98 research outputs found
Technological readiness of Bangladesh's pharmaceuticals industry : preparing for LDC graduation
No full textFahmida Khatun, Syed Yusuf Saadat, Anika Ferdous Richi, Anisha Ushrad Aurchi ; jointly published by Friedrich-Ebert-Stiftung (FES) Bangladesh and Centre for Policy Dialogue (CPD
On chip frequency comb: Characterization and optical arbitrary waveform generation
No full textRecently, on-chip comb generation methods based on nonlinear optical modulation in ultrahigh quality factor monolithic micro-resonators have been demonstrated. In these methods, two pump photons are transformed into sideband photons in a four wave mixing process mediated by the Kerr nonlinearity. The essential advantages of these methods are simplicity, small size, very high repetition rates and sometimes CMOS compatibility. We investigate line-by-line pulse shaping of such combs generated in silicon nitride ring resonators. We demonstrate a simple example of optical arbitrary waveform generation (OAWG) from Kerr comb. We observe two distinct paths to comb formation which exhibit strikingly different time domain behaviors. For combs formed as a cascade of sidebands spaced by a single free spectral range (FSR) that spread from the pump, we are able to compress to nearly bandwidth limited pulses. This indicates high coherence across the spectra and provides new data on the high passive stability of the spectral phase. For combs where the initial sidebands are spaced by multiple FSRs which then fill in to give combs with single FSR spacing, the time domain data reveal partially coherent behavior. We also investigate the behaviors of a few sub-families of the partially coherent combs selected by a pulse shaper. We observe different coherence properties for different groups of comb lines. Furthermore we will discuss an ultrafast characterization techniques called dual comb electric eld cross correlation. This linear technique will provide both low optical power and broader bandwidth capability for full time domain characterization of OAWG from Kerr comb
Anisotropy and Non-Uniformity Effects on the Strain Relaxation in GaInAsP/InP Quantum Wire Structures
No full textEnergy band structures of strained membrane quantum wires considering the redistribution of elastic strain relaxation
No full textFirst-principles investigations of transition metal hyperdoped silicon and germanium for intermediate band engineering
No full textSilicon is the dominant material in the semiconductor industry, massively used in transistors, rectifiers, microchips, and other solid-state electronic devices. On top of that, its optoelectronic properties are largely utilized in photovoltaics, photodiodes, and photodetectors. However, in many optoelectronic devices silicon is limited by its band gap of 1.12 eV (_ = 1,110 nm) which precludes absorption of low energy infrared photons. For example, current photovoltaic devices suffer energy loss to a great extent due to non-absorption of a large portion of the incoming solar spectrum. Additionally, if the photoresponse of silicon could be extended to the infrared, silicon could be used to replace more expensive germanium based detectors.
My thesis research focuses on defect engineering of silicon to extend the photoresponse to the infrared regime. Recently, introducing defects at large concentrations several orders of magnitude larger than the equilibrium solubility limit has emerged as an approach to engineering the optical response of silicon. Specifically my thesis research addresses three aspects of hyperdoped semiconductors, which are as follows. (i) Carrying out first-principles investigations of gold hyperdoped silicon to provide detailed insights into recent extensive experimental investigations. This analysis helps to reveal the origins of the sub band gap optical response observed in this system, as well as to provide insights into the metastability and atomic scale mechanism of the loss of optical response upon thermal annealing. (ii) Moving beyond gold to consider alternative suitable transition metal dopants. It is of interest to identify candidate dopants that enhance optical absorption, and have sufficient solubility in silicon to remain dissolved in the semiconductor at high concentration and/or can become kinetically trapped to mitigate metastability. (iii) Using the insights gained from gold (Au) hyperdoped silicon systems, which have been extensively studied, to extend defect analysis towards gold hyperdoped germanium. This work involves carrying out high-accuracy first-principles modeling of candidate dopant defects in silicon, and assessing their promise for sub band gap absorption.
