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Nitride Semiconductors. Handbook on Materials and Devices

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describe the use of residual dipolar
couplings to gain insight into the structure and dynamics of glycolipids as
membrane constituents. The theoretical
aspects and the NMR spectroscopic
measurements are covered concisely.
Cline Monteiro and Catharine Herv
du Penhoat present studies on activated
sugars. The collection of data for sugar
nucleotides is described, including the
use of paramagnetic cations.
Part C deals with the application of
NMR spectroscopy to studying the interactions of carbohydrates with biomolecules. In this context Armin Geyer discusses the analysis of carbohydrate–carbohydrate interactions. Here the affinities
are weak in comparison to those for
carbohydrate–protein interactions, and
consequently they are not easy to measure reliably. For covalently bound Lewis–
X structures it was found possible to
measure the homophylic interaction as a
function of the Ca2+ concentration. The
method holds promise for monitoring
conformational aspects of multivalent
carbohydrate–carbohydrate interactions.
Finally, Jesffls Jimnez-Barbero and
Thomas Peters describe transfer-NOE
(Tr-NOE) experiments to study carbohydrate–protein interactions. Such interactions are very common in nature, and
therefore it is very important to have
effective methods for exploring the
molecular details of these processes. An
introduction to Tr-NOE is followed by
experimental details, which provide the
reader with a good insight into how to
apply the method. This approach can
yield information about the conformation
of the ligand in the bound state.
In summary, this book covers many
theoretical and experimental aspects of
the NMR spectroscopy of glycans, which
are treated at the postgraduate level.
The many literature references at the
end of each chapter are useful for the
reader interested in more background
and more experimental details. It can be
recommended for glycoscientists to get
a good impression of the possibilities of
NMR spectroscopy for solving structural problems.
Hans Vliegenthart
Bijvoet Center, Utrecht University
Utrecht (The Netherlands)
4724
Nitride Semiconductors
Handbook on
Materials and
Devices. Edited by
Pierre Ruterana,
Martin Albrecht and
Jrg Neugebauer.
Wiley-VCH, Weinheim 2003.
664 pp., hardcover
E 169.00.—ISBN
3-52–40387-6
Electrically generated light is nowadays
taken for granted. In everyday life we
meet bright billboards, traffic signs, and
color images in cellular phones. Lightemitting diodes (LEDs) based on
nitrides of Group III elements play a
major role in all these luminescent
displays. Compared to the traditional
elemental (Si, Ge) and III–V semiconductors GaAs and GaP, they combine a
wider direct band gap with a high
melting temperature, which makes
them suitable as efficient components
in short-wavelength optoelectronic
devices such as blue light emitting
diodes. In the year 2002, more than
2000 research articles were devoted to
GaN-based materials, emphasizing crystal growth, epitaxy, nanoparticles, and
the development of new devices such as
laser diodes, photodetectors, and transistors, which shows the high level of
scientific and industrial interest in these
materials.
The new handbook Nitride Semiconductors, edited by P. Ruterana, M.
Albrecht, and J. Neugebauer, recognizes
this upsurge of interest and provides an
excellent comprehensive description of
recent developments in GaN-, AlGaN-,
and GaInN-based materials and devices.
The book is divided into three parts:
1. Crystal Growth, 2. Defect Structure,
and 3. Devices.
Part 1 provides the reader with the
fundamentals and recent research
advances in state-of-the-art crystallization techniques. An impressive introduction to the demanding high-pressure
crystallization techniques (20 kbar at
1600 8C) that are necessary to avoid
decomposition of GaN in high-temperature crystallization is given by S.
Porowski (Unipress, Warsaw). The
2 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
materials produced by that method are
suitable substrates for the epitaxial
growth of InGaN MQW-based lasers,
but are not commercially available, and
thus the whole technological development of GaN-based devices relies on
heteroepitaxy. However, since the lattice parameters and thermal expansion
coefficients of substrates such as sapphire and 6H-SiC are not well matched
to GaN, huge densities of dislocations
are generated. The real breakthrough
has been the dramatic improvement of
laser diode lifetimes through the use of
the epitaxial lateral overgrowth (ELO)
technology developed by Nakamura.
