Photothermal beam deflection for non-destructive evaluation of semiconductor thin films

119 Pages·2011·3.44 MB·English

by  Anita R Warrier

Photothermal beam deflection for
non-destructive evaluation of semiconductor
thin films

Thesis submitted to

Cochin University of Science and Technology

In partial fulfilment of the requirements for the award of the degree of

DDDDooooccccttttoooorrrr ooooffff PPPPhhhhiiiilllloooossssoooopppphhhhyyyy

Under the Faculty of Science

Anita R Warrier

Applied Optics Division
Department of Physics
Cochin University of Science and Technology
Cochin 682 022, Kerala, India

August 2010
Photothermal beam deflection for non-destructive evaluation of
semiconductor thin films

PhD thesis in the field of Material Science

Author

Anita R Warrier
Applied Optics Division
Department of Physics
Cochin University of Science and Technology
Cochin 682 022, Kerala, India

Supervising Guide

Prof K P Vijayakumar
Thin film Photovoltaic & Applied Optics Division
Department of Physics
Cochin University of Science and Technology
Cochin 682 022, Kerala, India
[email protected]

Cochin University of Science and Technology, Cochin 682 022, Kerala, India
August 2008
Dedicated to my beloved grandma,
Who chose the abode of God.
But continues to inspire me,
And whose loving memories are forever
A reason to smile…
Dr K P Vijayakumar
Professor
Department of Physics
Cochin University of Science and Technology
Cochin 682 022, Kerala, India

Certificate

Certified that the work presented in this thesis entitled “Photothermal beam
deflection for non-destructive evaluation of semiconductor thin films” is based on
the authentic record of research done by Ms Anita R Warrier under my guidance
in the Department of Physics, Cochin University of Science and Technology,
Cochin 682 022 and has not been included in any other thesis submitted for the
award of any degree.

Cochin 22 Dr K P Vijayakumar

Date: (Supervising guide)

Phone: [phone] extn 33 Fax: [phone] Email: [email protected]
Declaration

I hereby declare that the work presented in this thesis entitled ”Photothermal
beam deflection for non-destructive evaluation of semiconductor thin films” is
based on the original research work done by me under the supervision and
guidance of Prof K P Vijayakumar, Department of Physics, Cochin University of
Science and Technology, Cochin 682 022 and has not been included in any other
thesis submitted previously for the award of any degree.

Cochin 22
Date: Anita R Warrier
Acknowledgements

It is the human mind’s quest to ponder the mystery of creation, sustenance and
destruction. This quest is in itself a journey covering the dark and beautiful phases of life
and in the finale what remains is a realisation that, every war we fought and every obstacle
we crossed was worth the life we lived.

I express my deepest gratitude to my guide Prof K P Vijayakumar for steering me
through the journey and holding the torch for me to envisage the beautiful path it covers.
His ideas and visions always helped me understand the problem better and find the
solution. I am indebted to Prof C Sudha Kartha for the moral support I got. I have always
admired her ability to view any predicament in true light and give right focus to work. Her
suggestions and criticism helped me improve in many ways.

I am forever grateful to the Head of the Department, Prof M R Anantharaman and
all my teachers in Physics Department for the interesting and delightful classes during my
post graduation days and the help I received throughout my research period. I am also
grateful to all the staff in this department for assisting me earnestly whenever I approached
them.

I am very much grateful to Dr R Jayakrishnan for the support I received during the
initial stage of my work. His insights and the long discussions we had, helped me view the
problem in a new perceptive. I always cherish the wonderful relation with Pramitha, who is
always a source of strength and happiness and I will forever rejoice the memories of my
days shared with her in this department. I would also like to mention my gratitude to
Vimal for being the patient and trusty friend who listens and lighten the hurdles in the
path.

