Transcript ZnO2 (Zinc oxide)

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ZnO (Zinc oxide)
by
Alexander Glavtchev
Why is ZnO interesting?
Widely used:
• medicinal purposes (colds, rashes, antiseptics, sunscreen lotions)
• used in manufacturing of rubber as rubber cure (or as filler)
• pigment for paints and coatings
• in electronics, used mainly in laser diodes, LED’s, transparent thin
film coatings, and various piezoelectrics
Bright future:
• shows promising signs in the field of nanotechnology, UV detecors,
nanoscale detectors and actuators
• direct bandgap semiconductor that could replace silicon as the main
substrate in chip manufacturing (if it can be easily/cheaply p-doped)
• dual semiconductor and piezoelectric properties!!
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Properties
Melting Point: 1975 °C
High electron mobility: >100cm2/Vs
High exciton binding energy: ~60meV (electron-hole binding energy)
Direct bandgap: 3.3eV
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Piezoelectric Properties
The output amplitude is related to
the input signal by:
Lithium niobate (LiNbO3) and
Lithium tantalate (LiTaO3) are
currently two very-widely used
piezoelectric crystals due to their
high piezoelectric strain coefficients.
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Piezoelectric Properties
Can produce voltage output from
applied stress (strain), or produce
stress when voltage is applied.
Nanobelts and various nanoscale
features of ZnO give higher
piezoelectric constants (likely due to
less dislocations and the impurity-free
single-crystalline structures).
Piezoelectrics used in: sensors
(acoustic and electronic, as pickups in
electric guitars, detection/generation
of sonar waves, etc.); actuators (highprecision motors, loudspeakers,
atomic force microscope probe
control); possible future use in
vibration and noise reduction
(housing, automobiles).
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Semiconductor Properties
• Zinc oxide is a direct wide-bandgap semiconductor (~3.3-3.4eV).
• Allows for efficient photon emission, as in LED’s or laser diodes
(rather than phonon emission with energy loss and heat generation).
• Can easily be n-doped with aluminum, indium, or extra zinc.
• Possesses high electron mobility and photoconductivity – can help
speed up currents in semiconductor devices.
Drawbacks:
• p-doping is currently very difficult and inefficient and has prevented
mass manufacturing of ZnO-based wafers.
• High-purity ZnO grown on substrates other than sapphire has been
challenging.
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Nano-Structures
• Zinc oxide shows great potential for nanoscale electro-mechanical
fabrication.
• Highly-symmetric, singly-crystalline nanoneedles, nanowires,
nanobelts, nanorings, nanohelixes, nanocombs, etc.
• Hexagonal (wurtzite) structure helps lattice-matching and
controlled growth.
• Positive Zn surfaces and negative O surfaces create electric dipoles
that facilitate polarization growth along certain directions and
planes under applied voltage and temperature.
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Nano-Structures
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Summary
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ZnO displays dual semiconductor and piezoelectric properties.
Used in laser diodes and LED’s.
Potential to be used as a wide-bandgap semiconductor.
Widely used in many other fields (medicine, farming, pigments).
Zinc oxide nanostructure growth is heavily researched presently.
The substance likely has the largest variety of nanostructures (and
their associated properties) among all known materials.
• It’s hexagonal lattice can easily match catalysts’ lattice structure
and facilitate controlled growth patterns.
• Structures like nanowires, nanobelts and nanorings are of great
interest in photonics research, optoelectronics, nanotechnology, and
biomedicine.
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Sources
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Nanoarchitectures of semiconducting and piezoelectric zinc oxide. JOURNAL OF APPLIED
PHYSICS 97, 044304 s2005d
Piezoelectric Characterization of Individual Zinc Oxide Nanobelt Probed by Piezoresponse
Force Microscope. Nano Lett., Vol. 4, No. 4, 2004
Nanostructures of zinc oxide. Zhong Lin Wang. Materials Today, June 2004.
Photonic band structure of ZnO photonic crystal slab laser. JOURNAL OF APPLIED
PHYSICS 98, 103102 2005
Deformation-Free Single-Crystal Nanohelixes of Polar Nanowires. Nano Lett., Vol. 4, No. 7,
2004
Zinc oxide hexagram whiskers. APPLIED PHYSICS LETTERS 88, 093101 2006
Zinc Oxide Nanostructures: Growth, Properties and Applications. J. Phys.: Condens. Matter
16 (2004) R829–R858
Nitrogen doped zinc oxide thin film. http://repositories.cdlib.org/lbnl/LBNL-54116, 2003
www.wikipedia.com
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