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Palash Das,Nripendra N. Halder,Rahul Kumar,Sanjay Kr. Jana,Sanjib Kabi,Boris Borisov,Amir Dabiran,Peter Chow,Dhrubes Biswas 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.6
This paper presents an approach of compositional grading of the barrier in AlGaN/GaN quantum well heterostructure to achieve high two dimensional electron gas (2DEG) carrier concentration and mobility for RF power amplifier applications. Plasma assisted Molecular Beam Epitaxy (PAMBE) has been used to grow compositionally graded AlGaN/GaN and AlGaN/AlN/GaN heterostructures. In-situ cathodoluminescence (CL) and ex-situ high resolution x-ray diffraction (HRXRD) along with high resolution transmission electron microscopy (HRTEM) techniques were used to study the compositions and thicknesses of grown heterostructures. Ohmic contact formation for all the samples were found to be challenging due to unusual surface behavior and thus addressed with three different metallization schemes. The graded AlGaN/GaN and AlGaN/AlN/GaN heterostructures show 2DEG carrier concentrations of 2.0 × 1013 cm–2 and 2.3 × 1013 cm–2 with carrier mobility of 764 cm2v–1s–1 and 960 cm2v–1s–1, respectively at room temperature. A performance index has been proposed to correlate the obtained results with its suitability for particular RF applications.
Palash Das,Sanjay Kumar Jana,Nripendra N. Halder,S. Mallik,S. S. Mahato,A. K. Panda,Peter P. Chow,Dhrubes Biswas 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.6
In this letter, a standard deviation based optimization technique has been applied on High Resolution X-ray Diff raction symmetricand asymmetric scan results to accurately determine the Aluminum molar fraction and lattice relaxation of MolecularBeam Epitaxy grown compositionally graded Aluminum Gallium Nitride (AlGaN)/Aluminum Nitride/Gallium Nitride(GaN) heterostructures. Mathews–Blakeslee critical thickness model has been applied in an alternative way to determinethe partially relaxed AlGaN epilayer thicknesses. The coupling coeffi cient determination has been presented in a diff erentperspective involving sample tilt method by off set between the asymmetric planes of GaN and AlGaN. Sample tilt is furtherincreased to determine mosaic tilt ranging between 0.01° and 0.1°.
Investigating the spatial collision factors involved in bikeshare crashes at Washington, D.C
Showmitra Kumar Sarkar,Kazi Redwan Shabab,Palash Chandra Das,Mohamed H. Zaki 대한공간정보학회 2023 Spatial Information Research Vol.31 No.1
The objective of the study is to explore and characterize the spatial collision factors for bikeshare crashes using spatial and mathematical modeling. First, the nine most influential components behind the bikeshare crashes in Washington, D.C (179 census tracts) were selected as study variables (i.e., population density, number of bikeshare trips, etc.). Next, a spatial weight matrix was used to quantify the spatial relationships among the study variables with the bikeshare crashes. Finally, three models (i.e., Classic Regression, Spatial Lag, and Spatial Error) were used to investigate the essence of the interaction between these variables and bikeshare crashes. Finally, the spatial collision factors involved in bikeshare crashes were identified. According to model results, two causal factors (i.e., no. of cafe and no. of bikeshare points) significantly influence the bikeshare crashes in the Washington, D.C. area. The findings regarding spatial factors involved in bikeshare crashes can be useful in making optimum decisions regarding planning for bikeshare safety.
Spatial modeling of COVID-19 transmission in Bangladesh
Sarkar Showmitra Kumar,Ekram Khondaker Mohammed Mohiuddin,Das Palash Chandra 대한공간정보학회 2021 Spatial Information Research Vol.29 No.5
The purpose of the research was to investigate and identify the demographic risk factors behind the transmission of COVID-19 in Bangladesh based on spatial and statistical modeling. Number of COVID-19 confirmed cases per thousand population as the dependent variable and nine demographic explanatory variables were considered. Different spatial (i.e., Spatial Lag and Spatial Error Model) and non-spatial (Classic Model) regression techniques were employed in the research to detect the geographical relevance of potential risk factors affecting the transmission of COVID-19. Results indicate that population density was crucial for explaining the pattern of COVID-19 transmission in Bangladesh. Spatial Auto-correlation suggests that the spatial pattern of population density were significantly clustered at a confidence interval of 95%. Again, the regression analysis also shows that population density is an influential determinant for the propagation of COVID-19 in Bangladesh, with densely populated districts like Dhaka and Narayanganj also being among the worst affected areas. The findings of this research will help the government agencies and communities for effective and well-informed decision making in order to develop and implement strategies to contain the further spread of COVID-19 in Bangladesh.
Reverse Bias Leakage Current Mechanism of AlGaN/InGaN/GaN Heterostructure
Apurba Chakraborty,Saptarsi Ghosh,Partha Mukhopadhyay,Sanjay K. Jana,Syed Mukulika Dinara,Ankush Bag,Mihir K. Mahata,Rahul Kumar,Subhashis Das,Palash Das,Dhrubes Biswas 대한금속·재료학회 2016 ELECTRONIC MATERIALS LETTERS Vol.12 No.2
The reverse bias leakage current mechanism of AlGaN/InGaN/GaNheterostructure is investigated by current-voltage measurement intemperature range from 298 K to 423 K. The Higher electric field acrossthe AlGaN barrier layer of AlGaN/InGaN/GaN double heterostructuredue to higher polarization charge is found to be responsible for strongFowler-Nordheim (FN) tunnelling in the electric field higher than3.66 MV/cm. For electric field less than 3.56 MV/cm, the reverse biasleakage current is also found to follow the trap assisted Frenkel-Poole(FP) emission in low negative bias region. Analysis of reverse FPemission yielded the barrier height of trap energy level of 0.34 eV withrespect to Fermi level.