Dr. Md. Iqbal Bahar Chowdhury | United International University (original) (raw)

Papers by Dr. Md. Iqbal Bahar Chowdhury

Advances in Mathematics: Scientific Journal, 2020

This paper presents a simple design of a 1-bit pass transistor logic based 'Fast Adder' module im... more This paper presents a simple design of a 1-bit pass transistor logic based 'Fast Adder' module implemented using carbon nanotube field-effect transistors (CNFETs). 'Sum' and 'carry' outputs of the fast adder circuit has been generated using the XOR function and hence, the module uses only 6 transistors. This Fast adder module is implemented in Cadence with 32 nm CNFET technology with 0.9 V as supply. The switching power of this adder has been observed at different states through the simulations using Cadence at 100 MHz input frequency. 0.8 nW is found to be the average switching power in case of no load. Although there is degradation in the outputs for one/two states owing to circuit behavior and CNFET properties, the implemented fast adder is more cost-effective than the conventional adders.

Inserting Quantum wells into solar cells has been a novel technique for producing high efficiency... more Inserting Quantum wells into solar cells has been a novel technique for producing high efficiency third generation solar cells. Here we present a Multi-Quantum-well Dual-Junction GaAs/GaSb solar cell which is simulated using a numerical semiconductor device simulator (Silvaco TCAD) where number of wells is varied to see its effect on single as well as dual junction solar cell and a maximum of 30% efficiency is achieved.

Of various light-trapping schemes commonly employed in the plasmonic solar cells, the photonic cr... more Of various light-trapping schemes commonly employed in the plasmonic solar cells, the photonic crystal back reflectors are proved in the literature to enhance the absorption of photons in the near infra-red wavelength region significantly. In these cells, the photonic crystal back reflectors are usually placed at the bottom of the cell along with diffracting Brag's reflector (DBR). These reflectors block and reflect back the long wavelength light to the absorbing region. Therefore, the absorption of photons in the near infrared region has been significantly increased and the internal quantum efficiency in this wavelength region has been improved resulting in increased power conversion efficiency. In this work an analytical derivation of internal quantum efficiency has been developed to model such effects of photonic crystal back reflector on the internal quantum efficiency of a plasmonic solar cell based on hydrogenated amorphous silicon (a-Si: H) based absorber. The model resul...

2018 International Conference on Computer, Communication, Chemical, Material and Electronic Engineering (IC4ME2), 2018

A specific channel engineering over a cylindrical double gate all around FET (CDGAA FET) is propo... more A specific channel engineering over a cylindrical double gate all around FET (CDGAA FET) is proposed in this work. The engineering is to stack 3 layers of diversely doped silicon in channel region in order to attain a much better carrier concentration in all states of FET operation. This modified FET is termed as channel engineered cylindrical double gate all around FET (CE-CDGAA FET). The simulation results reveal that this modification provides reduced off current (Ioff), greatly enhanced on current (Ion) and boosts the on-off current ratio (Ion/Ioff). The proposed modification also lowers the drain induced barrier lowering (DIBL) and subthreshold swing (SS) compared to CDGAA FET. This evolution allows downscaling a FET up to 3nm channel length with acceptable performance in many of its performance parameters, marking its applicability in VLSI and low power FET applications. A comparative study between CE-CDGAA FET and CDGAA FET is also presented in this work.

2012 International Conference on Devices, Circuits and Systems (ICDCS), 2012

Quantum efficiency of a SiGe solar cell has been developed for box, triangular and trapezoidal do... more Quantum efficiency of a SiGe solar cell has been developed for box, triangular and trapezoidal dosing profiles of Ge in exponentially doped base. The doping dependency of carrier mobility and carrier lifetime, the band-gap narrowing effect due to heavy doping level and velocity saturation effects are considered to deduce the governing differential equation for this model. An elegant exponential approximation technique has been employed to simplify the complicated nature of variable coefficients of the working differential equation. The model results show that the increased Ge-content in the base results in significant improvement in the internal quantum efficiency.

2017 3rd International Conference on Electrical Information and Communication Technology (EICT), 2017

Buried oxide layer in SOI devices creates a few problems such as self-heating, which eventually f... more Buried oxide layer in SOI devices creates a few problems such as self-heating, which eventually flops the possibility of this device for future circuit analysis. A modification over a fully depleted SOI MOSFET merged with cylindrical gate all around (CGAA) structure is proposed in this work to incorporate improved performance along with a possibility to dissipate the heat generated in the device. The buried oxide layer is replaced with thin P+ region and the substrate layer is replaced by a metallic nanowire which is located at the center of the GAA core. The metallic nanowire is shorted with the gate metal to give in strong govern over the flow of the current and helps the device to release its heat easily. This modified structure is termed as silicon on metal (SOM) CGAA FET and was simulated using SILVACO TCAD ATLAS for short technology nodes. To exhibit the superiority of the device the simulation results were compared with CGAA FET. The device shows an improved electrical characteristics and scaling possibility below 10nm technology node over CGAA FET which makes this modified device potentially suitable for future CMOS technology.

