Department of Physics and Astronomy
University of Canterbury
PHYS480 RESEARCH PROJECTS
Growth and Characterisation of Thin Films
Assoc. Prof. Roger Reeves
Our group has a programme that researches the growth and characterisation of thin films. The
applications of these films are with modern optoelectronic materials. For example ZnO is a
wide-band gap semiconductor that will be used in advanced lighting applications and high
density information storage.
We grow films using Pulsed Laser Deposition which is a thin film growth technique that uses
a high-powered laser to vapourise a material that can then condense onto a substrate to form the
film. This technique uses a solid target and thus has considerable advantages where the
substance to be grown has a high melting point. The growth takes place in a vacuum chamber
where the atmosphere can be controlled by introduced gases. For example we have had used the
pressure of an oxygen atmosphere in ZnO growth to control the film properties.
The main characterisation of these films is optical spectroscopy where we use laser excitation
to induce the films to emit light. The wavelengths of the emitted photons tell us about the states
in the film while the efficiency of the emission informs us about the quality of the film. Other
experiments are photoconductivity, surface morphology and electrical conductivity (the Hall
effect). We have a very close collaboration with the Electrical and Computer Engineering
Department in this programme.
Project 1: Investigation of persistent luminescence in single crystal zinc oxide.
ZnO is a wide bandgap semiconductor with many interesting optical and electrical properties
that make it suitable for such applications as Solar Cells, piezo electric devices, UV lasers, and
high temperature electronics. It is a brilliant emitter and it is no wonder that numerous
photoluminescence investigations exist of the near band gap recombinations. In high quality
bulk crystals the luminescence line width of excitonic recombination is as narrow as 40 µeV and
many fine spectroscopic details have been observed.
ZnO is radiation hard, thus electronic devices may operate in satellites circling in low earth
orbit. With a band gap of 3.36 eV ZnO is a solar blind material and many applications such as
transparent front electrodes in solar cells make use of this fact.
Recent experiments show strong indications of optical emissions from the crystal long after
the excitation source has been removed, persisting for up to one minute. This phenomenon has
been largely unreported in the literature and represents sample opportunity for exciting and
original, not to mention publishable, research. This project will require you to investigate, model
and report your findings on spectral shape of the luminescence and its temporal evolution.
The experiments in this project will be:
Photoluminescence
Project 2: Growth of thin film photorefractive films
Photorefractive materials are crystals that change their refractive index when subject to high
light intensities. Additionally they change their refractive index when electric fields are applied
and thus these crystals are found as the fast switches for optical pulses in modern fibre-optic
Assoc. Prof. Roger J. Reeves
PHYS480 Projects 2007
roger.reeves@canterbury.ac.nz
Department of Physics and Astronomy
University of Canterbury
based communication. The changing refractive index with light has application in optical
switching and beam amplification.
In this project we will be using the PLD facility to grow thin film photorefractive crystals.
Such films could be used as the template for hybrid devices where a photorefractive organic
materials is sandwiched between crystal photorefractive material. Such devices may have orders
of magnitude higher optical amplification properties and thus be cheaper and more efficient than
all-crystal devices.
The experiments in this project will be:
PLD growth, optical absorption/reflection, surface morphology (AFM etc)
Project 3: Growth and optical characterisation of MnF2 thin film films
MnF2 is a classical antiferromagnetic crystal with a Neel temperature of 67K, ie the magnetic
spins on the Mn2+ ions line up in an alternate pattern below this temperature. Through our
collaboration with the Ioffe Institute in Russia we have investigated MnF2 films grown by
molecular beam epitaxy and found that it can have a new type of crystal phase when very thin.
In this project we will grow MnF2 films by PLD to see if they have different properties to those
grown by MBE. PLD can be a lower temperature growth technique and thus we may be able to
get nanostructures of MnF2. Because of quantum confinement effects these structures may have
different antiferromagnetic phase temperatures.
The experiments in this project will be:
PLD growth, optical absorption/reflection, photoluminescence, surface morphology (AFM
etc)
Assoc. Prof. Roger J. Reeves
PHYS480 Projects 2007
roger.reeves@canterbury.ac.nz