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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°.
Ankush Bag,Rahul Kumar,Partha Mukhopadhyay,Mihir K. Mahata,Apurba Chakraborty,Saptarsi Ghosh,Sanjay K. Jana,Dhrubes Biswas 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.4
In-situ RHEED and ex-situ AFM characterizations have been employed to investigate transformations of surface topography with the thickness of PAMBE grown AlGaN and InGaN on GaN. The ternary alloys have been grown with identical growth-front roughness as confirmed by XRR and RHEED observations. The spottier RHEED has been observed with increased thickness of the InGaN as opposed to streakier behavior of AlGaN. We have noticed incremental nature of RMS roughness, skewness and kurtosis of InGaN surface compared to GaN or AlGaN from AFM as evident by final spotty RHEED for InGaN. However, the analyzed fractal dimension is lower for InGaN as opposed to AlGaN ( ). From the kinetic roughening perspective of adatoms, the experimental evidences lead to the high correlation between binding energy of the cluster atoms ( ) and the modified DDA growth model with dissociation and evaporation to confirm the efficacy of the study. The initial streaky and spotty RHEED of InGaN and AlGaN, respectively, can be attributed to their Eb that causes smoothing and roughening of the GaN surface due to adatoms surface mobility behavior. Therefore, the fractal description reveals the fact during formation of nitride hetero-interface while other AFM results describe the top surface.
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.
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.