ABDULLAH ALHASSAN - Academia.edu (original) (raw)

Papers by ABDULLAH ALHASSAN

arXiv (Cornell University), May 6, 2019

III-Nitride light emitting diodes (LEDs) are the backbone of ubiquitous lighting and display appl... more III-Nitride light emitting diodes (LEDs) are the backbone of ubiquitous lighting and display applications. Imparting directional emission is an essential requirement for many LED implementations. Although optical packaging 1 , nano-patterning 2,3 and surface roughening 4 techniques can enhance LED extraction, directing the emitted light requires bulky optical components. Optical metasurfaces provide precise control over transmitted and reflected waveforms, suggesting a new route for directing light emission. However, it is difficult to adapt metasurface concepts for incoherent light emission, due to the lack of a phase-locking incident wave. In this Letter, we demonstrate metasurface-based design of InGaN/GaN quantum-well structures that generate narrow, unidirectional transmission and emission lobes at arbitrary engineered angles. We show that the directions and polarization of emission differ significantly from transmission, in agreement with an analytical Local Density of Optical States (LDOS) model. The results presented in this Letter open a new paradigm for exploiting metasurface functionality in light emitting devices. Light emitting diodes (LED) are rapidly enabling solid-state solutions to commercial lighting applications. Imparting unidirectionality to LEDs is a challenging, problem with a host of applications 5-7 awaiting a scalable solution. Directional emission is naturally observed in lasing systems, 13,14 where all of the resonators are emitting coherently. By modifying the local density

International Journal of Sustainable Development & World Ecology

This paper describes a preliminary work of developing InGaN based red LED using two-flow MOCVD re... more This paper describes a preliminary work of developing InGaN based red LED using two-flow MOCVD reactor, focussing on characteristics of the LED epiwafer from the aspects of optics, surface and crystalline structure. The active region multiquantum wells (MQWs) of the LED consists of In0.3Ga0.7N quantum well and GaN quantum barrier, which were alternatively grown for a period of 4 with Al0.28Ga0.72N as a cap layer between the quantum well and the quantum barrier. From EL measurement, the LED showed a broad emission peak at 615 nm. The broad emission can be related to the presence of hexagonal pits on the LED’s surface, as witnessed through SEM and AFM measurements. Despite of that, XRD measurement implied the LED has a relatively good crystalline structure with FWHM of ~234 arcsec in (002) and (102) scans. XRD-RSM measurement suggests that the MQWs are under strain. On the basis of this work, further effort on reducing the hexagonal pits is required to improve the characteristics of t...

Conference on Lasers and Electro-Optics, 2020

We present a metalens design made from GaN nanopillars with embedded quantum-well emitters. We fa... more We present a metalens design made from GaN nanopillars with embedded quantum-well emitters. We fabricate, using nanolithography, metalenses with different focal lengths and observe that the proposed design can effectively focus the emitted photoluminescence.

Minerals, 2021

In this study, the ion concentrations (K+, Na+, Ca2+, Mg2+, Cl−, SO42−, Br−, NO3−, and B3+) and b... more In this study, the ion concentrations (K+, Na+, Ca2+, Mg2+, Cl−, SO42−, Br−, NO3−, and B3+) and boron isotope compositions (δ11B) of 34 halite and brines samples from the Neoproterozoic Salt Range Formation, Punjab, Pakistan were studied. Relation among B3+ vs. Mg2+, B3+ vs. SO42−, δ11B vs. B3+, and δ11B vs K+ were observed, they indicated that these elements originate from multiple sources and the end members were identified as seawater, B desorption from clays, and meteoric precipitation. Halite samples of the area under study displayed a Na-HCO3-type to Ca-Cl type sedimentary basin of deposition, on δ11B vs. 1/B plot. Molar ratios of B/Cl vs. δ11B revealed the addition of B in some of the studied samples from desorption of clay minerals. This type of diagenetic desorption of B from clays is the consequence of a stress driven mechanism, generated in the proximity of a decollement zone. Results confirm that the number of B stable isotopes that fractionate between the brine and the ...

Light: Science & Applications, 2021

A MXene-GaN-MXene based multiple quantum well photodetector was prepared on patterned sapphire su... more A MXene-GaN-MXene based multiple quantum well photodetector was prepared on patterned sapphire substrate by facile drop casting. The use of MXene electrodes improves the responsivity and reduces dark current, compared with traditional Metal-Semiconductor-Metal (MSM) photodetectors using Cr/Au electrodes. Dark current of the device using MXene-GaN van der Waals junctions is reduced by three orders of magnitude and its noise spectral intensity shows distinct improvement compared with the traditional Cr/Au–GaN–Cr/Au MSM photodetector. The improved device performance is attributed to low-defect MXene-GaN van der Waals interfaces. Thanks to the high quality MXene-GaN interfaces, it is possible to verify that the patterned substrate can locally improve both light extraction and photocurrent collection. The measured responsivity and specific detectivity reach as high as 64.6 A/W and 1.93 × 1012 Jones, respectively, making it a potential candidate for underwater optical detection and commun...

