Chapter 2
Zinc Oxide Nanostructures: Advances and Applications
Edited by Magnus Willander
Copyright © 2014 Pan Stanford Publishing Pte. Ltd.
ISBN
978-981-4411-33-2 (Hardcover), 978-981-4411-34-9 (eBook)
www.panstanford.com
Optical Properties of and Optical Devices
from ZnO-Based Nanostructures
The current state of optical properties of ZnO-based nanostructures
is discussed in terms of optical recombination, of bandgap
engineering and of nanoheterostructures such as core–shell quantum
wells and quantum dots. Whispering gallery and Fabry–Perot modes
are reviewed in the section on cavity effects, together with regular
and random lasing in ZnO nanostructures. First results on Raman
and infrared spectroscopy of nanostructures are listed. Promising
optical device applications of ZnO nanowires include electrically
pumped lasing arrays, photodetectors, and second harmonic
generation.
2.1 Introduction
ZnO develops one of the richest families of different nanostructures,
concerning irst the huge variety of different structures and shapes,
Michael Lorenz, Martin Lange, Christian Kranert,
Christof P. Dietrich, and Marius Grundmann
Semiconductor Physics Group, Institut für Experimentelle Physik II,
Universität Leipzig, Linnéstr. 5, D-04103 Leipzig, Germany
mlorenz@physik.uni-leipzig.de
44
Optical Properties of and Optical Devices from ZnO-Based Nanostructures
and second the corresponding piezoelectric, optical, and electrical
properties [1–4]. The excellent luminescence properties of single
selected ZnO nanowires were demonstrated by a full width of half
maximum (FWHM) of the excitonic luminescence around 1 meV
at 9 K, being close to best FWHM values of epitaxial thin ilms and
near standard values of bulk single crystals [5]. First indications for
stimulated emission at room temperature, for the basic concepts
see [6], were provided for optically pumped ZnO nanorods
by Yang, as mentioned in [1]. Quantum coninement effects in
nanometer-thin ZnO nanobelts are obvious by a blue-shift of the
photoluminescence peak [1, 7]. Whispering gallery modes in ZnO
micro- and nanorods were demonstrated for the visible green
emission band by Nobis [8, 9]. Later, whispering gallery mode
lasing in the excitonic UV band was shown by Czekalla [10, 11] and
others. First device applications of ZnO nanowires are reported only
recently, for example photocurrent gas sensors and light-emitting
diodes (LEDs) [2, 12]. Another promising application could be the
near-surface light wave manipulation by engineered ZnO nanowire
arrays [13]. Hierarchical structures made of networks of nanotubes
and nanowires [14] or ZnO nanoplate-nanowire architectures [15]
may open new directions for integrated device applications.
This chapter on optical properties of and optical devices from
ZnO nanostructures is organized as follows: First, the optical
recombination, bandgap engineering, and nanoheterostructures
are discussed, and then cavity effects, including whispering gallery
and Fabry–Perot modes, and regular and random lasing are
reviewed. The state of Raman and infrared spectroscopy is shown,
and inally the demonstration of irst optical devices based on ZnO
nanowires is reviewed. The latter include electrically pumped light-
emitting diodes and lasers, photodetectors, and second harmonic
generation devices.
2.2 Optical Recombination
The optical properties of ZnO-based nanostructures that can
be grown by various growth techniques are strongly connected
with other properties of the nanostructure itself. In this regard,
luminescence measurements are often carried out, in order to
conclude from the optical properties to other properties, e.g., crystal
quality, defects, and dopants and their concentration. In addition,

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