Defect Characterization of 4H-SIC by Deep Level Transient Spectroscopy (DLTS) and Influence of Defects on Device Performance

Silicon carbide (SiC) is one of the key materials for high power opto-electronic devices due to its superior material properties over conventional semiconductors (e.g., Si, Ge, GaAs, etc). SiC is also very stable and a highly suitable material for radiation detection at room temperature and above. The availability of detector grade single crystalline bulk SiC is limited by the existing crystal growth techniques which introduce extended and microscopic crystallographic defects during the growth process. Recently, SiC based high-resolution semiconductor detectors for ionizing radiation have attracted world-wide attention due to the availability of high resistive, highly crystalline epitaxial layers with very low micropipe defect content (\u3c 1 cm-2). SiC Schottky barrier radiation detectors on epitaxial layers can be operated with a high signal-to-noise ratio even above room temperature due to its wide band-gap. However, significant amount of intrinsic defects and impurities still exist in the grown SiC epilayer which may act as traps or recombination/generation centers and can lead to increased leakage current, poor carrier lifetime, and reduced carrier mobility. Unfortunately, the nature of these electrically active deep levels and their behavior are not well understood. Therefore, it is extremely important to identify these electrically active defects present in the grown epitaxial layers and to understand how they affect the detector performance in terms of leakage current and energy resolution. In this work, Schottky barrier radiation detectors were fabricated on high quality n-type 4H-SiC epitaxial layers. The epitaxial layers were grown on nitrogen doped n-type 4H-SiC (0001) substrates by a hot wall chemical vapor deposition (CVD) process. The epitaxial growth was carried out with 8o off-cut towards the [112̅0] direction. The Schottky barriers were formed on the epitaxial layers (Si-face) by depositing thin (~10 nm) circular Ni contact (area ~10 mm2) which acts as the detector window. The thickness of the detector window was decided such that there was minimal alpha energy attenuation while maintaining a reliable electrical contact. For the back contact, ~100 nm thick square (~40 mm2) Ni contact was deposited on the C-face of the 4H-SiC substrate. The junction properties of the fabricated Schottky barrier radiation detectors were characterized through current-voltage (I-V) and capacitance-voltage (C-V) measurements. From the fabricated devices, those with high barrier height (~ 1.6 eV) and extremely low leakage current (few pA at a reverse bias of ~ -100 V) were selected for alpha spectroscopic measurements. Alpha pulse-height spectra was obtained from the charge pulses produced by the detector irradiated with a standard 0.1 μCi 241Am source. The charge transport and collection efficiency results, obtained from the alpha particle pulse-height spectroscopy, were interpreted using a drift-diffusion charge transport model. The detector performances were evaluated in terms of the energy resolution. From alpha spectroscopy measurements the FWHM (full width at half maxima) of the fabricated Schottky barrier detectors were in the range of 0.29% - 1.8% for the main alpha peak of 241Am (5.486 MeV). Deep level transient spectroscopy (DLTS) studies were conducted in the temperature range of 80 K - 800 K to identify and characterize the electrically active defects present in the epitaxial layers. Deep level defect parameters (i.e. activation energy, capture cross-section, and density) were calculated from the Arrhenius plots which were obtained from the DLTS spectra at different rate windows. The observed defects in various epitaxial layers were identified and compared with the literature. In the 50 μm epitaxial layer, a new defect level located at Ec - 2.4 eV was observed for the first time. The differences in the performance of different detectors were correlated on the basis of the barrier properties and the deep level defect types, concentrations, and capture cross-sections. It was found that detectors, fabricated on similar wafers, can perform in a substantially different manner depending on the defect types. For 20 μm epitaxial layer Schottky barrier radiation detectors, deep levels Z1/2 (located at ~ Ec - 0.6 eV) and EH6/7 (located at ~ Ec - 1.6 eV) are related to carbon vacancies and their complexes which mostly affect the detector resolution. For 50 μm epitaxial layer Schottky barrier radiation detectors, Z1/2, EH5, and the newly identified defect located at Ec - 2.4 eV mostly affect the detector resolution. The annealing behavior of deep level defects was thoroughly investigated by systematic C-DLTS measurements before and after isochronal annealing in the temperature range of 100 ˚C - 800 ˚C. Defect parameters were calculated after each isochronal annealing. Capture cross-sections and densities for all the defects were investigated to analyze the impact of annealing. The capture cross-sections of the defects Ti (c) (located at Ec ˗ 0.17 eV) and EH5 (located at Ec ˗ 1.03 eV) were observed to decrease with annealing temperature while the densities did not change significantly. Deep level defects Z1/2 and EH6/7 were found to be stable up to the annealing temperature of 800 ˚C

