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Item Recent advancements in growth and stability of phosphorene: Prospects for high-performance devices(CRC Press, 2022) Pandey, S.K.; Garg, V.; Izquierdo, N.; Kumar, A.Atomically thin two-dimensional (2D) materials like graphene and the transition metal dichalcogenides have made a significant impact in the field of electronics and optoelectronics devices. Graphene, however, has no bandgap, which creates hurdles for many device applications. Similarly, the modest carrier mobility of transition metal dichalcogenides makes them less suitable for high-performance electronic and optoelectronic device applications. Phosphorene, a monolayer or few-layer form of black phosphorus (BP), has attracted considerable interest owing to its unique anisotropic manner, layer-dependent direct bandgaps, high carrier mobility, and quasi-one-dimensional excitonic nature, which are not present in other abovementioned 2D materials. Phosphorene has a bandgap of ˜0.3 eV in the bulk form and can be increased with reducing layer thicknesses, approaching ˜2 eV for the monolayer. As a result, there have been stimulating reports on field-effect transistors and inverters fabricated in the material system. Phosphorene is also becoming an interesting material for solar cells and photodetectors. Despite novel properties, the development of this material itself remains in an embryonic state. One of the reasons for the slow progress is that phosphorene-based devices use either mechanical or liquid exfoliation method to deposit phosphorene from crystalline black phosphorus (c-BP). In these processes, one peels a thin layer of material from a bulk BP crystal using adhesive tape or by liquid intercalation. The exfoliation process for this material is possible due to its intralayer strong covalent bonds and interlayer weak van der Waals forces. The exfoliation method does not have the thickness, uniformity, position, orientation, and surface control needed to get repeatable experimental results. In this chapter, detailed information will be provided about phosphorene deposition using the abovementioned and other methods. Phosphorene demonstrates instability under ambient conditions, which is the main obstacle for its practical applications. Various studies have been conducted in the past to investigate the mechanism of the degradation of phosphorene and passivation techniques to resolve its problem of instability under ambient conditions. To know the various fundamental properties correctly, the stability of this 2D material is very important, which can be achieved by novel passivation strategies. Detailed passivation strategies of phosphorene are elaborated in this chapter. The effects of the passivation layers composition on the thermal stability of phosphorene are also provided. Different growth techniques are described to deposit the passivation layers without altering the properties of phosphorene. To understand the different properties of passivated phosphorene, different measurement techniques such as X-ray diffraction (XRD), Raman spectroscopy, optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) are discussed in this chapter. The effects of annealing temperatures on the properties of passivated phosphorene are discussed in detail. Finally, an overview on the utilization of phosphorene for a variety of applications is also given. A detailed study about 2D phosphorene/3D materials-based next-generation devices are presented in this chapter. The roadmaps to address present challenges for phosphorene are investigated as the properties of this material are very appropriate for next-generation devices. The information presented in this chapter will accelerate the further development of high-performance phosphorene-based electronics and optoelectronics devices. © 2022 selection and editorial matter, Ashish Raman, Deep Shekhar and Naveen Kumar; individual chapters, the contributors.Item Improving the Cu2ZnSn(S,Se)4-Based Photovoltaic Conversion Efficiency by Back-Contact Modification(Institute of Electrical and Electronics Engineers Inc., 2021) Sengar, B.S.; Garg, V.; Siddharth, G.; Kumar, A.; Pandey, S.K.; Dubey, M.; Atuchin, V.V.; Kumar, S.; Mukherjee, S.Back-contact modification using a 10-nm ZnS layer in CZTSSe-based solar cell can play a crucial role in improving photovoltaic conversion efficiency. An ultrathin layer of ZnS is deposited over Mo-coated soda lime glass substrate before depositing CZTSSe using sputtering. The crystal structure of deposited CZTSSe thin films over ZnS is recognized as (112)-oriented, polycrystalline in nature, and free from the presence of any secondary phases such as Cu2(S,Se) or Zn(S,Se). The bandgap of CZTSSe thin films deposited over ultrathin ZnS is observed to increase from 1.49 (deposited over Mo directly) to 1.58 eV at room temperature, as determined by spectroscopic ellipsometry. In addition, numerical simulation has