PREPARATION AND CHARACTERIZATION
OF TERNARY ALLOY CHALCOGENIDE
SEMICONDUCTOR THIN FILMS PREPARED
BY FLASH EVAPORATION TECHNIQUE
By
PRADYUMNA KUMAR SWAIN
SUBMITTED
IN FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
Department of Physics
INDIAN INSTITUTE OF TECHNOLOGY, DELHI
FEBRUARY 1995
csi,2sy
I. 1. T. ClIE.0-41.
Cir.-4
,Z1... — ....2
oe
CERTIFICATE
This is to certify that the thesis entitled "Preparation and Characterization of Ternary Alloy
Chalcogenide Semiconductor Thin Films prepared by Flash Evaporation Technique" being
submitted by Mr. Pradyumna Kumar Swain to the Indian Institute of Technology, Delhi for
the award of the degree of Doctor of Philosophy in Physics is a record of bonafide research
work carried out by him. Mr. P.K. Swain has worked under my guidance and supervision
for the submission of this thesis.
The thesis or any part thereof has not been submitted to any other university or institute for
the award of any degree or diploma.
Prof. H.K. Sehgal
Materials and Systems Laboratory
Department of Physics
Indian Institute of Technology
New Delhi-110 016
DEDICATED TO
MY PARENTS
ACKNOWLEDGEMENTS
I wish to express my deep sense of gratitude to Prof. H.K. Sehgal for his
continuous and constructive guidance during the course of work reported in this thesis. His
inspiration and kind encouragement were of great help to complete the present investigation.
I am sincerely grateful to Prof. S.C. Mathur and Prof. D.C. Dube for
providing facilities in their laboratory for electrical measurements.
I am grateful to Dr. A.K. Sharma for his invaluable help and moral support
throughout the research period.
I would like to thank Dr. Preeti Kashyap for her constructive suggestions and
helpful advice during the research period.
I am grateful to Mr. V.D. Arora for his help with TEM analyses and Mr.
H.S. Sharma for his help in absorption spectroscopic measurements.
Sincere thanks are due to Mr. G.S. Pati for his valuable help and suggestions.
I am thankful to my friends Ramkumar, Rabi, Pant, Ahuja, Jarwal, Kamran,
Lalit, Pravin, Adda, Mishraji, Saytavir, Anil, Sudershan, Rajanesh and Pradhan for their
help and moral support at the hours of need.
I do not have words to express my gratitude to my parents and family
members for their moral encouragement through out the period of research.
P.K. Swain
ABSTRACT
Structural, optical and electrical properties of thin films of mercury manganese
sulphide, mercury zinc sulphide, lead manganese sulphide and mercury manganese selenide
systems, flash evaporated on optically polished quartz, glass micro slides and freshly cleaved
single crystal KCl substrates maintained at different temperatures (Ts) are reported in this
thesis.
Results of investigations show that it is possible to grow single phase
HgsMni _sS alloy films over the composition range 0.16x0.84. Structural investigations
indicate the presence of f.c.c. lattices in these films. Variation of lattice parameter with
composition can be expressed as per the relation:
a(x)A = 5.63 + 0.53 x;
for the Ts of 175°C films. Presence of a single well defined absorption edge which shifts its
position with composition confirms the presence of a single phase alloy of the type HgxMn,_„S
in the films. The bandgap is observed to increase with increase in mercury concentration 'x'.
Variation of bandgap with 'x' is not linear, but shows a bowing typical of the pseudo-binary
solid solutions. The observed structural and optical characteristics of the films can be
explained on the basis of atom-by-atom condensation process. Increase in d.c. resistivity with
increase in mercury concentration and substrate temperature is correlated to the increase in
bandgap with increase in mercury concentration and increase in graillsize with substrate
temperature (Ts).