Journal of Instrumentation and Innovation Sciences (e-ISSN: 2456-9860), Apr 17, 2021

This work investigates the quantum efficiency of a single-junction gallium arsenide/indium arseni... more This work investigates the quantum efficiency of a single-junction gallium arsenide/indium arsenide (GaAs/InAs)- based quantum well solar cell (QWSC), where GaAs (InAs) acts as a barrier (quantum well) material. The investigation involves a number of simulations carried out by the Silvaco TCAD software tool. The effects of InAs-QWs on carrier absorption and carrier recombination have been thoroughly analyzed. The physics-based analysis reveals that there is a maximum limit of the number of InAs-QWs that can be inserted in the intrinsic absorber layer to achieve optimum quantum efficiency and this limit is set by the competition of the photon absorption and the losses incurred optically as well as electronically in the cell

This work presents some proposals to improve the portability of a recently-reported capacitor-sen... more This work presents some proposals to improve the portability of a recently-reported capacitor-sensor based non- invasive glucometer. These proposals include removal of some hardware such as the dummy capacitor and an OPAMP in one side and the generation of low-frequency, low-voltage ac signal from the microcontroller instead of using separate source in other side. The proposed changes are implemented and tested using the Proteus simulation tool. The results are consistent and optimistic as well and hence, not only prove the validity of the suggested changes but also paves the way for their near-future implementation in hardware with minimal cost and increased portability. A possible double-layer PCB layout design is also presented to demonstrate the cost reduction as well as the improved portability and the wearability of the modified non-invasive glucometer.

2017 20th International Conference of Computer and Information Technology (ICCIT), 2017

In this paper, a cylindrical double gate-all-around technology is merged with junctionless techno... more In this paper, a cylindrical double gate-all-around technology is merged with junctionless technology to maximize gate control as well as to avoid loss due to the formation of junction in the source-channel-drain region. This advancement allows downscaling a junctionless cylindrical double gate all around FET (JL-CDGAA FET) up to 5nm channel length with acceptable performance in many of its parameters. A comparative study between JL-CDGAA FET and GAA FET is also presented in this work.

2021 2nd International Conference on Robotics, Electrical and Signal Processing Techniques (ICREST)

In this work, a cylindrical gate-all-around field-effect transistor (CGAA FET) has been implement... more In this work, a cylindrical gate-all-around field-effect transistor (CGAA FET) has been implemented using gallium arsenide (GaAs) as the channel material instead of the conventional silicon material. The investigations based on the simulations using the Atlas tool of the Silvaco TCAD software prompts out that the GaAs-based CGAA FET is capable of overcoming the short channel effects (SCE) for sub-20 nm technology node and thus, becomes a viable contender to achieve SCE-free sub-20 nm FET devices.

2016 4th International Conference on the Development in the in Renewable Energy Technology (ICDRET), 2016

This work focuses to develop an analytical model of the internal quantum efficiency for a drift-f... more This work focuses to develop an analytical model of the internal quantum efficiency for a drift-field Si-solar cell with non-uniformly and heavily doped emitter region. The resulting mathematical intractability owing to the consideration of all the non-ideal effects have been resolved by employing an elegant approximation technique. The developed model shows that the drift-field solar cells have significantly higher internal quantum efficiency over the uniformly-doped Si-solar cells, particularly for high energy photons.

2020 23rd International Conference on Computer and Information Technology (ICCIT), 2020

This work aims to investigate the effects of thickness variation of the different layers of a qua... more This work aims to investigate the effects of thickness variation of the different layers of a quantum well solar cell on its performance parameters i.e. on the short circuit current and the conversion efficiency. The investigation incurs a number of simulations carried out using the ATLAS tool of Silvaco software. The analysis of the simulated results not only provide a better view as well as a physics-based understanding of the effects of the thickness variation of each layer on the performance parameters but also help optimize these layer thicknesses to achieve the best possible performance, which includes the short circuit current and the conversion efficiency, of a quantum well solar cell.

