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.

InP DHBT circuits: From device physics to 40 Gb/s and 100 Gb/s transmission system experiments

Abstract: The capacity of fiber-optic telecommunication systems can be increased by higher data rate signaling. We present key analog and digital circuits which find application as building blocks in future very high data rate systems. The circuits are fabricated in our indium phosphide (InP) double-heterojunction bipolar transistor (DHBT) technology. The physical properties of the InP material system, notably high breakdown and high electron mobility, enable functions that are not accessible with current silicon-based high-speed technologies, including SiGe. Device and circuit results are presented, and we report on transmission system experiments conducted with these InP DHBT circuits.

A 95 GHz bandwidth 12 dBm output power distributed amplifier in InP-DHBT technology for optoelectronic applications

Abstract: This paper presents a DC-95 GHz distributed amplifier (DA) based on an InP/GaAsSb/InP 800 nm DHBT technology. The circuit employs five cascode unit cells with 0.8 µm × 6 µm HBTs. To obtain flat small-signal gain and group delay characteristics, inductive peaking is used at the collector of the common-base transistor. The amplifier exhibits 12 dB gain from 1–100 GHz, with S 11 and S 22 below −10 dB throughout the frequency range. DC consumption is only 126 mW and group delay remains below 20 ps up to 65 GHz. The simulated saturated output power reaches 12 dBm with a variation of ±0.75 dB across the entire band of operation. This performance is very useful in high-speed, ultra-low power optical systems.

Broadband THz Detection Using InP Triple-Barrier Resonant Tunneling Diode With Integrated Antenna

Abstract: A broadband THz detector consisting of a triple-barrier InP Resonant Tunneling Diode (RTD) with a monolithically integrated circularly polarized spiral antenna is designed, fabricated, and measured at room temperature. A free space measurement setup is utilized for far-field characterization. The detector (evaluated at zero-bias) is illuminated by a chopped continuous wave signal in the 220–330 GHz band, and the direct detection scheme consists of a lock-in amplifier in voltage mode readout. The measured average responsivity R V is in the range of 750 V/W with a peak of 900 V/W at 257.5 GHz, with the lowest calculated NEP of 2.5 pW/√Hz.

Spatially controlled VLS epitaxy of gallium arsenide nanowires on gallium nitride layers

Abstract: We present Au catalyzed p-GaAs nanowire growth on n-GaN layers as a possible method to grow an arsenide on a nitride compound semiconductor by metal organic vapor phase epitaxy. The GaAs growth position, the nanowire density and the nanowire growth direction are controlled by a combination of vapor–liquid–solid growth and selective area epitaxy. Thus, a spatially controlled nanowire growth is attained, which is mandatory for device fabrication. The growth position is defined by lithographically positioned Au discs on n-GaN. By adapting the growth conditions (QTBAs, presaturation) the nanowire density is optimized. Lateral and vertical anisotropic nanowire growth is attained through VLS growth in structured SiOx openings. Critical technological parameters for successful control of the growth direction are the positioning of the Au catalyst in relation to the SiOx mask, the size of the eutectic in relation to the opening dimensions, and the SiOx thickness. These results lead to distinct pn-junction positions and adjustable nanowire growth dimensions and directions.

Large-Signal Modelling of sub-THz InP Triple-Barrier Resonant Tunneling Diodes

Abstract: A large-signal equivalent circuit model is developed for ultra-high frequency signal generation and detection provided by an InP triple barrier resonant tunneling diode. On-wafer DC and S-parameter measurements on 0.5 um2 and 1 um2 area devices were made from 20 MHz to 67 GHz. The bias dependent measurement data are utilized to extract the parameters of a compact RF model which accurately describes the static and dynamic behavior of the triple barrier resonant tunneling under zero bias and forward bias condition.

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.