Covid-19 infection; loss of taste, smell, and neurogenic respiratory failure

Neurological Signs and Symptoms in COVID-19: Like the rest of the world, Pakistan is been gripped by unprecedented and complex burden of COVID-19. While the diseases got upgraded to a pandemic, the preparedness of even the first world countries to combat COVID-19 is distressing, as there seems to be a lack of clear strategy to tackle the disease spread and treatment

On Food and Nutrition Policy Activities in the USA, Australia, and Norway

Formulation and implementation of a national food and nutrition policy is important for ensuring good health and quality of life. This study examined the formulation and implementation of food and nutrition policies in the USA, Australia, and Norway. Library searches, MEDLINE and POPLINE searches, and personal communications were used for collecting information and data on nutrition activities and policy formulation and implementation in each country. These countries were selected because policy activities have been ongoing since the 1930s with a clear improvement in the nutritional status of the people. Multisectoral participation, conflicts of interest, strategies to alter diet, and attempts to deal with new problems have been highlighted and compared. Findings of the study may be useful to policy-makers in less-developed countries during future policy-making processes

Neurological manifestations of COVID-19

Coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) has turned out to be a formidable pandemic. Upcoming evidence from confirmed cases of COVID-19 suggests an anticipated incursion of patients with neurological manifestations in the weeks to come. An expression of the angiotensin-converting enzyme 2 (ACE 2), the cellular receptor for SARS-CoV-2 over the glial cells and neurons have made the brain a potential target. Neurotoxicity may occur as a result of direct, indirect and post-infectious complications. Attention to neurological deficits in COVID-19 is fundamental to ensure appropriate, timely, beneficial management of the affected patients. Most common neurological manifestations seen include dizziness, headache, impaired consciousness, acute cerebrovascular disease, ataxia, and seizures. Anosmia and ageusia have recently been hinted as significant early symptoms in COVID-19. As cases with neurological deficits in COVID-19 emerge, the overall prognosis is yet unknown

Non performing loans - its causes, consequences and some learning

Investment in productive sector is the precondition for achieving the economic growth from a country perspective. Capital formation positively supports this investment function. Once a satisfactory level of capital is formed, the option of sound investment comes that ultimately leads to flow additional capital in future. The financial institutions, mainly banks, do these functions. In countries like ours, investment leakage in the form of non-functionalities poses a great threat on the sound running of this ‘capital formation – investment – capital formation’ process. This paper deals with non performing loan situations, basically the causes and consequences of this economic devil that is very much embedded in current economic structure. The possible steps are also pointed out to handle such situation.capital formation, workout, LRA, recovery agency

The Performance of Ultrafine Palm Oil Fuel Ash in Suppressing the Alkali Silica Reaction in Mortar Bar

This study evaluates the effect of ultrafine palm oil fuel ash (POFA) on the alkali silica reaction (ASR) of mortar. To study the effectiveness of ultrafine POFA in suppressing the ASR, four different sizes of POFA were used in this study: the unground (UG), medium (MP), fine (FP), and ultrafine size (UF). Characterization of POFA was done to investigate their particle size, fineness, specific gravity, chemical composition, loss on ignition (LOI), and morphology. Initially, the pessimum effect of the sandstone aggregate was determined by blending 5, 15, 50, 75, and 100% of sandstone aggregates with the granite. POFA was then introduced as cement replacement at 0 - 40% by weight of binder. To investigate the effect of ultrafine POFA on ASR, ASTM C1260 and ASTM C1567 were adopted. The strength activity index was also determined to study the pozzolanic effect of the ultrafine POFA. Results show that the ultrafine POFA significantly increase the pozzolanic reactivity of mortar. At 14-days of testing, ultrafine POFA shows higher resistance against the alkali silica reaction (ASR) attack compared to coarser POFA. Higher level of replacement is required for coarser POFA to resist ASR attack in the mortar bar

