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Jai Verma

Bio: Jai Verma is an academic researcher from University of Notre Dame. The author has contributed to research in topics: Heterojunction & Gallium nitride. The author has an hindex of 23, co-authored 48 publications receiving 1466 citations. Previous affiliations of Jai Verma include Indian Institute of Technology Kanpur.

Papers
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TL;DR: In this paper, the authors investigate scaling properties of gate-stacks consisting of Al2O3/III-Nitride heterojunctions and find interface charges that appear closely linked to the polarization charges of the underlying nitride substrate.
Abstract: Unlike silicon and traditional III-V semiconductors, the III-nitrides exhibit high spontaneous and piezoelectric polarization charges at epitaxial polar heterojunctions. In the process of investigating scaling properties of gate-stacks consisting atomic-layer deposited Al2O3/III-Nitride heterojunctions, we find interface charges that appear closely linked to the polarization charges of the underlying nitride substrate. Through capacitance-voltage measurement on a series of samples of varying dielectric thicknesses, we find the presence and propose an origin of benign donor-type interface charges (Qit ∼6 × 1013 cm−2) at the AlN/Al2O3 junction. This interface charge is almost equal to the net polarization charge in AlN. The polarization-related dielectric/AlN interface charge and the role of oxygen in the dielectric as a possible modulation dopant potentially offer opportunities for various device applications.

154 citations

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TL;DR: In this paper, nonalloyed ohmic contacts regrown by molecular beam epitaxy were made on InAlN, AlN/AlN/GaN/SiC high-electron-mobility transistors (HEMTs).
Abstract: Nonalloyed ohmic contacts regrown by molecular beam epitaxy were made on InAlN/AlN/GaN/SiC high-electron-mobility transistors (HEMTs). Transmission-line-method measurements were carried out from 4 K to 350 K. Although the total contact resistance is dominated by the metal/ n+-GaN resistance ( ~ 0.16 Ω·mm), the resistance induced by the interface between the regrown n+ GaN and HEMT channel is found to be 0.05-0.075 Ω·mm over the entire temperature window, indicating a minimal barrier for electron flow at the as-regrown interface. The quantum contact resistance theory suggests that the interface resistance can be further reduced to be <; 0.02 Ω·mm in GaN HEMTs.

117 citations

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TL;DR: In this paper, the emission wavelength is tuned by controlling the thickness of ultrathin GaN layers with monolayer precision using plasma assisted molecular beam epitaxy, and single peaked emission spectra are achieved with narrow full width at half maximum for three different light emitting diodes operating at 232nm, 246nm, and 270nm.
Abstract: Electrically injected deep ultra-violet emission is obtained using monolayer thin GaN/AlN quantum structures as active regions. The emission wavelength is tuned by controlling the thickness of ultrathin GaN layers with monolayer precision using plasma assisted molecular beam epitaxy. Single peaked emission spectra are achieved with narrow full width at half maximum for three different light emitting diodes operating at 232 nm, 246 nm, and 270 nm. 232 nm (5.34 eV) is the shortest electroluminescence (EL) emission wavelength reported so far using GaN as the light emitting material and employing polarization-induced doping.

99 citations

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TL;DR: In this paper, an approach is proposed and experimentally demonstrated to counter the challenges of electrical carrier injection in III-Nitride heterostructures, which requires the use of wide bandgap high Al composition AlGaN active regions.
Abstract: Efficient semiconductor optical emitters in the deep-ultraviolet spectral window are encountering some of the most deep rooted problems of semiconductor physics. In III-Nitride heterostructures, obtaining short-wavelength photon emission requires the use of wide bandgap high Al composition AlGaN active regions. High conductivity electron (n-) and hole (p-) injection layers of even higher bandgaps are necessary for electrical carrier injection. This approach requires the activation of very deep dopants in very wide bandgap semiconductors, which is a difficult task. In this work, an approach is proposed and experimentally demonstrated to counter the challenges. The active region of the heterostructure light emitting diode uses ultrasmall epitaxially grown GaN quantum dots. Remarkably, the optical emission energy from GaN is pushed from 365 nm (3.4 eV, the bulk bandgap) to below 240 nm (>5.2 eV) because of extreme quantum confinement in the dots. This is possible because of the peculiar bandstructure and band alignments in the GaN/AlN system. This active region design crucially enables two further innovations for efficient carrier injection: Tunnel injection of carriers and polarization-induced p-type doping. The combination of these three advances results in major boosts in electroluminescence in deep-ultraviolet light emitting diodes and lays the groundwork for electrically pumped short-wavelength lasers.

92 citations

Journal ArticleDOI
TL;DR: The role of spontaneous and piezoelectric polarization in III-V nitride heterostructure devices is discussed in this paper, as well as opportunities in incorporating polarization in abrupt and graded heterojunctions composed of binary, ternary, and quaternary nitrides.
Abstract: The role of spontaneous and piezoelectric polarization in III-V nitride heterostructure devices is discussed. Problems as well as opportunities in incorporating polarization in abrupt and graded heterojunctions composed of binary, ternary, and quaternary nitrides are outlined.

91 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

01 Jan 2011

2,117 citations

Journal ArticleDOI
01 Jan 1977-Nature
TL;DR: Bergh and P.J.Dean as discussed by the authors proposed a light-emitting diode (LEDD) for light-aware Diodes, which was shown to have promising performance.
Abstract: Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

1,560 citations

Journal ArticleDOI
TL;DR: In this article, a mathematical framework to evaluate the performance of FETs and describe the challenges for improving the performances of short-channel FET in relation to the properties of 2D materials, including graphene, transition metal dichalcogenides, phosphorene and silicene.
Abstract: In the quest for higher performance, the dimensions of field-effect transistors (FETs) continue to decrease. However, the reduction in size of FETs comprising 3D semiconductors is limited by the rate at which heat, generated from static power, is dissipated. The increase in static power and the leakage of current between the source and drain electrodes that causes this increase, are referred to as short-channel effects. In FETs with channels made from 2D semiconductors, leakage current is almost eliminated because all electrons are confined in atomically thin channels and, hence, are uniformly influenced by the gate voltage. In this Review, we provide a mathematical framework to evaluate the performance of FETs and describe the challenges for improving the performances of short-channel FETs in relation to the properties of 2D materials, including graphene, transition metal dichalcogenides, phosphorene and silicene. We also describe tunnelling FETs that possess extremely low-power switching behaviour and explain how they can be realized using heterostructures of 2D semiconductors. Field-effect transistors (FETs) with semiconducting channels made from 2D materials are known to have fewer problems with short-channel effects than devices comprising 3D semiconductors. In this Review, a mathematical framework to evaluate the performance of FETs is outlined with a focus on the properties of 2D materials, such as graphene, transition metal dichalcogenides, phosphorene and silicene.

983 citations

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TL;DR: This collection of GaN technology developments is not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve.
Abstract: Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

788 citations