BITS Faculty Publications
Permanent URI for this communityhttp://localhost:4000/handle/123456789/1867
Browse
33 results
Search Results
Item Tailoring of the transfer characteristics of nanowire-based GAA-FETs through the channel defects and its effect on the energy-current spectrum(Elsevier, 2025-11) Sarkar, NiladriStudies are performed to investigate the effect of channel defects on the transfer and output characteristics of Nanowire-GAA-FETs. It is observed that the transfer characteristics can be tuned by invoking defect-induced scattering potential in the nanowire channel. Here, the channel scattering potentials chosen are step-shaped and pulse-shaped. The effect of such potentials on the energy-current spectrum of the nanowire device is also studied. It is observed that the normalized energy-current spectrum shrinks due to scattering potential. This results in the early triggering of the device saturation. Also, it is observed that the energy-current spectrum gets enhanced as the gate voltage of the device is increased. This signifies the role of channel currents of different energies in the transport mechanism. Here, the effect of channel defects on device saturation current is corroborated with the corresponding impact on the energy-current spectrum of the nanowire device. This work explains the implication of the modified energy-current spectrum under defect-induced scattering potentials and its effect on the device transfer characteristics. Hence, this idea can be extended to tailor the transfer characteristics through intentionally and unintentionally invoked channel defects on low-dimensional FETs. Also, we have studied the effect of defects on the transconductance, threshold voltage and the subthreshold swing of nanowires FETs. Here, we compared the simulated results with the experimental results of a real GAA-based biosensor.Item Transport properties in a two-dimensional Su–Schrieffer–Heeger model in quantum Hall regime(IOP, 2025-09) Bandyopadhyay, Jayendra N.; Sarkar, NiladriWe investigate the transport properties of a two-dimensional Su–Schrieffer–Heeger (2D SSH) model in the quantum Hall regime using non-equilibrium Green’s function formalism. The device Hamiltonian, where the 2D SSH model serves as the channel, is constructed using a nearest-neighbor tight-binding model. The effect of an external perpendicular magnetic field is incorporated into the contacts via Peierls substitution. We observe a transition from a gapped phase to a flat band regime at zero energy by varying the magnetic field. This transition is characterized by the emergence of highly localized states in the bulk or edges, which we observe by calculating local density-of-states. We analyze transport in the system along two directions (x and y) via transmission measurements, indicating a magnetic field-induced transition from insulating to metallic phase. The study of the energy spectrum of the system shows the formation of Landau levels (LLs). Moreover, the quantum number of the non-degenerate and degenerate LLs (transmission modes) can be any integer or an odd integer, depending on diagonal, inter-cell, and intra-cell hopping strengths. From the analysis of the transport properties along the y-direction, we find that edge modes play a crucial role in facilitating ballistic transport.Item The effect of quantum confinement and the role of electron-phonon interaction on the band gap shrinkage of some II-VI semiconductors(Elsevier, 2024-11) Sarkar, NiladriThe role of electron-phonon interaction in band gap shrinkage for some II-VI bulk and low-dimensional semiconductors is investigated in this work. The variation of the energy band gap is studied as a function of temperature using Varshni's, Vina's, and Passler's relations. It is observed that the change in the energy band gap is affected due to the quantum confinement as the dimensionality of these semiconductors is decreased.Item A study of the tunability of armchair graphene nano ribbon based device channels under spatially varying electric fields in quantum hall effect regime(Springer, 2025-01) Sarkar, NiladriStudies are performed to investigate the flexibility of Armchair Graphene Nano Ribbon (AGNR) based nanoscale channels for electronic and spintronic devices. The role of the spatially varied Electric fields on the bandstructures, Local Density of States (LDOS), Landau Levels, and the Transmission functions of AGNR channels are studied under the Quantum Hall Effect (QHE) regime. Here, the electric potential across the transverse direction is modulated sinusoidally. Also, the electric field is spatially varied exponentially and hyperbolically across the transverse direction. The nature of the Quantum Landau levels(QLLs) show variations in the sub-bands that collapse for constant, exponential, and hyperbolic electric fields and show an oscillatory nature for the sinusoidal field. This is also reflected in the LDOS plots, which change due to the intermixing of the sub-bands and spatial variation of the transverse electric fields. This intermixing of the QLLs sub-bands suppresses the QHE regime’s cyclotron motion. Hence, applying electric and magnetic fields provides a picture of the tunability of AGNR channels.Item Suppression superconductivity in Bi-2223 by light(DAE solid state physics, 2005) Sarkar, NiladriAll high temperature superconductors (HTSC) contain crystal planes consisting only copper and oxygen atoms in a square lattice and superconductivity is achieved by introducing charge carriers into copper oxide insulators. Local perturbation in Cu2O plane suppresses superconductivity by strongly affecting the electronic environment. We use photoinduced electronic modification of Cu ion in CuO2 plane to investigate effect of local