Compressive Strength Development of Dune Sand Reactive Powder Concrete (RPC) Under Different Curing Conditions

Reactive powder concrete (RPC) is a special type of concrete with remarkable properties, particularly compressive strength. Some of its main disadvantages include its high cement and SF content, fine quartz with a preferred size of 150 µm - 600 µm, and low water-tobinder ratio. These characteristics increase the cost of RPC production and affect sustainable development. Because of this, researchers have resorted to exploring substitutes to cement and quartz to produce an eco-friendlier type of RPC. Accordingly, this research aims to study the compressive strength development of RPC prepared with dune sand and supplementary cementitious materials (SCM). Three main factors were investigated including 1) replacing cement with 30% ground granulated blast furnace slag (GGBS), 2) using ternary blends of GGBS and fly ash (FA) in RPC, and 3) applying 100ᵒC hot air curing (HAC) to RPC. Overall, the results showed that the compressive strength of HAC and water cured specimens exceeded 120 MPa after 12 hours and 28 days, respectively. Moreover, the compressive strength development of the mixes incorporating SCM was slower than that of the control mix incorporating cement only under HAC conditions

Impact of Lymphatic Filariasis (LF) on Hemoglobin Content and Anemia: A Cross-Sectional Based Study

Lymphatic filariasis (LF) is a vector-borne chronically disabling parasitic infection causing elephantiasis, lymphedema, and hydrocele. The infection is endemic in 83 countries worldwide, with more than 1.2 billion people at risk and 120 million already infected. LF is caused by thread-like adult parasitic worms, which live in the human lymphatic system and causes swelling of the scrotum, male genitalia, breast and limbs. It is caused by tissue-dwelling nematode worms belonging to the order “Filariidea” which is transmitted to man by the infective bites of blood sucking mosquitoes. About 90% of these infections are caused by Wuchereria bancrofti.  There are limited number of reports available describing the presence of microfilaria in bone marrow. There is a report a young patient who developed aplastic anemia following varicella infection, and peripheral blood and bone marrow showed many microfilariae of Wuchereria bancrofti. This experiment was designed to assess hemoglobin content by sex; and anemic condition by age and sex among 119 case respondents and 102 controls.  Hemoglobin level was found to be a bit better among case respondents than controls. By sex, hemoglobin level was better among males than females in both case respondents and control groups. Among case respondents 6-59 months age male group and 5-9 years age female group was found anemic. But in control group all the male respondents in all age groups and only one female in 5-9 years age group were found anemic. Keywords: Hemoglobin, Anemia and Lymphatic Filariasis

Hygiene Practices in the Restaurants of Dhaka North City Corporation, Bangladesh

Food safety in food establishments has been considered a global and increasing public health concern in developing countries like Bangladesh. Poor personal and environmental hygiene contributes to food contamination and results in food-borne diseases. This report represents the current hygienic state of middle-scale restaurants of Dhaka North City Corporation in Bangladesh. This study examines the prevailing environment, cleanliness, and hygiene practices of the randomly selected restaurants through on-site visiting. It was a cross-sectional observational study where a total of 134 restaurants were observed by taking the consent of the owner. The data were collected by a structured checklist where variables were categorized as acceptable, moderately acceptable, and unacceptable that denoting whether the restaurants perform all the hygiene practices properly or operate unhygienic activities on daily basis.  However, the study revealed that most restaurants did not follow food hygiene practices whereas 12.7 % of restaurants were located beside unhygienic places, and 79.9 % didn’t have toilet facilities. Nevertheless, the practices of food handlers were also very alarming because most of them did not follow proper dress codes while distributing food among customers. Overall, the study explored that only 9% of restaurants conduct healthy practices whereas 46.3% carried out both healthy and unhealthy practices and 44.7% operate mostly unhygienic practices. Therefore, the study findings will assist the policy makers and planners in designing interventions to improve the sanitary conditions of food establishments and aware the consumer as well. Keywords: Food, Hygiene Practices, Restaurants of Dhaka North City Corporation, Bangladesh. DOI: 10.7176/FSQM/119-05 Publication date:September 30th 202