Research

Doctoral Thesis

My doctoral Research involves Terahertz electronics and metamaterials.

My Achievements:

1. Finalists of Best Paper Award, IEEE conference on Nanotechnology, 2019, Macau SAR, China.

Graduate Thesis

My Masters Thesis Papar is available here.

You can also see my Thesis Defense Presentation here.

Thesis Title

MODELING OF SPECTRAL BROADENING AND PHOTORESPONSE IN III-V INFRARED SENSORS INCORPORATING LOW DIMENSIONAL QUANTUM CONFINED SYSTEMS

Research

Expertise

Device Simulation

1. NEGF based simulation

for modeling of transport characteristics of low

dimensional quantum

Confined System

2.Compact Modeling for

inter-subband

photo-detectors

Light-Matter Interaction Modeling

1. Modeling the non-linear electron-photon interaction

and carrier lifetime

2. simulation of

photoresponse enhanced by

Localized Surface Plasmon

Resonance

Background

The fact of infrared emission from all objects at all temperatures above absolute zero has created a vast range of applications for infrared imaging. Though HgCdTe photo-detectors are the state-of-the-art choice for infrared detection, it has limitations due to its less mature II-VI material technology. Of late, some infrared detectors made of quantum confined system have shown promising features to outperform MCT detectors; such as- Quantum Wells benefitting from a more mature III-V growth technology, high temperature operation due to “phonon bottleneck” in Quantum Dot , and Quantum-dot-in-a-well combining both of the above mentioned advantages. One of the fundamental limitations associated with QD is inhomogeneous broadening due to large size-distribution in QD, typical FWHM being 40—50meV limiting the detectors' performance requiring fine spectral resolution. This can be improved in vertical coupling of QDs which unfortunately reduces detectivity in turn. While light enhancement within a narrow layer is a possible solution of regaining the detectivity, excessive light condensation introduces homogeneous broadening. So it remains a challenge to find the optimal window of nominal spectral broadening.

Thesis Supervisor

Dr. Farseem Mannan Mohammedy

Associate Professor,

Department of Electrical and Electronic Engineering,

Bangladesh University of Engineering and Technology

Objectives of the thesis

The objectives of this research with specific aims are as follows:

1) To develop a model to solve the band structures and subbands in the conduction band regions of a generic nano-structure device.

2) To develop a model for calculating photo-response of quantum dot and quantum well infrared photo-detector.

3) To calculate the shift in peak detection wavelength with the variation of quantum dot size, shape and alloy composition.

4) To observe the homogeneous broadening of photo-response spectrum due to light condensation in active region of quantum well photo-detector.

Outcome of thesis

The outcomes of this research are as follows:

a) Simulation tools to study the dynamics of low dimensional quantum dot photo-detector devices when input voltage, geometric dimensions, alloying composition and temperature vary.

b) A model of the photo-response behavior of quantum well infrared photo-detector in the limit of strong electron-photon coupling, especially when light itself governs the band-structure of the device.

Research Methodology

MATLAB based simulator is developed to design the basic unit of semiconducting nano-structured infrared detector (i.e.- quantum well and quantum dot in a well infrared detector) and behavior of the device is studied under dark condition, weak illumination and strong illumination. Through the NEGF Formalism, the carrier transport equation is solved under effective mass approximation. The density of states and the carrier density of the device is determined from the carrier dynamics. The intersubband photo-current spectrum is solved as a function of applied electric field, temperature, and volume density of photon inside the active region. For infrared detectors housing quantum dots, the position of peak wavelength in the photocurrent spectrum is observed as the geometric size and stoichiometry of the individual dot islands are varied and a closed form equation governing the relation between dot size, alloy composition and peak wavelength is established. Also the possibility of two-color detection mechanism at the limit of strong non-linear interaction between electron and photon using the simplest possible device structure is investigated.

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Undergraduate Thesis

Thesis Title

Modeling Quantum Dot in a Well Infrared Photodetector by NEGF Method

Thesis Supervisor

Supervised by: Dr. Farseem Mannan Mohammedy

Also we got valuable suggestion from : Dr. Anisuzzaman Talukder, Md. Zunaid Baten (PhD in University of Michigan Ann Arbor), Ahmad Zubair (PhD in MIT), Redwan Noor Sajjad (PhD in university of Virginia), Sishir Bhowmick (PhD at University of Michigan Ann Arbor)

Special Thanks to: Professor Supriyo Datta (Purdue University)

Motivation behind the thesis

QD photodectors, among many field of applications, will probably be most interesting if we can use it in Night Vision Camera, i.e. thermal imaging.

Electron in QD is like “particle in a 3D box”, its energy bands are discrete, spike-type Density of State. Thats why Quantum Dot is called “Artificial Atom”.

Due to this atom-like behavior , QD detector is fundamentally resistant to thermal noise. Unfortunately, we still have to operate these QD detectors at very low temperature, say, at 80 degree kelvin, and the cooling system increases both cost and size of detectors.

However, if researchers can find a way to remove some problems in QD fabrication technique (i.e. uniform growth of QDs), it will definitely outdo all present IR detectors both in terms of performance and costing. Thats the key for us, the engineers !