Swaroop Ganguly

Bio: Swaroop Ganguly is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Transistor & High-electron-mobility transistor. The author has an hindex of 13, co-authored 156 publications receiving 1154 citations. Previous affiliations of Swaroop Ganguly include University of Texas at Austin & Indian Institutes of Technology.

Bulk Planar Junctionless Transistor (BPJLT): An Attractive Device Alternative for Scaling

Abstract: We propose a novel highly scalable source-drain-junction-free field-effect transistor that we call the bulk planar junctionless transistor (BPJLT). This builds upon the idea of an isolated ultrathin highly doped device layer of which volume is fully depleted in the off-state and is around flatband in the on-state. Here, the leakage current depends on the effective device layer thickness, and we show that with well doping and/or well bias, this can be controllably made less than the physical device layer thickness in a bulk planar junction-isolated structure. We demonstrate by extensive device simulations that these additional knobs for controlling short-channel effects reduce the off-state leakage current by orders of magnitude for similar on-state currents, making the BPJLT highly scalable.

Effect of Band-to-Band Tunneling on Junctionless Transistors

Abstract: We evaluate the impact of band-to-band tunneling (BTBT) on the characteristics of n-channel junctionless transistors (JLTs) A JLT that has a heavily doped channel, which is fully depleted in the off state, results in a significant band overlap between the channel and drain regions This overlap leads to a large BTBT of electrons from the channel to the drain in n-channel JLTs This BTBT leads to a nonnegligible increase in the off-state leakage current, which needs to be understood and alleviated In the case of n-channel JLTs, tunneling of electrons from the valence band of the channel to the conduction band of the drain leaves behind holes in the channel, which would raise the channel potential This triggers a parasitic bipolar junction transistor formed by the source, channel, and drain regions induced in a JLT in the off state Tunneling current is observed to be a strong function of the silicon body thickness and doping of a JLT We present guidelines to optimize the device for high on-to-off current ratio Finally, we compare the off-state leakage of bulk JLTs with that of silicon-on-insulator JLTs

Enhanced Electrostatic Integrity of Short-Channel Junctionless Transistor With High- $\kappa$ Spacers

Abstract: We propose the use of a high-κ spacer to improve the electrostatic integrity and, thereby, the scalability of silicon junctionless transistors (JLTs) for the first time. Using extensive simulations of n-channel JLTs, we demonstrate that the high-κ spacers improve the electrostatic integrity of JLTs at sub-22-nm gate lengths. Electric field that fringes through the high-κ spacer to the device layer on either sides of the gate results in an effective increase in electrical gate length in the off-state. However, the effective gate length is unaffected in the on-state. Hence, the off-state leakage current is reduced by several orders of magnitude with the use of a high-κ spacer with concomitent improvements in the subthreshold swing and drain-induced barrier lowering. A marginal improvement in the on-state current is observed with the use of the high-κ spacer, and this is related to the reduction in parasitic resistance in the silicon under the spacer due to fringe fields.

Graphene nanosheets derived from plastic waste for the application of DSSCs and supercapacitors

Abstract: The present study reports the upcycling process of waste plastics into value-added product graphene nanosheets (GNs) and their subsequent applications in dye sensitized solar cells (DSSCs) and supercapacitors. Bentonite nanoclay has been used as an agent for the degradation of waste plastics with two step pyrolysis processes at 450 °C and 945 °C in an inert atmosphere of N2 gas to obtain GNs. The GNs with few layers were confirmed by the RAMAN spectroscopy, XRD and HRTEM analyses. Further, FT-IR and EDX analyses also performed for the identification and quantitative analysis of functional groups in GNs. The GNs thus synthesized from plastic waste have been used for the fabrication of DSSCs and supercapacitors. The DSSC fabrication with GNs as part of photo-anode with polymeric electrolyte showed a high fill factor of 86.4% and high Voc of 0.77 V, which were also supported by the computational findings. On the other hand, the utilization of GNs as an active layer material of supercapacitor electrodes offered a high specific capacitance of 398 F/g with a scan rate of 0.005 V/s. The supercapacitor also exhibited significant energy density (Ed) and power density (Pd) of 38 Wh/kg and 1009.74 W/kg, respectively. Thus, the process illustrated the utility of waste plastics upcycling for conservation of EEE i.e., ecology, economy and energy for better tomorrow.

