6) double perovskite has gained recognition as a stable and environment-friendly photovoltaic material compared to lead-based perovskite materials. In the present study, we have investigated Cs2SnI6 based solar cell with all inorganic transport materials using SCAPS-1D. The optimized device exhibited a maximum efficiency of about 18%. Further we fabricated Cs2SnI6 perovskite films using a solution process approach, utilizing CsI and SnI4 in a 2:1 ratio. For synthesized double perovskite film, the crystallinity, morphologies, and optical characteristics were examined. Additionally, the stability analysis confirmed that the prepared perovskite films were stable for more than two months under ambient exposure. Finally, utilizing the synthesized Cs2SnI6 thin films as an absorber material, we fabricated two solar cells without and with hole transport layer (HTL), having configurations of glass/FTO/ZnO/Cs2SnI6/Ni and glass/FTO/ZnO/Cs2SnI6/ MoS2/Ni, respectively, in the ambient conditions. As a major finding, it has been observed that the inclusion of MoS2 as HTL improved overall performance, with an enhancement in the power conversion efficiency (PCE) of nearly 45% compared to the device without HTL. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Detection of acceptor-bound exciton peak at 300 K in boron–phosphorus co-doped ZnMgO thin films for room-temperature optoelectronics applications
(Elsevier B.V., 2021) Sushama, S.; Murkute, P.; Ghadi, H.; Pandey, S.K.; Chakrabarti, S.
It is well-known that the ZnMgO thin-film faces a roadblock in its potential applications for various optoelectronic devices due to the limitation imposed on achieving p-type conduction. The mono-acceptor doping of ZnMgO endures from the stern self-compensation by native donor defects and deep acceptor level formation advocating the need for alternate doping techniques like co-doping. In this paper, we report a detailed study on the improvement in structural, elemental, and optical properties of phosphorus-doped Zn0.85Mg0.15O thin films, with an aim to obtain enhancement in the signatures of acceptor-doped behavior, under the influence of boron implantation time. In addition, the paper also captures the behavior exhibited by the co-doped samples as a result of the variation in the annealing temperature. The solubility of the phosphorus atom (acceptor dopant) was observed to improve with boron (donor co-dopant) implantation as confirmed by the structural, elemental, and optical properties of co-doped ZnMgO thin films. It was also found that the acceptor level emissions got improved after boron implantation in phosphorus-doped ZnMgO thin films. Additionally, with co-doping, the sample showed the signature of acceptor-bound exciton peak till 300 K, evidencing the room-temperature operability of the films. Moreover, the fabricated film had a shallow acceptor energy level located at around 74 ± 0.45 meV above the valence band. Co-doped samples also showed stable acceptor based optical emission for more than a year. © 2020 Elsevier B.V.
DFT Calculations for Temperature Stable Quantum Capacitance of VS2 Based Electrodes for Supercapacitors
(Institute of Electrical and Electronics Engineers Inc., 2024) Yadav, A.K.; Shreevathsa, N.S.; Singh, R.; Das, P.P.; Garg, V.; Pandey, S.K.
Using density functional theory calculations, we demonstrate the quantum capacitance of the VS2 electrode which can be improved by doping with non-metallic elements such as nitrogen (N), phosphorus (P), and arsenic (As) atoms. The radius, charge, and morphology of these non-metallic elements help to improve the performance of VS2 material as electrodes of supercapacitors. The As-doped VS2 monolayer demonstrated the maximum quantum capacitance of 31.2369 μF/cm2 at 300 K. At 1200 K, quantum capacitance reaches the value of 25.2149 μF/cm2, showing the inconsiderable change in value for this wide range of temperature variation. Additionally, the other important properties of undoped and doped VS2 monolayers such as density of states, energy band structure, electrical conductivity, thermal conductivity, and the Seebeck coefficient were also computed and examined in detail. The band structure of the P and As-doped VS2 monolayers showed a metallic nature, which is suitable for electrode application. In the case of As-doped VS2 material, a high figure of merit of 3.536 was observed by using DFT-D2 calculations, due to the large Seebeck coefficient and significant electrical conductivity. Our findings will be helpful in further exploring the suitability of VS2 monolayers as electrodes of supercapacitors. © 2002-2012 IEEE.