I would like to thank my seniors Dr Teny Theresa John, Dr M Paul Raj, Dr S
Ramkumar, Dr Ratheesh Kumar P M, K C Wilson, Dr Beena Mary John, Dr R Sreekumar,
Dr V C Kishore, Dr Deepa K G, Dr Tina Sebastian, Dr Meril Mathew for their love and
support. I would always remember with love and affection my juniors Sajeesh, Angel,
Rajesh Menon, Rajesh C S, Sreeroop, Subramanian, Nimmi, Sona, Poornima, Rajeshmon,
Aneesh, Minu, Anaswalih, Santhosh and Deepu for the fun filled days in this department.

I am glad expressing my gratitude to MSc project students Anuradha,
Chandhrasekhar, Anand, Leshma, Abdul Rasheed and Linda. The discussions we had were
thought provoking and improved my understanding of the subject.

And the entire work was possible only because of my mother and father, who in every
turn of life holded my hands gave me strength and supported me whole heartedly to move
forward. I would like to thank my brother and sister for the constant encouragement and
inspirations. The love and support I received from my in laws for this pursuit were
magnificent. I am very much grateful to my husband for the freedom I had in pursuing my
work, despite numerous problems we faced he never let me stray away from the path.
Finally I would like to express my admiration to my son Aditya, who is the beautiful
butterfly that flutters around my life teaching me every day, in every way the true essence
of life and keeps the child in my alive.

I remember with gratefulness all my friends and well wishers for their blessings
and prayer.

Anita R Warrier
X
The scientist does not study nature because it is useful;
He studies it because he delights in it,
And he delights in it because it is beautiful

If nature were not beautiful, it would not be worth knowing,
And if nature were not worth knowing,
Life would not be worth living

Henri Poincare
(French Mathematician 1854-1912)
Preface

Preface
Non-destructive testing (NDT) is the use of non-invasive techniques to determine the
integrity of a material, component, or structure. Engineers and scientists use NDT in a
variety of applications, including medical imaging, materials analysis, and process control.
Photothermal beam deflection technique is one of the most promising NDT technologies.
Tremendous R&D effort has been made for improving the efficiency and simplicity of this
technique. It is a popular technique because it can probe surfaces irrespective of the size of
the sample and its surroundings. This technique has been used to characterize several
semiconductor materials, because of its non-destructive and non-contact evaluation
strategy. Its application further extends to analysis of wide variety of materials. Chapter one
of the thesis covers the principle, application and review of R&D works concerning
photothermal techniques and application.
Instrumentation of a NDT technique is very crucial for any material analysis. Chapter two
explores the various excitation sources, source modulation techniques, detection and signal
processing schemes currently practised. The features of the experimental arrangement
including the steps for alignment, automation, data acquisition and data analysis are
explained giving due importance to details.
Theoretical studies form the backbone of photothermal techniques. The outcome of a
theoretical work is the foundation of an application. Chapter three brings forth the
importance of theoretical studies carried out in this area and explains the steps of
theoretical model developed for analysis of semiconductor thin films. The reliability of the
theoretical model developed and used is proven from the studies done on crystalline
silicon.
The technique is applied for analysis of transport properties such as thermal diffusivity,
mobility, surface recombination velocity and minority carrier life time of the material and
thermal imaging of solar cell absorber layer materials like CuInS , CuInSe and SnS thin
2 2
films. Chapter four briefs the results of the photothermal analysis of these materials and its
application for optimisation of thin film fabrication process.
Chapter five deals with analysis of In S thin films, which are used as buffer layer material in
2 3
solar cells. The various influences of film composition, chlorine and silver incorporation in
this material is brought out from the measurement of transport properties and analysis of
sub band gap levels.
XIII
Preface

The application of photothermal deflection technique for characterization of solar cells is a
relatively new area that requires considerable attention. Chapter six thus elucidates the
theoretical aspects of application of photothermal techniques for solar cell analysis. The
experimental design and method for determination of solar cell efficiency, optimum load
resistance and series resistance with results from the analysis of CuInS /In S based solar
2 2 3
cell forms the skeleton of this chapter.
The Chapter seven attempts to depict the state of art, achievements and future prospects of
the studies done.

XIV