Author
Oliver Ambacher
Other affiliations: Osram, Siemens, Cornell University ...read more
Bio: Oliver Ambacher is an academic researcher from Fraunhofer Society. The author has contributed to research in topics: Amplifier & High-electron-mobility transistor. The author has an hindex of 64, co-authored 848 publications receiving 26256 citations. Previous affiliations of Oliver Ambacher include Osram & Siemens.
Papers published on a yearly basis
Papers
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24 Mar 2020
TL;DR: In this paper, a lateral GaN-on-Si power IC is presented, which realizes the core functionality for power converters on-chip, and demonstrates significant functionality enhancement of large-area GaN power transistors by monolithic integration of additional circuitry.
Abstract: A lateral GaN-on-Si power IC is presented, which realizes the core functionality for power converters on-chip. Monolithic integration enhances the functionality of a 600 V, 85mW power transistor by an intrinsic freewheeling diode, gate-driver, current shunt and an isolated temperature sensor. An integrated auxiliary transistor and a diode realize a single-input pre-driver, a current-mirror sensor or a voltage clamp for on-resistance measurement. Gate driver losses were measured up to 70 MHz. A 350V hard-switching half-bridge shows 98.8% efficiency at 600W and 65 kHz. Continuous 40MHz resonant-switching at 200V and 6A triangular peak current was achieved, operating the half-bridge at 50% duty-cycle with a 75 nH air-core inductor. The work demonstrates significant functionality enhancement of large-area GaN power transistors by monolithic integration of additional circuitry at low additional cost and chip area.
5 citations
01 Jan 2003
TL;DR: In this article, the thickness of the altered layer created by ion bombardment of the 6H silicon carbide single crystal was determined by means of Auger depth proling combined with factor analysis.
Abstract: The thickness of the altered layer created by ion bombardment of the 6H silicon carbide single crystal was determined by means of Auger depth proling combined with factor analysis. After pre-bombardment of the surface until the steady state by argon ions with energies 1, 2 and 4 keV, the micro proles of the altered layers were recorded by sputtering with low energy argon ions of 300 eV. As the position and shape of the carbon Auger signal depend on the perfection of the crystalline structure, they were used for depth prole evaluation by factor analysis. In this way the depth proles of the damaged surface region could be estimated in dependence on the ion energy. The thickness of the altered layer of SiC bombarded with keV Ar ions using an incident angle of 80 was obtained. K e y w o r d s: sputtering, altered layer, AES, depth proling, implantation, silicon carbide, factor analysis Various steps in device technology as well as a number of surface sensitive analytical techniques often employ sputtering of the surfaces under study by ions. A surface sensitive analytical technique like Auger electron spectroscopy (AES) in combination with low energy ion sputtering is a valuable tool for high resolution depth proling. However, sputtering of the surface by energy ions often brings about changes in morphology, structure an composition of the subsurface region, giving rise to an altered layer with characteristics dieren t from those of the bulk. The thickness of the altered layer and its properties depend on the ion beam parameters (energy, ion species, angle of incidence) as well as on the investigated material itself. AES is a well suited method for investigations of the sputter induced compositional micro proles close to the surface [1] and for thickness determination of the altered layer. One of the methods how to investigate the properties of such altered layers is sputter depth proling of the altered layer under conditions of very shallow ion damage, ie, with a grazing incidence angle and/or with a use of low energy ions (some hundreds of eV) [2]. The present paper reports on investigations of the altered layers of SiC single crystal surfaces due to ion bombardment. Compositional changes at the silicon carbide surface caused by low energy ion bombardment are not well understood up to date. Publications with very different results can be found in the literature reporting on preferential sputtering and accompanying surface compositional changes of the SiC surface. Surface enrichment in silicon [3, 4, 5], restored stoichiometry [6, 7] and also carbon enriched surfaces [8, 9] after sputtering with argon were reported. These discrepancies strongly motivate evaluation of the measured data in order to get a detailed picture of the silicon carbide surface after sputtering.
5 citations
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TL;DR: In this paper, a simple growth model was suggested to explain the formation of domain boundaries and stacking faults formed during the coalescence of thin InN epilayers by means of electron microscopy and X-ray diffraction.