Investigations on the mercury zinc sulphide ternary systems suggest the
possibility of obtaining uniphase Hg„Zn i _„S alloy films over a composition range of 0.16 5_
x < 0.84. Transmission electron microscopic investigations indicates the films to have a
ii
polycrystalline b.c.c. structure. The lattice parameter is observed to follow a linear relation,
a(x) A = 5.37 - x;
for the Ts of 175°C films. Presence of a single absorption edge in all the films confirms the
existence of single phase ternary materials of the type HgsZn i _sS in each of the films. Optical
bandgap (Eg) is observed to vary between 3.0 eV and 0.45 eV as the mercury concentration
`x' is increased from 0.16 to 0.84. The observed structural and optical characteristics of the
films can be explained if we consider the films to grow by the atom-by-atom condensation
process. D.C. resistivity of these films decreases with increase in 'x' but increases with Ts.
Resistive behavior could be understood by considering the grain-boundary conduction
mechanism.
PbsMni _sS films with lead concentration (x) varied in the range 0.16x
0.84, are analyzed for their structural, optical and electrical characteristics. Electron
microscopic investigations indicated all films to have a single phase f.c.c. lattice and grow
as epitaxial with <100> zone axes orientations of the grains suggesting the films to contain
ternary materials of the type PbxMni_xS. Variation of lattice parameter with 'x' obeys
Vegard's law as per the relation:
a(x) A = 5.60 + 0.33 x;
which gives the best fit for Ts of 165°C. Presence of a single absorption edge which shifts
towards longer wavelengths confirms the existence of single phase PbsMni _sS materials in
each of the film. The direct optical bandgap is observed to decrease from 2.26 eV and 0.52
eV as the lead concentration is changed from 0.16 to 0.84. Variation of Eg vs 'x' follows a
parabolic relation given by:
Eg(x) = 2.41 - 1.32 x - 1.1 x2 eV.
Structural and optical properties can be explained on the basis of nucleation and growth of
iii
the films taking place by atom-by-atom condensation process. Room temperature d.c.
resistivity of the films increases with T, and decreases with increase in lead concentration.
Variation of resistivity is explained on the basis of 'Kane Model' and grain boundary
trapping mechanism.
Structural investigations carried out on the mercury manganese selenide system
with mercury concentration (x) varied in the range 0.16x 5_ 0.84 indicate presence of
single phase Hg„Mn i_sSe polycrystalline materials with f.c.c. structure in the films. Lattice
parameter varies linearly with 'x' and can be expressed as per the relation;
a(x)A = 5.82 + 0.27 x;
for the Ts of 130°C films. Presence of a single absorption edge in the optical absorption
investigations confirms the existence of a single phase ternary material of the type
HgsMni_sSe in the films. Direct optical bandgap is observed to decrease linearly from
Eg = 3.08 eV for x = 0.16 to Eg = 0.47 eV for x = 0.84; for T. of 225°C films. Structural
and optical characteristics of the films can be explained on the basis of atom-by-atom
condensation process. Room temperature d.c. resistivity decreases with increase in mercury
concentration but increases with increase in T. Resistive behavior could be explained on the
basis of grain boundary conduction mechanism.
iv
CONTENTS
Page No.
Acknowledgements
Abstract
fi
Chapter-IIntroduction
1.1Historical Background
1.2Thin Film Deposition Techniques
1.2.1 Spray Pyrolysis
1.2.2 Solution Growth
1.2.3 Sputtering
1.2.4 Thermal Evaporation
1.2.5 Molecular Beam Epitaxy
1.2.6 Flash Evaporation
1.3The Binary Materials
1.4The Ternary Systems
1
2
2
3
3
3
4
4
5
6
Chapter-IIExperimental Technique
2.1
Introduction
2.2Deposition of Thin film samples
by flash evaporation technique
2.2.1 Experimental set-up
2.2.1 (a) The vacuum system
2.2.1 (b) The flash evaporation assembly
