Author
Joachim Würfl
Other affiliations: Technical University of Berlin, Leibniz Association
Bio: Joachim Würfl is an academic researcher from Ferdinand-Braun-Institut. The author has contributed to research in topics: High-electron-mobility transistor & Gallium nitride. The author has an hindex of 28, co-authored 160 publications receiving 2941 citations. Previous affiliations of Joachim Würfl include Technical University of Berlin & Leibniz Association.
Papers published on a yearly basis
Papers
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TL;DR: In this paper, a systematic study of GaN-based heterostructure field effect transistors with an insulating carbon-doped GaN back barrier for high-voltage operation is presented.
Abstract: A systematic study of GaN-based heterostructure field-effect transistors with an insulating carbon-doped GaN back barrier for high-voltage operation is presented. The impact of variations of carbon doping concentration, GaN channel thickness, and substrates is evaluated. Tradeoff considerations in on-state resistance versus current collapse are addressed. Suppression of the off-state subthreshold drain-leakage currents enables a breakdown voltage enhancement of over 1000 V with a low on-state resistance. Devices with a 5-μm gate-drain separation on semi-insulating SiC and a 7-μm gate-drain separation on n-SiC exhibit 938 V and 0.39 mΩ·cm2 and 942 V and 0.39 m Ω·cmcm2, respectively. A power device figure of merit of ~ 2.3 × 109 V2/Ω·cm2 was calculated for these devices.
191 citations
TL;DR: In this article, a GaN-based heterostructure lateral Schottky barrier diodes (SBDs) are investigated on n-SiC substrate, which have very low onset voltage VF = 0.43 V, high reverse blocking VBR >; 1000 V, very low capacitive charge of 0.213 nC/A, and a very fast recovery time of 10 ps.
Abstract: GaN-based heterostructure lateral Schottky barrier diodes (SBDs) grown on n-SiC substrate are investigated in this letter. These SBDs own very low onset voltage VF = 0.43 V, high reverse blocking VBR >; 1000 V, very low capacitive charge of 0.213 nC/A, and a very fast recovery time of 10 ps. These unique qualities are achieved by combining lateral topology, GaN:C back-barrier epitaxial structure, fully recessed Schottky anode (φB = 0.43 eV), and slanted anode field plate in a robust and innovative process. Diode operation at elevated temperature up to 200 °C was also characterized.
151 citations
TL;DR: In this paper, an enhancement of punchthrough voltage in AlGaN/GaN high-electron-mobility transistors was presented by increasing the electron confinement in the transistor channel using an AlGAN buffer-layer structure.
Abstract: In this paper, we present an enhancement of punchthrough voltage in AlGaN/GaN high-electron-mobility-transistor devices by increasing the electron confinement in the transistor channel using an AlGaN buffer-layer structure. An optimized electron confinement results in a scaling of punchthrough voltage with device geometry and a significantly reduced subthreshold drain leakage current. These beneficial properties are pronounced even further if gate-recess technology is applied for device fabrication. Physical-based device simulations give insight in the respective electronic mechanisms.
143 citations
TL;DR: In this article, a detailed analysis of the stressing mechanisms for highly rugged low-noise GaN monolithic-microwave integrated-circuit amplifiers operated at extremely high input powers is presented.
Abstract: This paper presents a detailed analysis of the stressing mechanisms for highly rugged low-noise GaN monolithic-microwave integrated-circuit amplifiers operated at extremely high input powers. As an example, a low-noise amplifier (LNA) operating in the 3-7-GHz frequency band is used. A noise figure (NF) below 2.3 dB is measured from 3.5 to 7 GHz with NF<1.8 dB between 5-7 GHz. This device survived 33 dBm of available RF input power for 16 h without any change in low-noise performance. The stress mechanisms at high input powers are identified by systematic measurements of an LNA and a single high electron-mobility transistor in the frequency and time domains. It is shown that the gate dc current, which occurs due to self-biasing, is the most critical factor regarding survivability. A series resistance in the gate dc feed can reduce this gate current by feedback, and may be used to improve LNA ruggedness
139 citations
TL;DR: In this paper, the gate degradation was found to be weakly dependent on temperature with an activation energy of 0.1 eV, and the maximum allowed gate operating voltage was estimated using the Weibull statistics.
