Sanjoy Deb

Work Function Engineering With Linearly Graded Binary Metal Alloy Gate Electrode for Short-Channel SOI MOSFET

Over the last few decades, silicon-on-insulator (SOI) technology has been identified as one possible solution for enhancing the performance of CMOS because of its numerous advantages over conventional bulk CMOS technology. One of the primary drawbacks of short-channel SOI MOSFET is the degradation of device threshold voltage with decreasing channel length. Drain-induced barrier-lowering (DIBL) effect, generated from high drain bias, is the main cause behind this length-dependent nature of threshold voltage. This “instability” in threshold voltage is responsible for making SOI device design very challenging. The instability that is known as the threshold voltage rolloff restricts further scaling of SOI devices. In this paper, an idea of work function engineering with continuous horizontal mole fraction variation in a binary alloy gate has been proposed and implemented theoretically. Analytical model-based simulation verified that performance of proposed SOI MOSFET is improved as it has higher immunity to DIBL effect.

A two-dimensional analytical-model-based comparative threshold performance analysis of SOI-SON MOSFETs

A generalized threshold voltage model based on two-dimensional Poisson analysis has been developed for SOI/SON MOSFETs. Different short channel field effects, such as fringing fields, junction-induced lateral fields and substrate fields, are carefully investigated, and the related drain-induced barrier-lowering effects are incorporated in the analytical threshold voltage model. Through analytical model-based simulation, the threshold voltage roll-off and subthreshold slope for both structures are compared for different operational and structural parameter variations. Results of analytical simulation are compared with the results of the ATLAS 2D physics-based simulator for verification of the analytical model. The performance of an SON MOSFET is found to be significantly different from a conventional SOI MOSFET. The short channel effects are found to be reduced in an SON, thereby resulting in a lower threshold voltage roll-off and a smaller subthreshold slope. This type of analysis is quite useful to figure out the performance improvement of SON over SOI structures for next generation short channel MOS devices.

Analytical I–V model of SOI and SON MOSFETs: a comparative analysis

A generalised three-interface compact capacitive threshold voltage model for horizontal silicon-on-insulator/silicon-on-nothing (SOI/SON) MOSFET has been developed. The model includes different threshold voltage-modifying short-channel phenomena like fringing field, junction-induced 2D-effects, etc. Based on the threshold voltage model, an analytical current voltage model is formulated from the basic charge control analysis of MOSFET. In order to provide a better explanation to various observations and applicable to short-channel SOI and SON structures, the present current voltage model includes the effect of carrier velocity saturation and channel length modulation. Identical structures for both the devices, SOI and SON, are considered but for SON MOSFET, the buried oxide layer is replaced by air. The performance of the two devices are studied and compared in terms of threshold voltage roll-off, subthreshold slope, drain current and drain conductance. The SON MOSFET technology is found to offer devices with further scalability and enhanced performance in terms of threshold voltage roll-off, sub-threshold slope and greater current derivability, thereby providing scope for further miniaturisation of devices and much better performance improvement.

Response of a Partially Illuminated Photovoltaic P-N Junction Cell†

ABSTRACT A theoretical analysis has been carried out of the problem of response of a partially illuminated photovoltaic cell. The analysis is based on the assumption that the diffusion-driven carriers from the illuminated zone, on crossing the junction, spread out evenly over the same through the majority carrier relaxation process. Experimental results are given in support of the main theoretical deduction. It is found that, as a practical tool for measurement of radiant power, the arrangement does not require correction for end-effect so long as the radiation does not penetrate appreciably into the n-region and has a duration large compared to the minority carrier lifetime in that region.

Particle swarm approach for parameter optimization of quantum well nano structure

Analytical optimization techniques suffer from slow convergence in complex solution space. Heuristics-based swarm intelligence is an efficient alternative to analytical optimization techniques. In this paper, particle swarm optimization approach is utilized for better and efficient nano-device modeling. Mobility of two-dimensional hot electrons in modulation doped square quantum well of AlGaAs/GaAs which is determined using heated drifted Fermi-Dirac distribution function and relevant scattering mechanisms is taken as the fitness/objective function. The 2D carrier concentration, quantum well width and lattice temperature of the quantum well are taken as the input variables. The algorithm with three input variables is then utilized to get optimized values of input parameters to get desired ac and dc mobility values.

Application of Particle Swarm Optimization Algorithm for Better Nano-Devices

Particle swarm optimization, an intelligent soft computing tool is employed to determine the optimized system parameters of GaAs quantum well for better high frequency performance under hot electron condition at room temperature. The energy loss through LO phonon and momentum loss through LO phonon, deformation acoustic phonon and ionized impurity (both background and remote) are incorporated in the present calculations. For a typical dc biasing field, it is possible to predict the optimum values of system parameters like lattice temperature, well width and two-dimensional carrier concentration for realizing a particular high frequency response characterised by well defined cut-off frequency. Such optimization will make feasible the fabrication of a variety of new quantum devices with desired characteristics.

Swarm approach towards better quantum well nanostructure modeling

Particle Swarm Optimization (PSO) Algorithm is employed to determine the optimized system parameters of modulation doped AlxGa1-xAs/GaAs quantum well for better low-power and high frequency response. The mobility (ac and dc) of two-dimensional hot electrons in square quantum well of AlxGa1-xAs/GaAs is computed numerically using heated drifted Fermi-Dirac distribution function and relevant scattering mechanisms. An effectively modeled particle swarm optimization algorithm is used here to get the optimized system parameters for desired high frequency low power consuming and low dimensional devices.

Millimeter and Sub-millimeter wave Response of Two-Dimensional Hot Electrons in double delta doped GaAs Quantum Well

Millimeter and sub-millimeter wave response of two-dimensional hot electrons in double delta doped GaAs quantum well is studied here incorporating deformation potential acoustic, polar optic, ionized background and remote impurity scatterings in the framework of heated drifted Fermi-Dirac distribution function. The inclusion of delta doping is found to enhance the two-dimensional electron density which in turn improves the ac mobility in the GaAs quantum wells thereby providing scope of getting higher speed devices in future.

A NEW METHOD FOR DETERMINING THE SHEET RESISTANCE AND NON-UNIFORMITIES OF THE SKIN LAYER IN PHOTOVOLTAIC DEVICES

ABSTRACT A new technique was developed to determine the skin layer sheet resistance (R o ) of Photovoltaic Devices. Additionally, the technique also enables one to study the distributive nature of series resistance (R s ), non-uniformity of the cell structure in the lateral direction and the variation of R o with intensity. The technique which determines R o by a nondestructive method, also allows one to detect any potentially harmful cracks or nonuniformities in the cells surface and helps design of the actual grid configuration. The technique can be adopted at the initial stage of development of cells at laboratories lacking in high grade infrastructure.

A note on the correct evaluation of junction capacitance of a solar cell

Abstract In the fabrication of low-cost solar cells one has often to contend with finite series and shunt resistances. These tend to give misleading values of the junction capacitance as measured with an ordinary bridge. The problem is discussed analytically and graphical plots are given for determination of the true values from the measured ones. Practical use of these plots is discussed and illustrated with the help of experiments on thin-film Cu2S-CdS solar cells.