2.2.1 (c) Evaporation Boat
2.2.1 (d) Substrate Heater
2.2.2 Preparation of the films
2.3Transmission Electron Microscopic Studies
2.3.1 Determination of average grainsize
2.4 Optical Bandgap Determination of the film
2.5Electrical Characterization
Chapter-IIIStructural, Optical and Electncat
Properties of Flash Evaporated
HgxMni _xS films
3.1Introduction
3.2Sample Preparation
3.3Experimental Results
3.3.1 Transmission Electron Microscopic
studies of the as grown films
3.3.1 (a) Ts of 65°C films
10
10
10
11
11
11
12
13
13
15
16
17
19
20
•21
21
21
3.3.1 (b) T, of 130°C films
3.3.1 (c) T, of 175°C and 225°C films
3.3.2 Variation of lattice parameter
of the films
3.3.3 Variation of Average grainsize
in the films
3.3.4 Effect of Electron beam heating
on the as grown films
3.3.5 Optical Transmission and
Reflection Measurements :
Determination of Optical Energy
Bandgap in the as grown films
3.3.6 Variation of Optical Bandgap
with Composition
3.3.7 D.C. Electrical Resistivity
Measurements
Discussion
of the results
3.4
3.4.1 The Atom-by-atom condensation
process
3.4.2 Structural Properties
3.4.3 Optical Properties
3.4.4 Electrical Properties
21
22
23
23
23
24
24
25
25
25
28
28
29
Chapter-IV Structural, Optical and Electrical
Properties of Mercury Zinc Sulphide Thin Films
4.1Introduction
4.2Preparation of Sample
4.3Experimental Results
4.3.1 Transmission Electron Microscopic
studies of the as grown films
4.3.1 (a) Ts of 65°C films
4.3.1 (b) T, of 130°C films
4.3.1 (c) T, of 175°C films
4.3.1 (d) Ts of 225°C films
4.3.2 Variation of lattice parameter
of the films
4.3.3 Variation of Average grainsize
in the films
4.3.4 Effect of Electron beam heating
on the as grown films
4.3.5 Optical Transmission and
Reflection Measurements :
Determination of Optical Energy
Bandgap in the as grown films
4.3.6 Variation of Optical Bandgap
with Composition
4. 3. 7 D.C. Electrical Resistivity
Measurements
31
32
33
33
33
33
34
34
35
36
36
36
37
37
4.4Discussion of the results
4.4.1 Structural Properties
4.4.2 Optical Properties
4.4.3 Electrical Properties
38
38
39
40
Structural, Optical and Electrical
Chapter-V
Properties of Lead Manganese Sulphide
Thin Films
5.1Introduction
5.2Preparation of Samples
5.3Experimental Results
5.3.1 Transmission Electron Microscopic
studies of the as grown films
5.3.1 (a) Ts of 65°C films
5.3.1 (b) T, of 130°C films
5.3.1 (c) T, of 165°C films
5.3.1 (d) T, of 225°C films
5.3.2 Variation of lattice parameter
of the films
5.3.3 Variation of Average grainsize
in the films
5.3.4 Effect of Electron beam heating
on the as grown films
5.3.5 Optical Transmission and
Reflection Measurements :
Determination of Optical Energy
Bandgap in the as grown films
5.3.6 Variation of Optical Bandgap
with Composition
5.3.7 D.C. Electrical Resistivity
Measurements
5.4 Discussion
5.4.1 Structural Properties
5.4.2 Optical Properties
5.4.3 Electrical Properties
41
42
43
43
43
43
44
44
45
45
45
46
46
47
47
47
48
49
Chapter-VI Structural, Optical and Electrical
Properties of Mercury Manganese Selenide
Thin Films
6.1Introduction
6.2Preparation of Sample
6.3Experimental Results
6.3.1 Transmission Electron Microscopic
studies of the as grown films
6.3.1 (a) Ts of 65°C films
6.3.1 (b) Ts of 130°C films
6.3.1 (c) T, of 175°C films
51
52
53
53
53
53
54.
6.3.1 (d) 'I', of 225°C films
6.3.2 Variation of lattice parameter
of the films
6.3.3 Variation of Average grainsize
in the films
6.3.4 Effect of Electron beam
heating
on the as grown films
6.3.5 Optical Transmission and
Reflection Measurements :
Determination of Optical Energy
Bandgap in the as grown films
6.3.6 Variation of Optical
Bandgap
with Composition
6.3.7 D.C. Electrical
Resistivity
Measurements
6.4 Discussion
6.4.1 Structural Properties
6.4.2 Optical Properties 6.4.3 Electrical Properties
Chapter-VII Conclusion and future scope of work
54
55
55
56
56
56
57
57
57
58
58
60
References
67
List of Publications
76