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Quantum well engineering of InAlAs/InGaAs HEMTs for low impact ionization applications
Umesh P. Gomes,Yiqiao Chen,Sanjib Kabi,Peter Chow,Dhrubes Biswas 한국물리학회 2013 Current Applied Physics Vol.13 No.3
The performance of InAlAs/InGaAs quantum well field effect transistors are subject to high impact ionization and band-to-band tunneling (BTBT) due to its narrow bandgap feature. In this work, the energy gap is engineered using strain and quantization techniques to increase the effective energy gap leading to low impact ionization and BTBT leakage current. It is shown that the impact ionization is reduced in 5 nm channel device as compared to 13 nm device with onset at approximately Egeff/q. Also the band-to-band-tunneling current is reduced due to the increase in effective energy gap. We have also investigated the effects of quantum well engineering on the dc performance of InGaAs HEMTs.
Lee, Sung Keun,Lin, Jung-Fu,Cai, Yong Q,Hiraoka, Nozomu,Eng, Peter J,Okuchi, Takuo,Mao, Ho-Kwang,Meng, Yue,Hu, Michael Y,Chow, Paul,Shu, Jinfu,Li, Baosheng,Fukui, Hiroshi,Lee, Bum Han,Kim, Hyun Na,Yoo National Academy of Sciences 2008 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.105 No.23
<P>Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; 3O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the Earth's lower mantle.</P>
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°.
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.