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ZnO (Zinc oxide)

by

Alexander Glavtchev

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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, LEDs, transparent thinfilm 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 mainsubstrate in chip manufacturing (if it can be easily/cheaply p-doped)

dual semiconductor and piezoelectric properties!!

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PropertiesMelting 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 PropertiesThe output amplitude is related tothe input signal by:

Lithium niobate (LiNbO3) andLithium tantalate (LiTaO3) arecurrently two very-widely used

piezoelectric crystals due to theirhigh piezoelectric strain coefficients.

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Piezoelectric PropertiesCan produce voltage output fromapplied stress (strain), or producestress when voltage is applied.

Nanobelts and various nanoscalefeatures of ZnO give higher

piezoelectric constants (likely due toless dislocations and the impurity-freesingle-crystalline structures).

Piezoelectrics used in: sensors(acoustic and electronic, as pickups inelectric guitars, detection/generation

of sonar waves, etc.); actuators (high-precision motors, loudspeakers,atomic force microscope probecontrol); possible future use invibration and noise reduction(housing, automobiles).

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Nano-Structures

Zinc oxide shows great potential for nanoscale electro-mechanicalfabrication.

Highly-symmetric, singly-crystalline nanoneedles, nanowires,nanobelts, nanorings, nanohelixes, nanocombs, etc.

Hexagonal (wurtzite) structure helps lattice-matching andcontrolled growth.

Positive Zn surfaces and negative O surfaces create electric dipolesthat facilitate polarization growth along certain directions andplanes under applied voltage and temperature.

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Nano-Structures

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