For gold hyperdoped silicon, first-principles density functional theory is used to first establish the origins of sub band gap optical absorption. While the experimentally synthesized systems likely contain a distribution of gold-related defects, experiments and the electronic structure analysis presented here strongly suggest that substitutional gold is responsible for the optical response. Unfortunately, the experimentally realized system optically deactivates upon thermal treatment. To understand the deactivation, I propose a mechanism for the evolution of atomic structure during thermal relaxation using simulations of energy barrier calculations, diffusion, and defect reactions. The dissociative mechanism, in which diffusion occurs by exchange of substitutional and interstitial sites via vacancy formation and annihilation, is identified as the likely path for deactivation. Further, the experimentally observed lattice contraction is explained by the presence of vacancies and gold-vacancy complexes in excess concentrations. The presence of these vacancies is attributed to the minimization of the strain that arises from the large volume of gold incorporated into silicon.
Towards the goal of identifying candidate hyperdoped materials for advanced optoelectronic devices such as intermediate band photovoltaics, I have carried out a systematic study of transition metal dopants in silicon in search for better dopants. To find other possible candidate dopants that could exhibit infrared absorption and, possibly, better solubility in silicon, I have assessed alternative transition metals such as Mn, Fe, Co, Ni, Cu and Ag using the optical design rules learned from prior investigations of chalcogen hyperdoped silicon. As the gold doped silicon study shows that not only the optical absorption but the (meta)stability of the system is also important, I have included an analysis of solubility and diffusion in silicon. This investigation also provided an opportunity to reassess the properties of transition metal defects in silicon, which had been studied extensively several decades ago, now using modern first-principles methods. As part of this analysis I have summarized their magnetic and electronic structure using density of states, orbital hybridization analysis, and band diagrams. Finally, I have extended the analysis of gold hyperdoped silicon to gold hyperdoped germanium. The relationship between measured carrier decay dynamics and some possible defect configurations are proposed in conjunction with recent experimentally achieved high
concentrations of gold and demonstrated optical response in germanium.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-12-01The student, Naheed Ferdous, accepted the attached license on 2019-10-24 at 14:40.The student, Naheed Ferdous, submitted this Dissertation for approval on 2019-10-24 at 15:00.This Dissertation was approved for publication on 2019-10-31 at 15:49.DSpace SAF Submission Ingestion Package generated from Vireo submission #14517 on 2020-02-28 at 17:21:15Made available in DSpace on 2020-03-02T22:12:13Z (GMT). No. of bitstreams: 4
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Previous issue date: 2019-10-31Embargo set by: Seth Robbins for item 113871
Lift date: 2022-03-02T22:12:26Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113871
Lift date: 2022-03-02T22:15:21Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113871
Lift date: 2022-03-02T22:18:25Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 113871 on 2022-03-03T10:15:13Z
Comparison of performance of shell-and-tube heat exchangers with conventional segmental baffles and continuous helical baffle
No full textProject Report on “Financial Performance Evaluation of Commercial Banks in Bangladesh”
No full textThe general objective of this study is to evaluate the financial performance of the commercial banks and the Islamic banks in context of Bangladesh. The author tries to critically compare the pros and cons across the commercial and Islamic banks in the country in this report
Representation Of Women In Parliament Of Bangladesh: Is It Hopeful?
No full textThe poor representation of women in nearly each policy-making facet of life is a universal matter. In the entire world, women are represented in government in poor ratio to their entire populace. A component of representative democracy is that irrespective of gender, all people have equal prospects to partake in the political arena. In elective points, better representation of women of power is a matter of fairness and parity. Yet, representation of women in many parliaments is often limited. Democracy cannot embellish without a rational representation of women in the parliament, which is the most influential organization of democratic states. The analytical structure of this study undertakes that the presence of women in parliament does not inevitably turn into the functional picture rather it is a result of organizational, sociological and institutional facets. This has failed to make an effective impact on the representation of women in Parliament in a particular political situation. Therefore, the issues that impede or enable women’s representation in elective points differ with the issue of socioeconomic progress, culture and the form of political arrangement. The author has taken a modest endeavor to disclose about the significant matters linked to women’s poor representation in Bangladesh Parliament
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