DFT Study about the Effect of Doping on the Properties of GaSb Material and Designing of High-Efficiency Infrared Photodetector
(John Wiley and Sons Inc, 2023) Bhandari, B.; Yadav, A.K.; Singh, R.; Kiran, G.; Singh, A.K.; Garg, V.; Pandey, S.K.
The gallium antimonide (GaSb) material has very attractive electronic and optoelectronic properties which are suitable for next-generation infrared (IR) photodetector applications. In this work, properties of undoped GaSb material such as density of states, bandstructure, electron density, absorption coefficient, dielectric function, refractive index, and extinction coefficient are calculated using density-functional theory (DFT). Moreover, the effects of doping with Ge, Sn, and Zn elements on these properties of GaSb material are investigated. It is found that undoped GaSb material exhibits a direct gap of ≈0.72 eV. Among different doping elements, Ge-doped GaSb produces a very significant enhancement in optical properties. The Ge-doped GaSb demonstrates a four times higher absorption coefficient in comparison to undoped GaSb in the IR region at 0.8 eV photon energy. GaSb-based photodetector device is designed using the Solar Cell Capacitance Simulator (SCAPS) 1D tool. The efficiency of the designed photodetector with optimum thicknesses and doping of different layers is found to be improved from 21.34% to 25.91% after incorporating the absorption data set obtained from the DFT calculations. Additionally, the photodetector with optimum parameters demonstrates maximum responsivity of value ≈0.31 A W−1. In the previous findings, it is demonstrated that GaSb is a very suitable material for next-generation IR photodetector applications. © 2023 Wiley-VCH GmbH.
Doping of ZnMgO with phosphorus by spin-on dopant technique
(SPIE, 2021) Mishra, M.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.
Zinc magnesium oxide is a ternary compound wide bandgap semiconductor. Incorporation of Mg into ZnO helps in increasing the of p-type conductivity by affecting the background n-type nature of ZnO. This is possible because Mg incorporation in ZnO elevates the conduction band edge which in turn increases the distance between the shallow donor level and conduction band minima, resulting increase of activation energy for background donor. In this work, we report Spin-on Dopant technique to dope phosphorus in Zn0.85Mg0.15O lattice. The undoped ZnMgO thin film (sample A) was deposited using RF sputtering. The SOD sample (sample B) was prepared using P509 spin on dopant and kept approximate 1cm above ZnMgO film at 600Â°C for four hours. The doped sample was annealed at temperature 700Â°C (sample C) in oxygen ambient to see the high temperature annealing effect on doping. In studies of high-resolution x-ray diffraction, a dominant (002) peak was observed in sample A, B, and C at 34.173Â°, 34.624Â°, and 34.638Â° respectively. The shifting of (002) peak at higher angle for doped samples indicates the phosphorus doping in film. The XPS spectra of phosphorus 2p peak are appears at âˆ¼134 eV indicates the presence of P atoms as P-O bonds in ZnMgO lattice. The Donor-Acceptor pair (DAP) transition peak around 3.473eV and free Acceptor (AXÂ°) peak around 3.588eV were found in photoluminescence spectra of sample B revels the phosphorus doping in ZnMgO. Â© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
Dual oxygen reservoir model for nonpolar resistive switching in nickel tetradecavanadate based molecular switch
(Elsevier B.V., 2025) Thathron, N.; Biradar, B.R.; Pandey, S.K.; Mal, S.S.; Das, P.P.
The data explosion and computing limitations of traditional computer systems have led researchers to find alternate data storage devices. Resistive random access memory devices have been accepted as a promising candidate to meet the growing demand for multi-bit memory storage and unconventional computing applications. In this report, we provide a comprehensive mechanistic insight into the multistate nonpolar resistive switching in nickel-embedded polyoxovanadate molecules, K2H5[NiV14O40] based memory device having the architecture Al/K2H5[NiV14O40]/ITO. Such molecular cluster belongs to a larger group of polyoxometalate family. The formation and rupture of multiple conductive filaments made up of oxygen vacancies and their lateral widening with different compliance currents allow the device to exhibit multiple resistance states. The resistance states are likely to be modulated by the multiple redox reactions of Ni and V centers of the active switching layer. The coexistence of two unipolar and two bipolar modes of resistive switching suggests that the device can be modeled as having a dual oxygen reservoir structure where both thermochemical and electrochemical mechanisms of filament theory for resistive switching coexist in the same memory cell. The observation of quantized steps in the conductance plot confirms the conductive filament based resistive switching. The enhancement and reduction in conductance with the increase in the number of pulses can mimic the potentiation and depression in biological synapses. This promises that the polyoxometalate based resistive switching devices can connect memory with neuromorphic applications. © 2025 Elsevier B.V.
