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.

Effect of dislocations on local transconductance in AlGaN/GaN heterostructures as imaged by scanning gate microscopy

Abstract: The spatial variations of transconductance in AlGaN/GaN heterostructures were mapped using a conducting tip atomic force microscope. The conducting tip locally modulates the two-dimensional electron gas (2DEG) while the change in the drain current was monitored as a function of tip position. A spatial resolution of 250 nm was obtained. This technique enables us to investigate the role of defects in transistor performance. In particular, when biased near the depletion of the 2DEG, the transconductance map displays a cell structure, with low signal regions correlating with the positions of negatively charged threading dislocations.

High-Speed Low-Loss Schottky-i-n InP-Based Optical Modulator for RF Photonics

Abstract: An InP-based high-speed optical modulator is presented. The Schottky-i-n waveguide structure on InP-based material was used to reduce the switching voltage Vpi and the excess loss, while maintaining high-modulation efficiencies. To minimize residual amplitude modulation and to improve power handling capability, the bulk electrooptic effect in InGaAlAs was utilized for phase shifting. As a result, a simple structure InAlAs-InGaAlAs Mach-Zehnder optical modulator with traveling-wave electrodes was fabricated and characterized. This device achieved a switching voltage Vpi of 3.6 V, extinction ratio (>23 dB) and high-speed operation at 1.55-mum wavelength

Triple-Barrier Resonant-Tunnelling Diode THz Detectors with on-chip antenna

Abstract: Signal detection at (sub-)mm-wave frequencies via a single chip size component is discussed. The monolithic integration consists of high current density InP-based Triple Barrier Resonant Tunneling Diode into an on-chip antenna. The asymmetrical current voltage characteristic of the Triple Barrier Resonant Tunneling Diode enables signal detection at zero bias. A very high responsivity above 250 GHz is experimentally demonstrated. Low temperature DC rectification factor of the diode is investigated and a thermionic current contribution over the temperature is presented.

Nonolithic photonic integrated circuit

Abstract: An optical device includes a waveguide slab, first and second input port couplers, and first and second output port couplers located over a planar optical substrate. The waveguide slab has a plane of symmetry. The first and second input port couplers extend from the waveguide slab and have an input coupler pair axis located about midway between the first and second input port couplers. The input coupler pair axis is offset at a nonzero first distance from the plane of symmetry. The first and second output port couplers extend from the waveguide slab and have an output coupler pair axis located about midway between the first and second output port couplers. The output coupler pair axis is offset at a different nonzero second distance from the plane of symmetry.

Method for growing layers of group III-nitride semiconductor having electrically passivated threading defects

Abstract: One method includes epitaxially growing a layer of group III-nitride semiconductor under growth conditions that cause a growth surface to be rough. The method also includes performing an epitaxial growth of a second layer of group III-nitride semiconductor on the first layer under growth conditions that cause the growth surface to become smooth. The two-step growth produces a lower density of threading defects. Another method includes epitaxially growing a layer of group III-nitride semiconductor on a lattice-mismatched crystalline substrate and then, chemically treating a growth surface of the layer to selectively electrically passivate defects that thread the layer.

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.