This work explores the opportunity of the use of graphene as the transparent conducting (TC) laye... more This work explores the opportunity of the use of graphene as the transparent conducting (TC) layer instead of conventional transparent conducting oxide (TCO) such as indium tin oxide (ITO) in the CZTS based solar cells which is recently evolved as one of the most promising thin film solar cells. It has been known that graphene has higher transmittance and conductance and is cheaper than the widely used ITO. Based on the MATLAB simulations, this work proves that graphene can be used as the better alternative than ITO as the transparent conducting layer. Moreover, simulations show that the use of graphene can reduce the amount of CZTS material and hence, reduce the cost of solar cell as optimum absorber width based on maximum possible conversion efficiency is found less for the graphene-TCL based solar cells.

2010 IEEE International Conference of Electron Devices and Solid-State Circuits (EDSSC), 2010

The main objective of this paper is to show that majority carrier current needs to be taken into ... more The main objective of this paper is to show that majority carrier current needs to be taken into account in determining base transit time. In previous analytical works for base transit time, majority carrier current in the base was neglected. In this paper both drift and diffusion currents for electron and hole are considered in obtaining minority carrier profile n(x). In the model, it is assumed that the lateral injection of base current into the active base region is occurred from a source function, g. The energy-bandgap-narrowing effects due to heavy doping, velocity saturation as well as doping and field dependent mobility are considered.

Electronic Design Engineering, 2017

This work presents a SILVACO TCAD based fabrication and device simulation of a top-gated graphene... more This work presents a SILVACO TCAD based fabrication and device simulation of a top-gated graphene field-effect transistor. Effects of channel length and channel doping concentrations on the characteristics curves (transfer and output characteristics) of the GFET are also investigated and analyzed physically to obtain more physical insight.

2015 International Conference on Advances in Electrical Engineering (ICAEE), 2015

This work develops an analytical model of the base transit time for the SiGe-heterojunction bipol... more This work develops an analytical model of the base transit time for the SiGe-heterojunction bipolar transistors (HBT) having non-uniformly and heavily doped base considering the field-dependence of the carrier mobility under moderate-level injection. The proposed model considers all the non-ideal effects found in the literature owing to the non-uniformity and the heavy levels of the base doping. The evolving mathematical intractability has been resolved by applying an exponential approximation technique and the concept of the perturbation theory. Simulation results of the proposed model for the exponentially doped base with three types of Ge-dosing profile (box, trapezoidal and triangular) show that the effects of the field-dependent carrier mobility on the base transit time is significant.

In this work, an analytical model has been developed for the dark saturation current in the heavi... more In this work, an analytical model has been developed for the dark saturation current in the heavily-doped base region of a drift-field Si-solar cell. Unlike the conventional models available in the literature, this model incorporates both the SRH (Shockley-Read-Hall) and the Auger recombination. The mathematical intractability due to this consideration has been resolved by using an elegant exponential approximation technique. The simulations carried out by the developed model shows that the Auger recombination becomes significant even for a 1 µm wide base when surface recombination velocity is lowered to the order of 10^4 cm/sec and/or when the doping level is of the order of 10^19 cm-3 .

This work aims to enhance the conversion efficiency of an organic solar cell (OSC) based on PCDTB... more This work aims to enhance the conversion efficiency of an organic solar cell (OSC) based on PCDTBT/PC71BM material through the optimization of the thicknesses of its different layers, namely- the hole transport layer and the active layer. A numerous simulation runs using a SILVACO Atlas based model have been conducted to determine the optimum thicknesses of the said layers. The effects of the layer thickness variation on the various performance parameters of the OSC are discussed through physics-based analysis, which help determine the optimized thickness. The layer optimization finally yields an improved efficiency of the said OSC ($\approx$S.S%).

The introduction of non-uniform doping profile in the quasi-neutral regions of a solar cell helps... more The introduction of non-uniform doping profile in the quasi-neutral regions of a solar cell helps achieve better performance parameters such as higher conversion efficiency and improved current-voltage characteristics. However, a number of non-ideal effects becomes dominant as the doping level is increased; the transport parameters (i.e. mobility and lifetime) become doping and field dependent, the space-dependency of the bandgap narrowing becomes significant and the Auger recombination mechanism becomes dominant. These effects adversely affect the internal quantum efficiency and hence, need to be considered with great care. Unfortunately, owing to the evolving mathematical intractability, all these effects are not considered simultaneously in the existing models. This work focuses to develop an analytical model for a drift-field Si-solar cell with non-uniformly and heavily doped emitter region where the mathematical intractability problem has been resolved by employing an elegant a...