There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Principles of Neural Science

This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.

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Phonons and related crystal properties from density-functional perturbation theory

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.

Band parameters for III–V compound semiconductors and their alloys

The need to develop inexpensive renewable energy sources stimulates scientific research for efficient, low-cost photovoltaic devices.1 The organic, polymer-based photovoltaic elements have introduced at least the potential of obtaining cheap and easy methods to produce energy from light.2 The possibility of chemically manipulating the material properties of polymers (plastics) combined with a variety of easy and cheap processing techniques has made polymer-based materials present in almost every aspect of modern society.3 Organic semiconductors have several advantages: (a) lowcost synthesis, and (b) easy manufacture of thin film devices by vacuum evaporation/sublimation or solution cast or printing technologies. Furthermore, organic semiconductor thin films may show high absorption coefficients4 exceeding 105 cm-1, which makes them good chromophores for optoelectronic applications. The electronic band gap of organic semiconductors can be engineered by chemical synthesis for simple color changing of light emitting diodes (LEDs).5 Charge carrier mobilities as high as 10 cm2/V‚s6 made them competitive with amorphous silicon.7 This review is organized as follows. In the first part, we will give a general introduction to the materials, production techniques, working principles, critical parameters, and stability of the organic solar cells. In the second part, we will focus on conjugated polymer/fullerene bulk heterojunction solar cells, mainly on polyphenylenevinylene (PPV) derivatives/(1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61) (PCBM) fullerene derivatives and poly(3-hexylthiophene) (P3HT)/PCBM systems. In the third part, we will discuss the alternative approaches such as polymer/polymer solar cells and organic/inorganic hybrid solar cells. In the fourth part, we will suggest possible routes for further improvements and finish with some conclusions. The different papers mentioned in the text have been chosen for didactical purposes and cannot reflect the chronology of the research field nor have a claim of completeness. The further interested reader is referred to the vast amount of quality papers published in this field during the past decade.

Conjugated polymer-based organic solar cells

This paper gives a systematic comparison of input-and output-second-harmonic termination in X-frequency-band MMICs (8–12 GHz) based on advanced single- and double-heterojunction AlGaN/GaN/(Al)GaN high electron mobility transistors (HEMTs) on SiC substrates. High-efficiency design-strategies are key to make use of the outstanding power capability in group-III-nitride MMICs. The study deals with the bandwidth trade-offs associated with reaching very high PAE-values beyond 55% at 10GHz in cw-operation to a 50 Ohm-load.

Harmonic termination of AlGaN/GaN/(Al)GaN-single-and double-heterojunction HEMTs

This paper introduces two realizations of a Riemann-Pump based digital transmitter geared towards software defined radio in 5G systems. In contrast to traditional digital-to-analog converter (DAC) concepts, the Riemann Pump exhibits a higher signal-to-noise ratio (SNR). Since the used 0.25 μm gallium nitride (GaN) technology has a transit frequency of 30 GHz, an oversampling ratio (OSR) of five for the targeted frequency range from DC to 6 GHz is enabled. As the Riemann Pump serves as a digital driver, a co-integration with a suitable wideband power amplifier is possible to reach high power levels. A hybrid assembly is compared to the fully integrated Riemann Pump circuit in GaN technology. The world’s first measurement data of a two bit resolution Riemann Pump in GaN technology are discussed. Radio frequency (RF) power in the watt level range is measured for frequencies between 0.5 GHz - 12 GHz into a capacitive load representing the input capacitance of a power amplifier.

Riemann-Pump based RF-Power DACs in GaN Technology for 5G Base Stations

We report on a new type of broadband radial stub. It consists of two inclined half-stubs, which are separated by a small gap at their vertices. This radial stub can provide −15 dB rejection over almost 29% fractional bandwidth, which is an 86% improvement over the conventional radial stub. Using this stub in a double-sided (butterfly) configuration results in a −15 dB rejection bandwidth of about 61%, higher by a factor of two than in the case of a conventional butterfly stub. This stub was utilized in the DC-bias paths of a GaN power amplifier, which can provide more than 10 dB of gain between 60 and 110 GHz, resulting in the first-ever GaN power amplifier able to cover the whole W-band (75–110 GHz).

A Novel Type of Broadband Radial Stub

In this work, bar-and disk-shaped resonators were fabricated using $\text{Al}_{0.84}\text{Sc}_{0.16}\text{N}$ thin film. Sensitivity analysis of the resonators' resonance frequencies with respect to the piezoelectric material parameters revealed that resonance analysis can be used for material parameter extraction. An optimization algorithm is employed to determine the piezoelectric material parameters $\text{s}_{11}^{E}, \ \text{s}_{12}^{E}$ , and $\text{d}_{31}$ of $\text{Al}_{0.84}\text{Sc}_{0.16}\text{N}$ from the length-and radial-extensional mode. Using the piezoelectric constitutive equations and combining the results obtained in this work with the results obtained in a previous work, the stress-charge form of elastic and piezoelectric parameters could be derived.

Determination of Elastic and Piezoelectric Properties of Al 0.84 Sc 0.16 N Thin Films

The work shows that the efficiency of symmetrical monolithic normally-off GaN half-bridges on semi-floating Si-substrate depends on load current polarity, unlike discrete half-bridges. Discrete and monolithic half-bridges with intrinsic reverse diodes were characterized up to 350V in buck and floating-buck (or boost) converters, varying load current polarity but maintaining voltage and power. Asymmetric effects from negative substrate-to-source back-gate voltage during high-side conduction are observed, which reduce the channel current depending on its polarity: In buck converters, 1st quadrant high-side conduction is degraded by significantly reduced channel current below the gate. In a floating-buck converter, 3rd quadrant high-side conduction current bypasses the degraded gate region through an intrinsic reverse diode, flowing only through the drain access region, which showed lower degradation from negative back-gating. A duty-cycle independent substrate termination network is proposed to shift the average value of the floating substrate voltage towards positive values, avoiding static back-gating of the high-side transistor. It is shown how vertical buffer leakage at positive substrate voltages, which is not relevant for discrete transistors, limits the monolithic half-bridge's operation voltage. Operation of the monolithic normally-off GaN-on-Si half-bridge with semi-floating substrate in a floating-buck (instead of a buck) converter showed efficiencies above 98% at 200W and 200V.

Oliver Ambacher

Papers

Harmonic termination of AlGaN/GaN/(Al)GaN-single-and double-heterojunction HEMTs

Riemann-Pump based RF-Power DACs in GaN Technology for 5G Base Stations

A Novel Type of Broadband Radial Stub

Determination of Elastic and Piezoelectric Properties of Al 0.84 Sc 0.16 N Thin Films

Asymmetrical Substrate-Biasing Effects at up to 350V Operation of Symmetrical Monolithic Normally-Off GaN-on-Si Half-Bridges