Abstract: Gate reliability of normally-off p-type-GaN/AlGaN/GaN high-electron mobility transistors grown on Si substrate subjected to forward bias stress at different gate voltages and temperatures was analyzed. Stress-induced gate current degradation was found to be consistent with the percolation process. Obtained time-to-breakdown data were interpreted using the Weibull statistics, and the maximum allowed gate operating voltage was estimated. The gate degradation was found to be weakly dependent on temperature with an activation energy of 0.1 eV.
133 citations
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TL;DR: In this article, a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation is presented.
Abstract: Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation.
1,648 citations
TL;DR: In this paper, a general review of the advances in widebandgap semiconductor photodetectors is presented, including SiC, diamond, III-nitrides and ZnS.
Abstract: Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors.
1,194 citations
TL;DR: Several device technologies for realizing normally off operation that is highly desirable for power switching applications are presented and the examples of circuit applications that can greatly benefit from the superior performance of GaN power devices are demonstrated.
Abstract: In this paper, we present a comprehensive reviewand discussion of the state-of-the-art device technology and application development of GaN-on-Si power electronics. Several device technologies for realizing normally off operation that is highly desirable for power switching applications are presented. In addition, the examples of circuit applications that can greatly benefit from the superior performance of GaN power devices are demonstrated. Comparisonwith other competingpower device technology, such as Si superjunction-MOSFET and SiC MOSFET, is also presented and analyzed. Critical issues for commercialization of GaN-on-Si power devices are discussed with regard to cost, reliability, and ease of use.
922 citations
Nagoya University1, University of Grenoble2, University of Padua3, University of Liverpool4, Hong Kong University of Science and Technology5, Massachusetts Institute of Technology6, HRL Laboratories7, University of Sheffield8, Katholieke Universiteit Leuven9, Fraunhofer Society10, Nagoya Institute of Technology11, University of Notre Dame12, Virginia Tech13, Infineon Technologies14, University of Glasgow15, University of Texas at Austin16, University of Bristol17, National Institute of Advanced Industrial Science and Technology18, University of Cambridge19, Cardiff University20, Zhejiang University21
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
Sandia National Laboratories1, University of California, Davis2, Massachusetts Institute of Technology3, Cornell University4, United States Army Research Laboratory5, Ohio State University6, University of California, Santa Barbara7, Boston University8, North Carolina State University9, Purdue University10, Georgia Institute of Technology11, Michigan State University12, Air Force Research Laboratory13, National Institute of Information and Communications Technology14, University of South Carolina15, United States Naval Research Laboratory16, Arizona State University17, University of Illinois at Urbana–Champaign18, Vanderbilt University19
TL;DR: The UWBG semiconductor materials, such as high Al‐content AlGaN, diamond and Ga2O3, advanced in maturity to the point where realizing some of their tantalizing advantages is a relatively near‐term possibility.
Abstract: J. Y. Tsao,* S. Chowdhury, M. A. Hollis,* D. Jena, N. M. Johnson, K. A. Jones, R. J. Kaplar,* S. Rajan, C. G. Van de Walle, E. Bellotti, C. L. Chua, R. Collazo, M. E. Coltrin, J. A. Cooper, K. R. Evans, S. Graham, T. A. Grotjohn, E. R. Heller, M. Higashiwaki, M. S. Islam, P. W. Juodawlkis, M. A. Khan, A. D. Koehler, J. H. Leach, U. K. Mishra, R. J. Nemanich, R. C. N. Pilawa-Podgurski, J. B. Shealy, Z. Sitar, M. J. Tadjer, A. F. Witulski, M. Wraback, and J. A. Simmons
785 citations