Effect of Introducing Defects and Doping on Different Properties of Monolayer MoS2
(John Wiley and Sons Inc, 2023) Prajakta, K.; Vinturaj, V.P.; Singh, R.; Garg, V.; Pandey, S.K.; Pandey, S.K.
Herein, the comprehensive study of different properties of undoped MoS2, MoS2 lattice with sulfur (S) and, molybdenum (Mo) vacancy, and MoS2 with substitutional doping of niobium (Nb), vanadium (V), and zinc (Zn) atoms is done. The density functional theory (DFT) is used and the electronic properties like density of states, band structure, electron density, and optical properties like dielectric function, optical conductivity, and refractive index are studied. It is observed that undoped MoS2 monolayer shows direct bandgap semiconductor characteristics with a bandgap of around 1.79 eV. P-type characteristics are observed for Nb-, V-, and Zn-doped MoS2 lattices. The real part and imaginary parts of all optical parameters along x and z directions for different MoS2 supercells are found to be anisotropic in nature up to a photon energy of almost 11 eV and thereafter they show nearly isotropic nature. Finally, it is found that the obtained properties of MoS2 monolayer as per literature are suitable for next-generation MOSFET application. © 2023 Wiley-VCH GmbH.
Effect of post-deposition annealing ambient on Gallium Oxide (Ga2O3) films
(SPIE, 2022) Mishra, M.; Saha, R.; Bhowmick, S.; Pandey, S.K.; Chakrabarti, S.
Gallium Oxide (Ga2O3) is an emerging wideband semiconductor which can be utilize in solar-blind photodetector and high power electronics application. Having a large bandgap and high breakdown field makes Ga2O3 material suitable for these device applications. However, the physical and the optical properties of Ga2O3 can be tailored by changing the annealing ambient and temperature, and understanding how the annealing atmosphere can affect these properties is crucial for designing a next generation optoelectronic devices. Moreover, the presence of defects and impurities can also affect the device parameters. Thus, in this work, we have investigated the influence of post deposition annealing atmosphere on the morphological, structural, and optical properties of Ga2O3 films. The prepared samples were further went through thermal annealing at 800â„ƒ for 30 mins in Nitrogen (N2), and Oxygen (O2) ambient to achieve Î²-phase of Ga2O3. The structural properties of all the samples were studied by Atomic force microscopy, and X-ray diffraction while the optical properties were studies by UV-Visible, and photoluminescence spectroscopy. We have found monoclinic Î²-phase in the polycrystalline annealed Ga2O3 samples. The optical band gap of films were increased after annealing and highest band gap is obtained to 5.44eV in N2 annealed sample as compared to as-deposited sample (4.56eV). A broad photoluminescence spectrum ranged from 350 to 480 nm was observed, which further deconvoluted in three peaks at around 378 nm, 399 nm, and 422 nm in as-deposited sample. The same peaks with broad photoluminescence spectrum was found to be blue shifted for annealed samples as compared to the as-deposited. This study will open a new direction in future deep-UV photodetector fabrication. Â© 2022 SPIE.
Enhancement in structural, elemental and optical properties of boron–phosphorus Co-doped ZnO thin films by high-temperature annealing
(Elsevier B.V., 2021) Sushama, S.; Murkute, P.; Ghadi, H.; Pandey, S.K.; Chakrabarti, S.
The inherent n-type nature of zinc oxide (ZnO) and its unstable p-type behavior with single dopant species have encouraged researchers to explore the effect of multiple dopants as a viable solution for long-term stability and repeatability. Herein, we report boron (B) and phosphorus (P) co-doped ZnO thin films engineered through an optimized ion implantation technique followed by annealing at 1000 °C in oxygen ambiance. We investigated their structural, chemical, and optical properties to capture the effect of both boron implantation duration and annealing temperature. Co-doping with boron was observed to boost phosphorus incorporation in the film. Compared with P-doping, P–B co-doping increased the dominance of acceptor-bound exciton peak and also, suppressed non-radiative/visible emission which is due to reduced Madelung energy. After high-temperature annealing at 1000 °C, further narrowing of optical emission peaks generated due to acceptor incorporation was observed. Also, the co-doped samples showed stability in the acceptor behavior for more than one year. © 2021 Elsevier B.V.