perturbation in Bi2Sr2Ca2Cu3O10+δ (Bi-2223)Item Photoinduced Suppression of Superconductivity in Bi2Sr2Ca2Cu3O10+δ(ARXIV, 2006-04) Sarkar, NiladriSuperconductivity in high temperature superconductors is achieved by introducing charge carriers into cuprate insulators containing CuO2 planes. Perturbation in these CuO2 planes suppresses superconductivity by strongly affecting the electronic environment. Here we have use photoinduced electronic modification of Cu ion in CuO2 plane to investigate the effect of local perturbation in Bi2Sr2Ca2Cu3O10+δ. This method has been used to suppress superconducting transition temperature Tc. We show that our results on photoinduced suppression of superconductivity are consistent with a scenario based on pinning of fluctuating stripes in Bi2Sr2Ca2Cu3O10+δ.Item Development of PIC-FDTD code for beam-wave interaction study in ‘PASOTRON’(IEEE, 2015-01) Sarkar, NiladriPlasma-assisted high power microwave source `PASOTRON' is being developed at a few places internationally to utilize plasma channel transport of the beam through Slow Wave Structure (SWS) to significantly reduce the size and weight in conventional linear high power microwave (HPM) sources by eliminating the need for the applied axial magnetic field [1-2]. In this device, very strong non-linear interaction between electron beam and electromagnetic wave can occur, thus making analytical design very cumbersome. Consequently, a particle simulation code is very much required to make its design simpler. We have made an efforts to study beam wave interaction in plasma filled SWS, which is a backward wave oscillator (BWO). The aim is to develop a particle-in-cell finite-difference-time-domain (PIC-FDTD) code [3] using MATLAB for the simulation of beam-wave interaction in the PASOTRON. The updating equations for electromagnetic fields are formulated using FDTD in cylindrical coordinate system since the SWS geometry is axially symmetric. In order to examine the field configuration in 3D, a field solver is implemented using the BOR-FDTD (Body of revolution FDTD) [4]. The results are being compared with MAGIC [5] tool software to validate the analysis. The results of this analysis will be presented.Item PIC-FDTD code for beam-wave interaction analysis in rippled wall slow wave structure(IEEE, 2015) Sarkar, NiladriSummary form only given. A plasma-assisted high power microwave (HPM) source `PASOTRON' is being developed at CSIR-CEERI, where a rippled wall waveguide is used as slow wave structure (SWS) 1 . In this device, very strong non-linear interaction between electron beam and electromagnetic wave can occur, making analytical design very cumbersome. So, a particle simulation code is highly required to make its design simpler. In this work an effort has been made and a particle-in-cell finite-difference-time-domain (PIC-FDTD) code is developed. In designing the field solver for this code, the FDTD algorithm2 is taken up as the method of choice as it allows having frequency domain analysis by applying a fast Fourier transform. The time component in the FDTD code allows the particle wave interaction to be solved self-consistently wherein the Yee's grid2 scheme for the field arrangement ensures that the divergence free nature of the electromagnetic waves is maintained even after the curl equations are discretized. The charge densities due to the particles are interpolated to the grids using the PIC method3. The particle push is implemented using the Boris push method which takes care of the translational motion due to the electric field as well as the rotational motion due to the magnetic field. The current due to particle movement is calculated on the grid using a charge conservation scheme. The phase space patterns produced by the code are then compared with the published results and with the MAGIC simulation software. The axial phase space plots are found to be similar to those which are published elsewhere4 and also to those which are obtained using MAGIC software tool. The results of these efforts will be presented.Item Application of the self-consistent quantum method for simulating the size quantization effect in the channel of a nano-scale dual gate MOSFET(AIP, 2015-06) Sarkar, NiladriSelf-Consistent Quantum Method using Schrodinger-Poisson equations have been used for determining the Channel electron density of Nano-Scale MOSFETs for 6nm and 9nm thick channels. The 6nm thick MOSFET show the peak of the electron density at the middle where as the 9nm thick MOSFET shows the accumulation of the electrons at the oxide/semiconductor interface. The electron density in the channel is obtained from the diagonal elements of the density matrix; [ρ]=[1/(1+exp(β(H − μ)))] A Tridiagonal Hamiltonian Matrix [H] is constructed for the oxide/channel/oxide 1D structure for the dual gate MOSFET. This structure is discretized and Finite-Difference method is used for constructing the matrix equation. The comparison of these results which are obtained by Quantum methods are done with Semi-Classical methods.Item Investigation of the effect of scattering centers on low dimensional nanowire channel(AIP, 2018-05) Sarkar, NiladriIn this work, we studied the effect of scattering centers on the electron density profiles of a one dimensional Nanowire channel. Density Matrix Formalism is used for calculating the local electron densities at room temperature. Various scattering centers have been simulated in the channel. The nearest neighbor tight binding method is applied to construct the Hamiltonian of nanoscale devices. We invoke scattering centers by adding local scattering potentials to the Hamiltonian. This analysis could give an insight into the understanding and utilization of defects for device engineering.