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.

/pdf/phonons-and-related-crystal-properties-from-density-3mdybdn8w1.pdf

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

We report on the trade-off between performance and reliability for AlGaN/GaN transistors. It is shown that changes in epitaxial growth, transistor design and process may lead to an improvement in performance but are, at the same time, accompanied by a degradation of device reliability. As a result we show strategies in order to balance performance and reliability as both are linked. Based on these findings we have realized state-of-the-art power bars for mobile communication systems and X-band MMICs for radar applications. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Trade‐offs between performance and reliability in AlGaN/GaN transistors

In this paper, we report on the development of an RF high power amplifier, based on normally-on AlGaN/GaN Heterostructure Field-Effect Transistors (HFETs) on semi-insulating SiC substrates. The amplifier is derived from a transistor with a total gate periphery of 120 mm that exhibits a breakdown voltage better than 420 V. The transistor yields pulsed drain current levels of up to 53 A and therefore is found suitable for the ISM frequency band (industrial, scientific, medical) power applications at 13.56 MHz. The realized amplifier shows good performance in cw mode with an output power of 139 W and an efficiency of 71%, respectively. In pulsed mode, the amplifier exhibits an output power of 431 W for a duty cycle of 10% at a frequency of 13.56 MHz, which emphasizes the high potential of the III–V-compound semiconductor AlGaN/GaN for ISM applications. The comparison of the obtained values with standard silicon based semiconductor devices used for this frequency range furthermore shows the impressive advantages of AlGaN/GaN based devices for parameters like current density and power density that are at least by a factor of 10 higher. In a next step, the ruggedness of the realized amplifier was investigated. Operating the amplifier up to a VSWR of more than 15:1, no damage was observed. The junction temperature during VSWR mismatch was calculated to be more than 249 °C.

AlGaN/GaN power amplifiers for ISM applications

The lifetime and stability of AlGaN/GaN heterostructure eld e ect transistors at high power levels can be enhanced by introducing eld plates to reduce electric eld peaks in the gate drain region. Simulations of the electric eld distribution along the channel using the 2D ATLAS software from Silvaco indicate that above a characteristic drain source voltage three spatially separated electric eld peaks appear, one located at the drain-side edge of the gate foot, one at the end of the drain-sided gate eld plate, and one at the end of the source shield eld plate. The close correlation between lateral electric eld and the electroluminescence due to hot electron related intra-band transitions can be very helpful when optimizing the electric eld distribution in high power devices. Electroluminescence microscopy images of devices with gate and source shield eld plate reveal the peaks located at the locations of enhanced electric eld. By studying the voltage dependence of the electroluminescence peaks the in uence of the eld plates on the electric eld distribution in source drain direction can be visualized.

http://przyrbwn.icm.edu.pl/APP/PDF/125/a125z4p57.pdf

Electroluminescence Investigation of the Lateral Field Distribution in AlGaN/GaN HEMTs for Power Applications

This paper reports on the realization of a dual-band high power Class-ABJ GaN Doherty power amplifier (PA) for base-station transmitter system (BTS) applications. The designed Doherty PA module consists of two individual single-ended high power-efficient AlGaN/GaN PAs with multi-harmonic Class-ABJ termination operating in both UMTS 2.1–2.2 GHz and LTE 2.6–2.7 GHz communication bands. Measurements have been performed on both the single-ended and Doherty PA prototypes driving both modules with a 5 MHz WCDMA signal having different PAR. The measured single-ended PA block yields around 39.3 dBm average POUT as well as 40% and 37% average DE at the two center frequency bands FC=2.15GHz and FC=2.65 GHz when driving it with a WCDMA signal having 5.6 dB PAR. The Doherty PA prototype was tested by using a WCDMA input signal with higher PAR=7.7 dB. These measurement results demonstrate around 40% average drain efficiency and 44 dBm average POUT in the UMTS band at FC=2.15 GHz and around 36% average DE and 42.9 dBm average POUT in the LTE band at FC=2.65 GHz.

Oliver Ambacher

Papers

Trade‐offs between performance and reliability in AlGaN/GaN transistors

AlGaN/GaN power amplifiers for ISM applications

Electroluminescence Investigation of the Lateral Field Distribution in AlGaN/GaN HEMTs for Power Applications

A dual-band UMTS/LTE highly power-efficient class-ABJ Doherty GaN PA

Vertical Buffer Leakage and Temperature Effects on the Breakdown Performance of GaN/AlGaN HEMTs on Si Substrate