Department of Physics

Fabrication of Zinc Oxide (ZnO) Nanorods on Aluminium Doped ZnO (AZO) Seeding Layers

Tue, 03 Mar 2026 00:00:00 GMT

Fabrication of Zinc Oxide (ZnO) Nanorods on Aluminium Doped ZnO (AZO) Seeding Layers Hossain, Mukul Aluminium-doped zinc oxide (AZO) thin films and ZnO nanorods (NRs) were synthesized and characterized to explore their structural, optical, and electrical properties. AZO seed layers with varying Al concentrations 2, 3, 5, and 8 mol% were deposited on soda-lime glass via spin coating, followed by hydrothermal growth of ZnO NRs. XRD and SEM confirmed vertically aligned, c-axis-oriented nanorods, with morphology influenced by doping and annealing temperature. Optimal crystallinity was achieved at 250 °C, while higher temperatures led to lattice relaxation and reduced structural quality. Photoluminescence revealed UV near-band-edge emission (~380 nm) and visible deep-level emission (500–700 nm), with DLE intensity suppressed at 8 mol% doping, indicating reduced defect density. Both AZO and ZnO NRs showed high optical transparency, and band gaps ranged from 3.44–3.55 eV (AZO) and 3.05–3.15 eV (ZnO NRs), tunable via Al doping. The electrical conductivity and film thickness were strongly influenced by both Al concentration and annealing conditions. The favorable combination of structural integrity, high transparency, tunable band gaps, and improved conductivity renders these AZO/ZnO nanostructures promising candidates for application in a wide range of optoelectronic devices. This thesis is submitted for the degree of Master of Philosophy.

Genesis and Intensification of Tropical Cyclone of North Indian Ocean Using Numerical Model

Wed, 05 Nov 2025 00:00:00 GMT

Genesis and Intensification of Tropical Cyclone of North Indian Ocean Using Numerical Model Rabbi, A. H. M. Fazla Tropical cyclones (TCs) represent one of the most prevalent and devastating forms of natural disasters. Despite their significant impact, accurately predicting tropical cyclones (TCs) remains a challenging endeavour due to the complexities involved. Over the past fifty years, numerous theories have been proposed to elucidate the genesis and intensification of TCs. However, no single theory has been able to explain the genesis and intensification of TC fully. Consequently, there remains a division among scientists regarding a comprehensive understanding of TC formation. The current study conducted in the North Indian Ocean (NIO) aims to provide new insights into the various stages involved in the genesis and intensification of TCs from low-pressure systems (LPS). This study employed data from the NCEP FNL reanalysis of 1x1 degree resolution as input for the Weather Research and Forecasting (ARW) model of version 4. We utilized the domain configuration of child and parent domain through one-way nesting. A combination of Kain-Fritsch (new Eta) scheme for cumulus parameterization and the WRF Single-Moment 6 class (WSM6) graupel scheme for microphysics was incorporated in model run. The findings indicate that upper wind circulations and the geographical positioning of LPS are critical to the genesis and intensification of TCs. An upper cyclonic circulation located to the left or northwest of the centre, along with an anticyclonic circulation or poleward winds to the right or northeast, significantly increases the likelihood of TC formation. Furthermore, the dominance of upper-level westerlies over LPS creates favourable conditions for the genesis of TCs. Easterly winds tend to hinder both genesis and intensification in the NIO. Additionally, proximity to coastal regions can adversely affect TC genesis. Vertical wind shear (VWS) values between 3 and 10 m/s are crucial for the transformation of LPS into TCs. Sustained declines in central pressure and mid-level Geopotential Height (GPH) foster an environment conducive to both the TC genesis and intensification. Sea Surface Temperatures (SST) exceeding 26°C and a radial gradient in SST enhance the likelihood of TC genesis. The warming of the inner core of LPS is favourable for both the genesis and 8 heightened intensity of TCs. Minimum potential vorticity (PV) of 1 at the upper level is critical for TC genesis, with a sustained increase in upper PV over time supporting further intensification. The Convective Available Potential Energy (CAPE) was lowest at the centre of the LPS, with CAPE values ranging from 2000 to 4000 J/kg within the LPS, which are conducive to tropical cyclone genesis.. A maximum CAPE value of 5000 J/kg during the genesis stage indicates potential for high-intensity TCs. Elevated relative humidity at mid-level altitudes and a symmetric cloud band pattern around the centre of the LPS significantly promote the genesis of TCs and enhance the potential for high-intensity TCs. The boundary layer air is substantially influenced by heat flux from the underlying warm sea surface. Continuous enhancement of upward vertical heat flux accelerates the genesis and intensification of TCs. Despite differences in data resolution, scale, and domain configuration, the model results and analyses derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) concerning TC genesis and intensification substantially corroborate each other. Thus, the outcomes of this study are deemed reliable. The insights acquired from this research are invaluable in enhancing accurate predictions of TC genesis and intensification in the NIO. This study will serve as a guiding tool for governmental departments in Bangladesh and India, assisting in the protection of human life and the mitigation of damage to property, infrastructure, environment, and biodiversity resulting from TCs. Various government agencies will have sufficient time to be well-equipped to execute timely responses and implement appropriate disaster management measures. This thesis is submitted for the degree of Doctor of Philosophy.