5 citations
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TL;DR: In this article, the ESR signature of the deep defect appears for excitation energies > 2.6 eV and saturates above 2.7 eV in GaN and Al x Ga 1-x N alloys.
Abstract: Electron Spin Resonance (ESR) and related methods have been used to study defects in GaN and in Al x Ga 1-x N ternary alloys. In particular, Light-induced ESR of a thick MOCVD grown layer of GaN shows that the ESR signature of the deep defect appears for excitation energies > 2.6 eV and saturates above 2.7 eV. This information provides a direct measure of the energetic level position of the diamagnetic to paramagnetic transition of this center. Furthermore, standard ESR investigations of MBE-grown layers of Al x Ga 1-x N alloys were performed with emphasis on the effective-mass donor resonance. Composition and temperature-dependent measurements of the resonance position are presented.
5 citations
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06 Jul 2014TL;DR: In this article, the authors demonstrate a system with one to three carriers near 237 GHz for (75...100) Gbit/s single-polarization transmission over distances of (20...40) m.
Abstract: High carrier frequencies in the terahertz range 0.1...30 THz are required for wireless data transmission at line rates at or beyond 100 Gbit/s. Here we demonstrate a system with one to three carriers near 237 GHz for (75...100) Gbit/s single-polarization transmission over distances of (20...40) m. The narrow-band THz carrier is generated by photomixing of highly stable mode-locked laser lines in a uni-travelling-carrier photodiode. The electrical photodiode output is radiated over a lensed horn antenna. Besides a receiving lensed horn antenna, the receiver comprises monolithic integrated circuits with mixers and amplifiers. This synergetic use of THz photonics and electronics (“teratronics”) should be scalable to wireless Tbit/s transmission over 1 km. Such a wireless link could bridge the last mile to a subscriber, or could connect two spatially separated fibre gateways.
5 citations
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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
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TL;DR: The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or her own research.
Abstract: I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or
7,563 citations
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TL;DR: In this paper, the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method, is reviewed.
Abstract: This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.
6,917 citations
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TL;DR: In this article, the authors present a comprehensive, up-to-date compilation of band parameters for the technologically important III-V zinc blende and wurtzite compound semiconductors.
Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.
6,349 citations
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TL;DR: This review gives a general introduction to the materials, production techniques, working principles, critical parameters, and stability of the organic solar cells, and discusses the alternative approaches such as polymer/polymer solar cells and organic/inorganic hybrid solar cells.
Abstract: The need to develop inexpensive renewable energy sources stimulates scientific research for efficient, low-cost photovoltaic devices.1 The organic, polymer-based photovoltaic elements have introduced at least the potential of obtaining cheap and easy methods to produce energy from light.2 The possibility of chemically manipulating the material properties of polymers (plastics) combined with a variety of easy and cheap processing techniques has made polymer-based materials present in almost every aspect of modern society.3 Organic semiconductors have several advantages: (a) lowcost synthesis, and (b) easy manufacture of thin film devices by vacuum evaporation/sublimation or solution cast or printing technologies. Furthermore, organic semiconductor thin films may show high absorption coefficients4 exceeding 105 cm-1, which makes them good chromophores for optoelectronic applications. The electronic band gap of organic semiconductors can be engineered by chemical synthesis for simple color changing of light emitting diodes (LEDs).5 Charge carrier mobilities as high as 10 cm2/V‚s6 made them competitive with amorphous silicon.7 This review is organized as follows. In the first part, we will give a general introduction to the materials, production techniques, working principles, critical parameters, and stability of the organic solar cells. In the second part, we will focus on conjugated polymer/fullerene bulk heterojunction solar cells, mainly on polyphenylenevinylene (PPV) derivatives/(1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61) (PCBM) fullerene derivatives and poly(3-hexylthiophene) (P3HT)/PCBM systems. In the third part, we will discuss the alternative approaches such as polymer/polymer solar cells and organic/inorganic hybrid solar cells. In the fourth part, we will suggest possible routes for further improvements and finish with some conclusions. The different papers mentioned in the text have been chosen for didactical purposes and cannot reflect the chronology of the research field nor have a claim of completeness. The further interested reader is referred to the vast amount of quality papers published in this field during the past decade.
6,059 citations