Enhancement of Functionalized 1T-NbS2 Monolayer Properties for the Superior Anode of Na-Ion Batteries
(Institute of Electrical and Electronics Engineers Inc., 2025) Jasil, T.K.; Yadav, A.K.; Maurya, G.K.; Garg, V.; Pandey, S.K.
One of the most important factors influencing the performance of Na-ion batteries (NIBs) is the anode’s quality. Currently, NIB anodes have numerous disadvantages, including low capacity, rapid volume change, temperature variable conductivity and poor thermal/chemical stability. In this work, the electronic and transport properties of undoped, doped and defective 1T-NbS2 monolayers were investigated using density functional theory calculations. The maximum quantum capacitance of 1T-NbS2 with S-vacancy (VS-NbS2) changes from 20.49 to 16.92 ?F/cm2 across temperature ranges of 200 K to 1000 K, indicating its suitability as anode with temperature-stable capacity. The 1T-NbS2 monolayers exhibit high electrical conductivity with less than 6% fluctuation across a temperature range of 200 K to 1000 K, indicating thermally stable conductance. The 1T-NbS2 layered structure has substantially larger interlayer spacing of 0.615 nm than the size of Na ion (0.095 nm), as well as a relatively tiny variation (0.05 eV for VS-NbS2) in cohesive energies between sodiated and de-sodiated phases, making it a good choice for anodes. For VS-NbS2, the seebeck coefficient ranges from -5 to -40 ?V/K, which is often obtained by the most commonly used Na-metal anode, demonstrating its appropriateness as anode. According to our findings, 1T-NbS2 is a great option for thermally stable NIB electrode applications. © 2002-2012 IEEE.
Experimental investigation and comparative analysis of electron beam evaporated ZnO/MgxZn1-xO/CdxZn1-xO thin films for photodiode applications
(Academic Press, 2021) Kumar, R.R.; Shukla, R.; Pandey, S.K.; Pandey, S.K.
— This work reports the growth optimization and analysis of ZnO, MgxZn1-xO, and CdxZn1-xO thin films on silicon substrate using an electron beam evaporation system. The crystal phase purity, surface morphology, optical and electrical properties of deposited ZnO, MgxZn1-xO, and CdxZn1-xO thin films were studied. X-ray diffraction (XRD) spectra revealed that the deposited films were polycrystalline in nature with preferred (002) crystal orientation. Field emission scanning electron microscope study showed a dense-packed grained structure with an exact symmetrical distribution. The root-mean-square roughness of 3.03 nm was perceived by atomic force microscopy measurement for MgxZn1-xO thin-film, indicating good morphology of the deposited film. Photoluminescence measurement demonstrated a near-band-edge emission peak around 363 nm for ZnO thin film. The energy band gap obtained for ZnO, MgxZn1-xO, and CdxZn1-xO were 3.36 eV, 3.86 eV, and 2.89 eV, respectively, as measured by Ultraviolet–Visible spectroscopy. The higher amount of photocurrent was detected in illumination condition compared to dark condition with responsivity 0.54 AW-1 for ZnO films, making it suitable for photodiodes applications. © 2020 Elsevier Ltd
Fabrication of 1T VS2 Electrode-Based In-Plane Micro-Supercapacitor Using a Cost-Effective Mask-Assisted Printing Technique
(John Wiley and Sons Inc, 2023) Mandal, A.; Yadav, A.K.; Pandey, S.K.; Chakrabarti, S.
Vanadium disulfide (VS2) is an important member of the transition-metal dichalcogenides (TMDs) family, which offers high conductivity. In nature, it can exist in two phases, i.e., 1T and 2H. Herein, the metallic 1T VS2-based in-plane micro-supercapacitor (MSC) is fabricated by a facile-mask-assisted printing technique. Initially, the 1T VS2 nanosheets are synthesized using a simple one-pot hydrothermal route. The material characterizations have claimed the formation of a 1T phase and the density of states (DOS) reveal that the 1T phase of VS2 is metallic in nature. After experimental and theoretical investigations of synthesized nanosheets, a VS2 electrode-based in-plane MSC is fabricated using a simple mask-assisted printing technique. The fabricated device demonstrates excellent capacitance retention of 97.6% after 1000 cycles of cyclic voltammetry measurement at a 100 mV s−1 scan rate. The device also shows an excellent areal capacitance of 212.7 mF cm−2 and a high areal energy density of 10.63 μWh cm−2 at a high-power density of 4.45 mW cm−2. This low-cost and simple fabrication process can produce high-performance in-plane MSC devices. © 2023 Wiley-VCH GmbH.