Chapter 2 details the application of
ELO using sapphire as well as 6H-SiC
substrates, and ELO implementation is
discussed for the two most important
growth
techniques,
metal–organic
vapor-phase epitaxy (MOVPE) and hydride vapor-phase epitaxy (HVPE),
with particular attention to the generation of defect structures. The fundamentals of plasma-assisted molecular
beam epitaxy (PAMBE), which is not
commercially used, and HVPE are outlined in Chapters 3 and 4. The advantages of using PAMBE and metal–
organic molecular beam epitaxy
(MOMBE) for the growth of InN films
are clearly demonstrated.
A crucial issue for future understanding and improvement of the surface morphology and structure observed
in different growth modes is the development of theoretical methods. Recent
studies of surface reconstruction based
on density-functional methods, and
experimental studies using LEED and
RHEED, are discussed by J. Neugebauer. They show remarkable new features
of polar GaN surfaces, such as the
presence of tetramers, whereas the preferred building blocks on (001) surfaces
of conventional semiconductors are
dimers.
The second half of the handbook
consists of two almost equal parts
devoted to defects in nitride-based semiconductors (Part 2) and to devices using
them (Part 3). The main defect structures, such as threading, stacking-fault,
and interfacial dislocations, are introduced from a crystallographic point of
view in a topological analysis by circuit
mapping, which allows a neat and concise description of defects by a product
Angew. Chem. Int. Ed. 2003, 42, 4723 – 4725
Angewandte
Chemie
of symmetry operations. The practical
application of the concept introduced by
Frank is convincingly illustrated by
several high-resolution electron microscopy (HREM) micrographs of the
corresponding defects. The identification of typical defect structures such as
dislocations, nanopipes, and grain boundaries, which characteristically depend
on the growth conditions and affect the
optical properties, is a crucial step for
the optimization of growth techniques.
In addition, the handbook includes a
detailed description of experimental
HREM techniques for defect and
strain analysis at the atomic level. Particular attention is given to noise reduction techniques such as averaging in real
space, cross-correlation, filtering in
Fourier space, and Wiener-type filtering.
Local stress fields play an important role
in the formation of nanostructure materials and in determining their mechanical and electronic properties. The stress
can induce band-gap modification and
changes in the optoelectronic properties. Quantitative information about the
Angew. Chem. Int. Ed. 2003, 42, 4723 – 4725
strain fields is obtained by simulation of
diffraction contrast images and by using
peak-finding procedures or the geometric-phase method. GaN-based devices
are nowadays products found in everyday life. Light-emitting diodes and laser
diodes based on Group III nitrides play
a major role in luminescent displays and
optical storage systems. A historical
overview of the development of the
field is given by H. Amano, who also
refers to some of the hottest topics in the
nitride field, such as white LEDs that
could eventually replace fluorescent
light tubes. The combination of a blue
LED with yellow phosphors is simple,
and fabrication is easy.
The wide band gap makes GaN and
its heterostructures also attractive for
high-power/high-temperature
fieldeffect transistors (FETs), because
GaN-based FETs can handle not only
high voltages but also high currents,
giving power levels 10–100 times higher
than with silicon- or gallium arsenidebased devices. Applications include lowcost compact amplifiers for radar, satel-
www.angewandte.org
lite, and wireless communication. The
third emerging field of application
described in the handbook makes use of
the photocurrent associated with direct
band-gap transitions in AlxGa1-xN-based
UV photodetectors. The wide band gap
results in a high UV to visible contrast,
and the increase of the band gap with
increasing Al mole fraction (up to
6.2 eV) allows the fabrication of filterfree UV photodetectors. They are promising devices for biological and chemical
sensors, flame sensors, optical communication, and solar UV measurements.
Overall, the new handbook is an
essential reference work for material
scientists, and is equally valuable for
newcomers as well as experts and professionals who are envisioning novel
semiconductor devices or developing
epitaxial growth techniques.
Stefan Kaskel
Max-Planck-Institut f<r Kohlenforschung
M<lheim/Ruhr (Germany)
DOI: 10.1002/anie.200385026
2 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4725
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