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.

SciFab -a wafer-level heterointegrated InP DHBT/SiGe BiCMOS foundry process for mm-wave applications

Abstract: We present a wafer-level heterointegrated indium phosphide double heterobipolar transistor on silicon germanium bipolar-complementary metal oxide semiconductor (InP DHBT on SiGe BiCMOS) process which relies on adhesive wafer bonding. Subcircuits are co-designed in both technologies, SiGe BiCMOS and InP DHBT, with more than 300 GHz bandwidth microstrip interconnects. The 250 nm SiGe HBTs offer cutoff frequencies around 200 GHz, the 800 nm InP DHBTs exceed 350 GHz. Heterointegrated signal sources are demonstrated including a 328 GHz quadrupling source with dBm RF output power. A common design kit for full InP DHBT/SiGe BiCMOS co-design was set up. The technology is being opened to third-party customers through IHP's multi-purpose wafer foundry interface. Microphotograph of InP DHBT / SiGe BiCMOS wafer

High-reflectivity ultraviolet AlGaN∕AlGaN distributed Bragg reflectors

Abstract: We demonstrate high-reflectivity crack-free Al0.18Ga0.82N∕Al0.8Ga0.2N distributed Bragg reflectors (DBR) for the spectral region around 350nm grown by molecular-beam epitaxy on thick GaN templates. The structural quality of the DBR layers is maintained by compensating the compressive and tensile stress in each λ∕4 pair. This approach results in the lowest elastic strain energy and allows the growth of thick coherently strained DBRs. A 25 period mirror provides a 26nm wide stop band centered at 347nm with the maximum reflectivity higher than 99%.

Monolithic InP Dual-Polarization and Dual-Quadrature Coherent Receiver

Abstract: We realized a monolithic dual-polarization dual-quadrature coherent receiver with balanced detection on InP using a single epitaxial step. It monolithically integrates the polarization splitters, 90° hybrids, and balanced photodiodes in 4.1 mm2 . We demonstrate reception of 112-Gb/s polarization-division-multiplexed quadrature phase-shift keying with 17.3-dB optical signal-to-noise ratio at 10-3 bit-error rate.

Smooth and vertical-sidewall InP etching using Cl2/N2 inductively coupled plasma

Abstract: Inductively coupled plasma (ICP) operated in the reactive-ion etching mode is used for mesa etching of InP using Cl2/N2 chemistry with a Ni metal mask. Etch rates of approximately 140 nm/min with very smooth and vertical sidewalls are obtained at a dc bias of 120 V. The effects of temperature, gas flow, chamber pressure, ICP source power, and substrate bias power on etch rate are studied; sidewall profile and surface morphology will be discussed.

High gain-bandwidth differential distributed InP D-HBT driver amplifiers with large (11.3 V/sub pp/) output swing at 40 Gb/s

Abstract: High-performance and compact 40-Gb/s driver amplifiers were realized in 1.2-/spl mu/m emitter double-heterojunction InGaAs-InP HBT (D-HBT) technology with a maximum cut-off frequency (f/sub T/) of 150 GHz and a maximum oscillation frequency (f/sub max/) of 200 GHz. Two-stage differential drivers feature a lumped input and fully distributed output stage and deliver a maximum differential output swing of 11.3 V peak-to-peak (V/sub pp/) at 40 Gb/s with less then 350 fs of added rms jitter and rise and fall times of about 7 ps while consuming a total power of 3 W. When biased at a lower output swing of 6.3 V/sub pp/, excellent 40-Gb/s eyes with a 7-ps fall time, 6-ps rise time, and no observable jitter deterioration compared with the input source are obtained at a reduced power consumption of 1.7 W. On-wafer measured differential S-parameters show a differential gain of 25 dB, 50 GHz bandwidth, and input and output reflection below -20 dB from 2 to 45 GHz. The amplifiers' small die size (1.0/spl times/1.7 mm), relatively low power consumption, large output swing, and ability to have dc coupled inputs and outputs enable compact 40-Gb/s optical transmitters with good eye opening for both conventional transmission formats such as nonreturn-to-zero and return-to-zero and alternative formats such as duobinary and differential phase shift keying.

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.