Double-Channel AlGaN/GaN High Electron Mobility Transistor With Back Barriers

Abstract: We have developed a double-channel high electron mobility transistor with back barriers for carrier confinement. We have observed that the double-channel devices may suffer from the lack of gate control particularly for the lower channel. However, the problem can be contained by using a suitable back barrier for the lower channel. The double-channel back-barrier devices show good current gain and power gain cutoff frequencies. These devices can be operated with excellent gain linearity up to a larger value for input power and frequency.

Crystal engineering: from molecule to crystal.

Abstract: How do molecules aggregate in solution, and how do these aggregates consolidate themselves in crystals? What is the relationship between the structure of a molecule and the structure of the crystal it forms? Why do some molecules adopt more than one crystal structure? Why do some crystal structures contain solvent? How does one design a crystal structure with a specified topology of molecules, or a specified coordination of molecules and/or ions, or with a specified property? What are the relationships between crystal structures and properties for molecular crystals? These are some of the questions that are being addressed today by the crystal engineering community, a group that draws from the larger communities of organic, inorganic, and physical chemists, crystallographers, and solid state scientists. This Perspective provides a brief historical introduction to crystal engineering itself and an assessment of the importance and utility of the supramolecular synthon, which is one of the most important concepts in the practical use and implementation of crystal design. It also provides a look to the future from the viewpoint of the author, and indicates some directions in which this field might be moving.

Semiconductor Spintronics

Abstract: Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field

The Radical-Pair Mechanism of Magnetoreception.

Abstract: Although it has been known for almost half a century that migratory birds can detect the direction of the Earth's magnetic field, the primary sensory mechanism behind this remarkable feat is still unclear. The leading hypothesis centers on radical pairs—magnetically sensitive chemical intermediates formed by photoexcitation of cryptochrome proteins in the retina. Our primary aim here is to explain the chemical and physical aspects of the radical-pair mechanism to biologists and the biological and chemical aspects to physicists. In doing so, we review the current state of knowledge on magnetoreception mechanisms. We dare to hope that this tutorial will stimulate new interdisciplinary experimental and theoretical work that will shed much-needed additional light on this fascinating problem in sensory biology.

Junctionless Tunnel Field Effect Transistor

Abstract: In this letter, a double-gate junctionless tunnel field effect transistor (JL-TFET) is proposed and investigated. The JL-TFET is a Si-channel heavily n-type-doped junctionless field effect transistor (JLFET), which uses two isolated gates (Control-Gate, P-Gate) with two different metal work-functions to behave like a tunnel field effect transistor (TFET). In this structure, the advantages of JLFET and TFET are combined together. The simulation results of JL-TFET with high- $k$ dielectric material (TiO2) of 20-nm gate length shows excellent characteristics with high $I_{{\rm ON}}/I_{{\rm OFF}}$ ratio $(\sim 6\times 10^{8})$ , a point subthreshold slope (SS) of ${\sim}{\rm 38}~{\rm mV}$ /decade, and an average SS of ${\sim}{\rm 70}~{\rm mV}$ /decade at room temperature, which indicates that JL-TFET is a promising candidate for a switching performance.

Design of Nanostructured Solar Cells Using Coupled Optical and Electrical Modeling - eScholarship

Abstract: Design of Nanostructured Solar Cells Using Coupled Optical and Electrical Modeling Michael G. Deceglie † , Vivian E. Ferry ‡ , A. Paul Alivisatos ‡ , and Harry A. Atwater* ,† Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California 91125, United States Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States Abstract: Nanostructured light trapping has emerged as a promising route toward improved efficiency in solar cells. We use coupled optical and electrical modeling to guide optimization of such nanostructures. We study thin-film n-i-p a-Si:H devices and demonstrate that nanostructures can be tailored to minimize absorption in the doped a-Si:H, improving carrier collection efficiency. This suggests a method for device optimization in which optical design not only maximizes absorption, but also ensures resulting carriers are efficiently collected. Keywords: Thin film solar cells, plasmon, nanophotonic, light trapping, simulation, device physics, silicon, photovoltaics In order to maximize solar cell efficiency, it is necessary to optimize both the electrical device physics and the optical absorption of the device. Typically, these two problems are treated separately,