STUDY OF SOME COMMERCIALLY FABRICATED SEMICONDUCTOR P-N JUNCTION CHARACTERISTICS AND CHARACTERIZATION OF IMPURITY LEVELS PRESENT THEREIN

Sun, 07 Sep 2025 00:00:00 GMT

STUDY OF SOME COMMERCIALLY FABRICATED SEMICONDUCTOR P-N JUNCTION CHARACTERISTICS AND CHARACTERIZATION OF IMPURITY LEVELS PRESENT THEREIN Selima Begum, MS Khondaker The object of present work has been to study junction properties of some commercially available diodes and transistors. We studied over fifty samples out of which twenty were analyzed in details and are reported here. To study the property of depletion layer of p-n junction we carried out a detail C-V measurement. From this study junction capacitance, depletion width, contact potential etc. have been evaluated. From I-V studies (for forward bias and reverse bias conditions) efficiency factor r? has been estimated for large numbers of diodes. These studies indicate the presence of deep impurity centers in most of the samples. To confirm this we carried out detail investigation to detect defect states, if any, and characterized the defect states whenever found. We have observed the presence many and varied deep states both in Si and Ge. The methods used the states are TSCAP and TSC. for characterizing Ip carrying out the investigation we have to construct fixed and variable temperature system, a constant temperature bath and many electronic circuitry needed for our experiments This thesis is submitted for the degree of Master of Philosophy

DESIGN AND CONSTRUCTION OF A COMPUTER AIDED CAPACITANCE TRANSIENT SPECTROMETER FOR THE STUDY OF DEEP DEFECT CENTRES IN SEMICONDUCTORS

Wed, 03 Sep 2025 00:00:00 GMT

DESIGN AND CONSTRUCTION OF A COMPUTER AIDED CAPACITANCE TRANSIENT SPECTROMETER FOR THE STUDY OF DEEP DEFECT CENTRES IN SEMICONDUCTORS BEGUM, MS ZERINA The object of the present work has been to design and construct a computer aided transient capacitance spectrometric system for detection and characterisation of deep defect centres in Semiconductor. It is hoped that the spectrometer would be able to detect, identify and characterise the deep defect centres present in semiconductor devices. It is known that the presence of impurities or lattice defects in a semiconductor crystal creates deep defect centres. The defect states are located deep inside the forbidden zone, which may act either as <■_ «electron/hole traps or recombination centres. So these centres influence the electrical and optical properties of a semiconductor. The identification and study of their characteristics and kinetics would facilitate the understanding of physics of the semiconductor and its devices. The basic idea of a DLTS spectrometer is to implement a “rate window”. There are two methods of implementing the rate window: by the use of (i) a double box car averager or (ii) a Lock-in-amplifier. In the present work we have implemented the rate window with the computer aided electronic circuitry based on the basic principle of box car averager. DLTS spectrometer system is a complicated experimental setup and needs sophisticated instrumentation. To develop our spectrometric system we have used a 710 ACER computer. The main component i.e. the heart of our system is a rapid data acquisition system peculiar to our need and purpose which would collect and store data, for subsequent manipulation, record temperature of the system, and capacitance from a capacitance meter. For the system we need various electronics circuitry including S/H circuit^unity gain amplifier, base line restorer, and pulse amplifier. All these units have been developed and constructed in the laboratory. Other experimental devices and setups such as cryostatic set up, sample assembly etc. have been constructed in the laboratory. Interfacing between the analog world and the computer has been made via interfacing unit, the Keithley made 570 system. The variable width pulse generator and the capacitance meter formp other two major component^ our system. The capacitance meter operates at 1MHz. The necessary softwares needed to run the constructed spectrometer based on BASIC High Level language together with a special software Soft500 have been developed to suit our environment and need. In order to test the performance of our spectrometer system we have used hardware based laboratoiy made artificial and software based computer simulated DLTS signals. A few real samples i.e. Si p-n junctions have been examined and DLTS signals could be detected This thesis is submitted for the degree of Master of Philosophy