Nils Weimann

Bio: Nils Weimann is an academic researcher from University of Duisburg-Essen. The author has contributed to research in topics: Heterojunction bipolar transistor & Bipolar junction transistor. The author has an hindex of 27, co-authored 160 publications receiving 7215 citations. Previous affiliations of Nils Weimann include Alcatel-Lucent & Agere Systems.

Optical receiver for amplitude-modulated signals

Abstract: An optical receiver that uses a coherent optical quadrature-detection scheme to demodulate an amplitude-modulated optical input signal in a manner that enables the use of a free-running optical local-oscillator source The optical receiver employs a signal combiner that combines, into an electrical output signal, the in-phase and quadrature-phase electrical signals generated as a result of the quadrature detection of the optical input signal Depending on the frequency offset between the local- oscillator signal and the input signal, the electrical output signal produced by the signal combiner can be a desired baseband signal or an intermediate-frequency signal The latter signal can be demodulated to recover the baseband signal in a relatively straightforward manner, eg, using a conventional intermediate-frequency electrical demodulator coupled to the signal combiner

A 330 GHz active frequency quadrupler in InP DHBT transferred-substrate technology

Abstract: This paper presents a wideband 330 GHz frequency quadrupler using 0.8 µm transferred substrate (TS) InP-HBT technology. The process includes a heat-spreading diamond layer, which improves the power handling capability of the circuit. The quadrupler delivers −7 dBm output power at 325 GHz, at a DC consumption of only 40 mW, which corresponds to 0.5 % of efficiency. It achieves 90 GHz bandwidth and exhibits very low unwanted harmonics. The circuit utilizes a balanced architecture. The results demonstrate the potential of the InP TS.

High power GaN/AlGaN/GaN HEMTs operating at 2 to 25 GHz grown by plasma‐assisted MBE

Abstract: We report on the growth and power performance of GaN/AlGaN/GaN high electron mobility transistors (HEMTs) grown by plasma-assisted molecular beam epitaxy (MBE) on semi-insulating SiC substrates. We detail the MBE growth conditions that consistently produce high mobility two-dimensional electron gases (2DEGs) with room temperature mobility of similar to1400 cm(2)/Vs at a sheet density of 1.2 x 10(13) cm(-2). Transistors fabricated from these layers have demonstrated power densities in excess of 8 W/mm at 2 GHz, 6 W/mm at 7 GHz, and 3 W/mm at 25 GHz. All power data is achieved without the use of a SiN surface passivation layer. Central to the achievement of high power operation is the reduction of RF dispersion. Our growth studies have focused on the suppression of RF dispersion and maximizing RF output power. Pulsed I-V and gate lag measurements are used to quantify the amount of dispersion in different heterostructure designs. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

InP double-hetero bipolar transistor technology for 130 GHz clock speed

Abstract: Indium Phosphide-based Hetero Bipolar Transistors (HBTs) have shown strong potential for mm-wave power electronics and mixed-mode applications beyond 100 GHz clock speed. We have developed a planar fabrication technology using all dry etched mesas, which scales to 0.25 µm emitter size. Devices show cut-off frequencies of ft = 380 GHz and fmax = 380 GHz simultaneously (optimized for highest fmax) or ft = 410 GHz and fmax = 340 GHz (optimized for ft). As technology test vehicles, we have realized static-by-four divider circuits running at up to 130 GHz with a baseline epitaxial structure yielding ft = 330 GHz and fmax = 300 GHz; Voltage-Controlled oscillators fabricated in the 380 GHz technology delivered power output of 0 dBm at 180 GHz. The possibility of reducing the extrinsic base-collector capacitance along with the device height by selective ion-implantation of the subcollector is explored. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Band parameters for III–V compound semiconductors and their alloys

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.

Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures

Abstract: Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face AlxGa1−xN/GaN/AlxGa1−xN and N-face GaN/AlxGa1−xN/GaN heterostructures used for the fabrication of field effect transistors. Analysis of the measured electron distributions in heterostructures with AlGaN barrier layers of different Al concentrations (0.15

AlGaN/GaN HEMTs-an overview of device operation and applications

Abstract: Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor seems the most promising. This paper attempts to present the status of the technology and the market with a view of highlighting both the progress and the remaining problems.

Alternative Plasmonic Materials: Beyond Gold and Silver

Abstract: Materials research plays a vital role in transforming breakthrough scientific ideas into next-generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions.

Gan : processing, defects, and devices

Abstract: The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.