Nature Photonics, 2020

Cureus, 2020

Background Diabetes mellitus is a major disease worldwide. In Saudi Arabia, it is considered to b... more Background Diabetes mellitus is a major disease worldwide. In Saudi Arabia, it is considered to be the most common disease in the country. Diabetes mellitus has been also found to be associated with 25(OH)D (vitamin D) deficiency. In Saudi Arabia, sunlight is considered a major source for vitamin D. Saudi Arabia is popular for sunny weather most of the year, in which people can get vitamin D from the sun. However, vitamin D deficiency is common in Saudi Arabia, and its deficiency can increase blood glucose levels. We conducted a study to determine the reason for vitamin D deficiency in Saudi Arabia and to assess the relationship of diabetes mellitus with vitamin D. Aim of the work This study is aimed to assess the incidence of vitamin D deficiency in non-diabetic and type II diabetic patients in the King Faisal University (KFU) Health Center in the Al-Ahsa region. Methods Open Access Original Article

Remote Sensing, 2020

Evapotranspiration (ET) is dynamic and influences water resource distribution. Sustainable manage... more Evapotranspiration (ET) is dynamic and influences water resource distribution. Sustainable management of water resources requires accurate estimations of the individual components that result in evapotranspiration, including the daily net radiation (DNR). Daily ET is more useful than the evaporative fraction (EF) provided by remote sensing ET models, and to account for daily variations, EF is usually combined with the DNR. DNR exhibits diurnal and spatiotemporal variations due to landscape heterogeneity. In the modified Two-Source Energy Balance (TSEB) approach by Zhuang and Wu, 2015, ecophysiological constraint functions of temperature and moisture of plants based on atmospheric moisture and vegetation indices were introduced, but the DNR was not spatially accounted for in the estimation of the daily ET. This research adopted a novel approach that accounts for spatiotemporal variations in estimated daily ET by incorporating the Bisht and Bras DNR model in the modified version of th...

Applied Physics Express, 2017

An improvement in the suppression of surface riding of magnesium from p-GaN:Mg into subsequent la... more An improvement in the suppression of surface riding of magnesium from p-GaN:Mg into subsequent layers was achieved via low temperature flow modulation epitaxy. In particular, the slope of the Mg concentration drop was reduced to 5 nm/dec for a growth temperature of 620°Cthe lowest value ever reported for metalorganic chemical vapor deposition. The electrical quality of the top layer was verified by creating a two-dimensional electron gas on top of the buried p-GaN layer, which exhibited a mobility of 1300 cm 2 V %1 s %1. In addition, layers grown using flow modulation epitaxy were shown to block the propagation of Mg more efficiently than samples in which an ex situ wet etch was used.

MOJ Orthopedics & Rheumatology, 2019

The aim of this study is to retrospectively review the patients admitted and treated in King Fahd... more The aim of this study is to retrospectively review the patients admitted and treated in King Fahd Hofuf Hospital, in alhasa, Saudi Arabia for an ACL tear reconstruction over a 5-year period and document the meniscal involvement Patients We searched our hospital database between January 2011 and December 2016 and evaluated the patient's records with the diagnosis of ACL tear.

Policy Papers, 2013

In November 2011, the G-20 endorsed an action plan to support the development of local currency b... more In November 2011, the G-20 endorsed an action plan to support the development of local currency bond markets (LCBM). International institutions—the IMF, the World Bank, the EBRD, and the OECD—were asked to draw on their experience to develop a diagnostic framework (DF) to identify general preconditions, key components, and constraints for successful LCBM development. The objective is to provide a tool for analyzing the state of development and efficiency of local currency bond markets. The application of the DF is expected to be flexible, bearing in mind that the potential for LCBM development depends on economic size, financing needs, and stage of economic development.

ACS Applied Energy Materials, 2018

Indium gallium nitride (InGaN) is an attractive semiconductor, with a tunable direct bandgap for ... more Indium gallium nitride (InGaN) is an attractive semiconductor, with a tunable direct bandgap for photoelectrochemical water splitting, but it corrodes in aqueous electrolytes. Cobalt oxide (CoOx) is a promising co-catalyst to protect photoelectrodes and to accelerate the charge transfer. CoOx is earth-abundant and stable in extremely alkaline conditions and shows high activity for the oxygen evolution reaction (OER). In this work, we demonstrate that CoOx directly deposited onto InGaN/GaN multiple quantum wells photoanodes exhibits excellent activity and stability in a strong alkaline electrolyte, 1M NaOH (pH=13.7), for water oxidation up to 28 hours, while a reference sample without the catalyst degraded rapidly in the alkaline electrolyte. Under simulated solar illumination, the CoOx-modified InGaN/GaN quantum well photoanode showed a high photocurrent density of 1.26 mA cm-2 at 1.23 V and an onset potential of-0.03 V versus a reversible hydrogen electrode.

