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

High sensitive ozone sensors working at room temperature were demonstrated based on In2O3 nanoparticles, which were deposited by metal organic chemical vapor deposition (MOCVD). The resistance of the In2O3 particle containing layer can be tuned over five orders of magnitude after ultraviolet light illumination and oxidation by ozone containing gases. To investigate the light induced effect on In2O3 layer, In2O3 nanoparticles were deposited at different substrate temperatures by MOCVD and the electrical and optical properties of the layers were analyzed. It was found that the layers deposited above 220degC showed a typical linear IN behavior while the layers grown below 220degC revealed a classical Schottky behavior. Furthermore, the In2O3 layers deposited below the critical temperature demonstrated not only an increasing absorption at 3.7 eV, which is the optical band gap of In2O3 thin films, but also two additional absorption peaks located at ~43 and ~5.3 eV, respectively. These differences in structural, electrical and optical properties of In2O3 layers lead to different ozone sensing properties.

Electrical and optical properties of In 2 O 3 nanoparticles prepared by MOCVD

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 of 600 V. The transistor shows excellent DC characteristics up to 53 A in pulsed mode. The realized amplifier shows good performance in continuous wave (CW) mode with an output power of 139 W and an efficiency of 71 % at a frequency of 13.56 MHz, respectively. In pulsed mode, the amplifier exhibits an output power of 431 W for a duty cycle of 10 % which emphasizes the potential of the AlGaN/GaN material system for ISM applications. The comparison of the obtained values with silicon-based semiconductor devices furthermore shows the impressive advantages of AlGaN/GaN-based devices for parameters like current density and power density that are for AlGaN/GaN-based devices by an order of magnitude higher.

AlGaN/GaN power amplifiers for ISM frequency applications

http://www.ifkp.tu-berlin.de/fileadmin/i1/hoffmann/publikationen/paper/Ho_154.pdf

The influence of the Al-content on the optical gain in AlGaN heterostructures

This paper gives a first presentation of an AlGaN/GaN high electron-mobility varactor grown on a high resistivity silicon substrate. The technology is compared to a GaN on silicon carbide technology and the devices are characterized by fitting a large-signal model. Compared to GaN on SiC varactors a similar performance is achieved. Only slightly increased losses due to higher sheet and contact resistance lower the Q-factor of the GaN on Si varactor.

AlGaN/GaN High Electron-mobility Varactors on Silicon Substrate

With the increasing requirements for microelectromechanical systems (MEMS) regarding stability, miniaturization and integration, novel materials such as wide band gap semiconductors are receiving more attention. The outstanding properties of group III-nitrides offer many more possibilities for the implementation of new functionalities and a variety of technologies are available to realize group III-nitride based MEMS. In this work we demonstrate the application of these techniques for the fabrication of full-nitride MEMS. It includes a novel actuation and sensing principle based on the piezoelectric effect and employing a two-dimensional electron gas confined in AlGaN/GaN heterostructures as integrated back electrode. Furthermore, the actuation of flexural and longitudinal vibration modes in resonator bridges are demonstrated as well as their sensing properties.

Oliver Ambacher

Papers

Electrical and optical properties of In 2 O 3 nanoparticles prepared by MOCVD

AlGaN/GaN power amplifiers for ISM frequency applications

The influence of the Al-content on the optical gain in AlGaN heterostructures

AlGaN/GaN High Electron-mobility Varactors on Silicon Substrate

AlGaN/GaN Based Heterostructures for MEMS and NEMS Applications