Facile hydrothermal synthesis of vanadium disulfide nanomaterial for supercapacitor application
(SPIE, 2023) Mandal, A.; Pandey, N.; Pandey, S.K.; Yadav, A.K.; Chakrabarti, S.
Vanadium disulfide (VS2) is a prominent metallic member of transition metal dichalcogenides (TMDs) family and has already demonstrated its flair in energy storage device applications such as supercapacitors and batteries. In this work, we have synthesized hexagonal shape VS2 nanomaterial using a facile one step hydrothermal route and investigated the phase, morphology and structural properties of the material. The formation of phase has been confirmed from the X-ray diffraction (XRD) plot by correlating with the database of Joint Committee on Powder Diffraction Standards (JCPDS) 00-036-1139 of 1T VS2. Further, the crystalline behavior of VS2 nanomaterial can be seen from the high resolution transmission electron microscopy (HRTEM) measurement. Moreover, the morphology of the synthesized material is obtained from the field emission gun-scanning electron microscopy (FEG-SEM). Also, the characteristic Raman peaks of 1T VS2 at 140.3 cm-1 and 192.3 cm-1 have been observed from the Raman spectrum indicating the metallic behavior of synthesized material. The peak at 281.8 cm-1 is attributed to the in-plane vibrational mode (E2g1) while the peak at 404.5 cm-1 represents the out-of-plane vibrational mode (A1g) of V-S bond. The Fourier transform infrared (FTIR) spectrum shows the V-S-V and V=S vibrational modes around 534 cm-1 and 982 cm-1 respectively. The study introduces a low cost, large scale, highly crystalline, and metallic VS2 nanomaterial with potential application for next generation supercapacitors and other energy storage devices. Â© 2023 SPIE.
Growth of Very Large MoS2Single Crystals Using Out-Diffusion Transport and Their Use in Field Effect Transistors
(Institute of Electrical and Electronics Engineers Inc., 2021) Pandey, S.K.; Izquierdo, N.; Campbell, S.
Monolayer molybdenum disulfide (MoS2) is an attractive 2D material with a wide range of potential applications in the field of electronics and optoelectronics. To obtain the best performance, it is very necessary to grow large area single crystals of MoS2 (single domain) to avoid the effects of grain boundaries, but is exceptionally challenging to do this. Here, we report a novel method which we call out-diffusion vapor transport to grow large area single crystal monolayer MoS2 using an otherwise conventional chemical vapor deposition system. In this method, microchannels were created on the boat to significantly limit the region where MoOx vapor can react with S vapor to form crystals. This growth method resulted in triangular monolayer MoS2 single crystals up to ?640 ?m on a side grown on an oxidized silicon substrate, the largest crystals reported to date. Most of these crystals were multilayer at the center. This common feature has been identified in the literature as partially reduced transition metal oxide nucleates a second layer. We also achieved fully monolayer MoS2 single crystals up to ?450 ?m on a side, the largest demonstrated without the MoOx. Fabricated field effect transistors (FET) using MoS2 monolayer crystal as the active layer demonstrate a conventional n-type behavior, room-temperature mobility up to 45.5 cm2 V-1 s-1 and a maximum ON-Current (ION)/OFF-current (IOFF) ratio of 1.8 × 107. Raman and Photoluminescence results indicate that the as-grown large area monolayer crystals have high crystalline quality and uniformity with minimal defects, a finding that is consistent with the high electron mobility. This research work provides a superior technique to grow large-area high-quality single-crystal monolayer MoS2 without resorting to exotic equipment or techniques. © 2002-2012 IEEE.
Growth optimization and DFT investigation of doping effect on properties of VS2 monolayer crystals
(Springer Science and Business Media Deutschland GmbH, 2023) Yadav, A.K.; Patel, C.; Kiran, G.; Singh, R.; Singh, A.K.; Garg, V.; Mukherjee, S.; Pandey, S.K.