been performed using SCAPS software. The impact of ZnS layer has been simulated by using the defects in the absorber and at the interface of ZnS/CZTSSe. The simulated results have been validated with experimentally fabricated CZTSSe device. Simulated device with ZnS intermediate layer is observed to give rise to a photovoltaic conversion efficiency of 15.2%. © 1963-2012 IEEE.Item 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.Item 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.Item Theoretical investigation of electronic and optical properties of doped and defective MoSe2 monolayers(Springer, 2023) Vinturaj, V.P.; Yadav, A.K.; Jasil, T.K.; Kiran, G.; Singh, R.; Singh, A.K.; Garg, V.; Pandey, S.K.In this work, we have investigated the various electronic and optical properties of undoped molybdenum diselenide (MoSe2) monolayer, such as band structure, density of states, electron density, dielectric function, refractive index, extinction coefficient, reflectivity and energy loss function using density functional theory. Additionally, substitutional doping using niobium (Nb) and manganese (Mn) atoms and introducing defects in undoped MoSe2 lattice were investigated to know the detailed effect of the same on its properties. It is found that the undoped MoSe2 monolayer demonstrates a direct energy bandgap of ~1.44 eV, which reduces after Mn, Nb doping and after introducing Mo, Se vacancy. The energy bandgap attains a very small value 0.2 eV after introducing Se vacancy defect in MoSe2 lattice. The extinction coefficient of MoSe2 monolayer demonstrates a significant increase from 1.79 to 2.66 a.u. after introducing the Mo vacancy in the undoped lattice. The variation of semiconductor to nearly semi-metallic character of MoSe2 by introducing defects makes it very suitable for the application in high-performance solar cells, photo-electrochemical cells, sensors and biosensor applications. © 2023, Indian Academy of Sciences.Item 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.Item Unveiling the Potential of Bismuth Oxy-Iodide (BiOI)-Based Photovoltaic Device for Indoor Light Harvesting(Institute of Electrical and Electronics Engineers Inc., 2023) Manjhi, S.; Siddharth, G.; Pandey, S.K.; Sengar, B.S.; Dwivedi, P.; Garg, V.Indoor photovoltaics (IPVs) have piqued the interest of many because of their potential to power small and portable electronics and photonic devices. This work investigates one of the exemplary perovskite inspired materials (PIMs), bismuth oxy-iodide (BiOI). In order to explore the potential of BiOI in the indoor environment, the baseline model of BiOI device [indium tin oxide (ITO)/NiOx/BiOI/ZnO/Contact] is developed using the experimental results of a recent study with a power conversion efficiency (PCE) of 4%. The performance of the proposed device is fine-tuned by investigating the effect of: 1) absorber thickness and defect density and 2) valence band offset (VBO) between the hole transport layer (HTL) and absorber interface (NiOx/BiOI) along with the interface defect density. Furthermore, the series and shunt resistance of the device is optimized. Additionally, the performance of the optimized device is investigated under different WLED light intensities. Finally, after optimizing the device under WLED illumination, the best performance parameters achieved are Jsc : 1.83 mA/cm2, Voc : 1.33 V, FF: 85.91%, and PCE: 40%. Moreover, the optimized device performance under different indoor light sources: WLED, halogen, and compact fluorescent lamps (CFLs), has been performed to estimate the performance under widely utilized lighting sources. © 1963-2012 IEEE.Item Performance assessment of pocket tunnel FET and accumulation mode FET for detection of streptavidin protein(Institute of Physics, 2023) Jadhav, A.; Yadav, S.; Pandey, S.K.; Garg, V.; Dwivedi, P.In this paper, Dielectrically Modulated (DM) pocket Tunnel Field Effect Transistor (TFET) and Accumulation Mode Field Effect Transistor (AMFET) biosensors are examined for the Sensitivity estimation of different thicknesses of biotarget (Streptavidin)/bioreceptor (Biotin)/silica binding protein (SBP or APTES) biomolecules with a fully filled and partially filled cavity. The sensitivity parameter is based on realistic process detection and is calculated as the ratio of biotarget to bioreceptor drain current for neutral and charged biomolecules. The effect on the sensitivity for a filled cavity is observed for: a) varying the thickness of streptavidin and Biotin for fixed SBP (APTES) thickness, b) varying the thickness of streptavidin and APTES for fixed biotin thickness, for both Pocket TFET and AMFET. The maximum sensitivity is observed in 4 nm thick streptavidin for the front gate voltage V fg: −3.8 V and V fg: −1.6 V for pocket TFET and AMFET, respectively. © 2023 IOP Publishing Ltd.Item 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.Item 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.