Plasma Technology  

 

Zinc Oxide (ZnO) is a direct band-gap (E.g.=3.37eV)
semiconductor with a large excitation binding energy
(60meV), exhibiting near UV emission, transparent
conductivity and piezoelectricity. Moreover, ZnO is
biocompatible and can be used for biomedical
applications without coating.

Electronics - ZnO nanowires and nanorods are good
candidates for nanometre scale electronic applications,
such as sensors or field emission transistors, because
of their high sensitivity to the chemical environment.
The sensing process is related to oxygen vacancies on
the surface that influence the electronic properties
of ZnO.

Optoelectronics - ZnO nanowires and nanorods are also
potentially good candidates for nanometre scale
photonic device applications, ultraviolet photo-
detectors and light emitting devices. Both p-type ZnO
nanowires and n-type ZnO nanowires can be produced
as positively and negatively charged semiconducting
materials, this forms good foundation to make light
emitting diodes (LED), in which, as an electron meets
a hole, it falls into a lower energy level and releases
energy in the form of a photon of light.

Photo Voltaic - ZnO nanowires and nanorods can be
used for fabrication of solar cells that can be dye-
sensitised using liquid or solid (hole conductor)
electrolyte, because ZnO has a wide bandgap,
high charge carrier mobility and can give a high
surface area for efficient dye-sensitization
and light harvesting.

Chemistry - ZnO nanowires and nanorods can promote
catalyst reactions with light as energy source, i.e. they
can be used as photocatalysts.

Biomedical - The biocompatibility of ZnO nanowires
and nanorods along with their electro-optical properties
makes them suitable for active biomedical devices.



Vertically aligned ZnO nanorods
on GaN-coated sapphire
The nanorods have an average length of 400 nm.
The structures are catalysed by Au nanoparticles.
Courtesy of University of Cambridge
Department of Engineering



Stoichiometry of ZnO Nanorods
Normalised quantitative analysis
of the X-ray emission peaks from
Energy-dispersive X-ray spectrum
indicates almost perfect stoichiometry
of the nanorods.

The nanorods were detached
from the growth substrate and
dispersed onto a copper grid coated
with a lacey carbon film.


ZnO Nanowire Growth

 

Zinc precursor (C2H5)2Zn

Oxidising agent O2

Growth temperature 450 625°C

Growth pressure 300 1000 mTorr

Axial growth rate ~ 7nm/min

Substrates used Si(100), Al2O3 (11-20),
GaN-coated Al2O3

 

Process benefits

Both liquid and gases precursors can be
delivered controllably.

Load-locked system offer shorter cycle times,
as no cooling of the growth chamber is required
to exchange samples.


PECVD and CVD technology

 

Nanofab


 


Photoluminescence spectrum of ZnO nanorods
grown on a Si(100) substrate. The strong
ultraviolet emission at around 381 nm is attributed
to the near-band-edge emission of the wide
bandgap ZnO. No broad defect-related green
peak is observed indicating good crystallinity of
the ZnO material.

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