The vanadium disulfide (VS2) material, a prominent member of the two-dimensional materials family, has great potential to bridge the performance gap between current performance and contemporary energy storage device needs. Here, we report the optimization of the growth temperature of VS2 monolayer crystals using a chemical vapor deposition system. It is also found the crystal size increases with the increase of growth temperature up to 770 °C. Further increasing of growth temperature resulted in a reduction of crystal size. The atomic force microscopy measurement demonstrated the growth of monolayer thick VS2 crystal. Raman spectra revealed the formation of H-phase monolayer high-quality VS2 crystals. To understand the precise impact of doping on electronic properties, the substitutional doping of VS2 monolayer with chromium, molybdenum, and tungsten was also examined using density functional theory. The VS2 monolayer exhibits an indirect energy band gap that decreases after chromium doping of the VS2 lattice and vanishes after molybdenum and tungsten doping. Finally, it is found that tungsten-doped VS2 monolayer exhibits strong metallic character and other exceptional properties, making it suitable for electrodes of various energy storage devices. Graphical abstract: [Figure not available: see fulltext.]. © 2023, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.
Improvement in optical and elemental properties of spin-on phosphorus doped ZnO film
(SPIE, 2021) Mishra, M.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.
SOD is a type of conventional doping technique where diffusion of dopant atom takes place from the liquid source to film by thermal annealing of sample. The study shows the SOD process is a cost effective, less destructive and an efficient way to dope ZnO film. We have doped ZnO films with phosphorus atom by simply annealing it in atmospheric furnace up to 600Â°C for 4 hrs. After in-situ annealing SOD process, sample has also been ex-situ annealed at 900Â°C in oxygen ambient for 10 secs. The elemental analysis of phosphorus 2p peak at 132.62 eV ensures the existence of P-O bond for doped sample which shows phosphorus replacing Zn and bonding with oxygen in to the lattice in order to make Pzn-2Vzn an acceptor complex. The doped samples showed the photoluminescence peak at 3.32eV and 3.35eV, which attributed to free electron to acceptor (FA) and acceptor-bound exciton (A0X) energy as an evidence of acceptor doping in ZnO film. The ex-situ annealing of doped sample further improves in passivation of deep level defects of film. All sample has (002) orientation, and a compressive stress to be found in the doped sample due to phosphorus replacing Zn, are confirmed by analysis of XRD results. Â© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
Improvement in performance of CZTSSe solar cell by using cadmium free buffer layers
(SPIE, 2021) Prabhu, S.; Pandey, S.K.; Chakrabarti, S.
Cadmium Sulphide(CdS) has been the most preferred n-type buffer layer and Indium Tin Oxide(ITO) is the popular window layer in kesterite solar cells. Cadmium being toxic and Indium being a rare earth element, continuous efforts are being made to replace these materials from kesterite solar cells structure. In this work, ZnS, ZnSe, and Zn0.8Sn0.2O are considered as possible alternatives for CdS. Similarly, Aluminium doped Zinc Oxide(AZO) is considered as an alternative for ITO. Firstly, a cell model with CdS and ITO (Mo/CZTSSe/CdS/ZnO/ITO) is developed using SCAPS-1D software. To optimise the performance parameters namely open-circuit voltage(Voc), short-circuit current density(Jsc), fill factor(FF), and the power conversion efficiency (PCE) for irradiation under normal working conditions, thickness and the composition ratio of the absorber layer(CZTSSe) are evaluated through numerical simulations. PCE of 14.51% is achieved for a 40% of Sulphur content and 2 um thickness of Cu2ZnSn(SxSe1-x)4 when CdS is used as the buffer layer. For the same structure, replacing ITO with AZO results in a PCE of 14.62%. Use of Cadmium-free buffer layers ZnS, ZnSe, and Zn0.82Sn0.18O with ITO as window layer result in PCE of 13.98%, 14.28%, and 14.53%, respectively. For the Cadmium-free buffer layers, an improvement in PCE is achieved when ITO is replaced by AZO, with the highest being 14.62% for Zn0.82Sn0.18O. This can be attributed to the smaller conduction band offset, which reduces the recombination of photogenerated carriers and improves the carrier transport in the solar cell. The above results indicate that the Zn0.8Sn0.2O and AZO can be potential candidates for the buffer layer and window layer, respectively, for high-performance and cheap kesterite solar cells. Â© 2021 SPIE.