ACS applied materials & interfaces, Jan 18, 2017

We demonstrate efficient semipolar (11-22) 550 nm yellow/green InGaN light-emitting diodes (LEDs)... more We demonstrate efficient semipolar (11-22) 550 nm yellow/green InGaN light-emitting diodes (LEDs) with In0.03Ga0.97N barriers on low defect density (11-22) GaN/patterned sapphire templates. The In0.03Ga0.97N barriers were clearly identified, and no InGaN clusters were observed by atom probe tomography measurements. The semipolar (11-22) 550 nm InGaN LEDs (0.1 mm2 size) show an output power of 2.4 mW at 100 mA and a peak external quantum efficiency of 1.3% with a low efficiency drop. In addition, the LEDs exhibit a small blue-shift of only 11 nm as injection current increases from 5 to 100 mA. These results suggest the potential to produce high efficiency semipolar InGaN LEDs with long emission wavelength on large-area sapphire substrates with economical feasibility.

IMF Working Papers, 2007

This Working Paper should not be reported as representing the views of the IMF. The views express... more This Working Paper should not be reported as representing the views of the IMF. The views expressed in this Working Paper are those of the author(s) and do not necessarily represent those of the IMF or IMF policy. Working Papers describe research in progress by the author(s) and are published to elicit comments and to further debate. This paper documents the phenomenon of underpricing initial public offerings (IPOs) for 47 firms that went public between 2001 and 2006 in the equity markets of the six Gulf Cooperation Council (GCC) countries. The average initial abnormal returns of 290 percent exceed those found in the existing literature for both developed and emerging markets IPOs. Although the IPOs' returns over the one-year horizon beat the market index benchmark, they present negative abnormal returns once initial returns are excluded, which is consistent with findings in other industrial and emerging markets. The empirical models reject the hypothesis that the IPOs' performance is driven by the common independent variables employed in the literature. On the contrary, in the case of the GCC, country-and industry-specific characteristics, in addition to the timing of the offers, play key roles in explaining the abnormal returns of IPOs. This paper's empirical findings support the hypothesis that investors initially tend to be over-optimistic about the performance of IPOs, but grow more pessimistic over time.

Asian Research Journal of Arts & Social Sciences, 2016

Female head porters, a category of street children in Kumasi, Ghana, face numerous challenges whi... more Female head porters, a category of street children in Kumasi, Ghana, face numerous challenges while working and living on the streets. Yet, very few research has been done to ensure that this section of the disadvantaged population have better lives on and beyond those of the streets. Most studies with this population have focused on their troubles, with little done on the ways to help them improve upon or change their conditions. Focusing on female head porters receiving services from a non-governmental organisation in Kumasi, this study aimed to explore the perceptions of the female head porters on their social support and how that helped them cope with life on and beyond the streets. Semi-structured in-depth interviews were conducted with 25 female head porters in Kumasi with the help of an interview guide, for a period of four weeks. Thematic analysis

Asian Research Journal of Arts & Social Sciences, 2017

Persons with disabilities constitute a significant proportion of the minority population in Sekon... more Persons with disabilities constitute a significant proportion of the minority population in Sekondi, Ghana. Yet, they are the most neglected and existing programs do not meet their needs. Consequently, this study aimed to understand the perception of persons without disabilities towards individuals with disabilities in Sekondi and to explore the attitudes of the general public towards disability. Semi-structured interviews were conducted with 17 persons with disabilities and 25 persons without disabilities over an eight-week period. Persons with disabilities were individuals receiving services from the Department of Social Welfare in Sekondi. Thematic analysis was used to analysed data from the interviews. The study revealed that the participants without disabilities viewed disability as a disease and a punishment from God or the gods. Yet, they indicated that they showed compassion and love towards persons with disabilities. However, most persons with disabilities disagreed to this while a few argued that they were shown love by their typical peers. 2 Also, both persons with and without disabilities stated that having the experience with care for persons with disabilities and being a female are features which meant the individual is likely to develop positive attitude towards persons with disabilities. It has been suggested that training should be given to people with the experience and more women caring for persons with disabilities in Ghana as these women are more likely to provide adequate care and protection for individuals with disabilities. Finally, policies and programs for persons with disabilities in Sekondi should consider recommendations to promote the wellbeing of persons with disabilities.

Sovereign Wealth FundsThe New Intersection of Money and Politics, 2012

IMF Working Papers, 2010

This Working Paper should not be reported as representing the views of the IMF.