A PROJECT REPORT
ON
FABRICATION AND CHARACTERISATION OF
SILICON NANOWIRES
The Project Submitted to the Utkal University Vanivihar, Bhubaneswar for the
Partial Fulfilment of the Degree of Bachelor
Submitted By:
SUSHREE ARPITA JENA
+3 3rd Year Science (6th Semester)
University Roll No:- 2102010730140035
Under the Guidance of:
Mr. Soumya Ranjan Dash
Lect. In Physics
DEPARTMENT OF PHYSICS
ANCHALIKA DEGREE MAHAVIDYALAYA,
PRANGYAN VIhar, Siminai
DHENKANAL, ODISHA
Session: 2021-24
Department of Physics
ANCHALIKA DEGREE MAHAVIDYALAYA
PRAGYAN VIHAR, DHENKANAL
CERTIFICATE
This certify that Miss. Sushree Arpita Jena, a student of the Department
of Physics at ANCHALIKA DEGREE MAHAVIDYALAYA,
PRAGYAN VIHAR, SIMNAI, DHENKANAL in +3 3rd year, Science
bearing the Roll No. BS(P)-21-032 has successfully completed and
submitted her project report with the topic “FABRICATION AND
CHARACTERISATION OF SILICON NANOWIRES” .
She is a bona fide student of this institution and the project has carried out
at our department under the supervision and guidance of expert personnel.
Mr. Soumya Ranjan Dash
Lect. In Physics
ACKNOWLEDGMENT
I wish to express my sincere gratitude to Mr. Dharanidhar Barik ,
Principal of ANCHALIKA DEGREE MAHAVIDYALAYA,
PRAGYAN VIHAR, SIMNAI, DHENKANAL, ODISHA for providing
me an opportunity to do my project work in “FABRICATION AND
CHARACTERISATION OF SILICON NANOWIRES” .
I sincerely thank to Mr. Soumya Ranjan Dash for his guidance and
encouragement in carrying out this project work. His concern for students
and consistent help throughout the period has drawn my keen interest and
helped in the successful completion of this project work.
I am thankful for my peers who have always been there for me when I need
them and would be happy to express my gratitude.
DECLARATION
I hereby declare that the project work entitled “ FABRICATION
AND CHARACTERISATION OF SILICON NANOWIRES”
submitted to ANCHALIKA DEGREE MAHAVIDYALAYA,
PRAGYAN VIHAR, SIMNAI, DHENKANAL is a record of
an original work done by me, and this project work is submitted in
the partial fulfillment of the requirements for the award of the
degree of Bachelor of Science in Physics. The results embodied
in this project have not been submitted to any other University or
institution for the award of any degree or diploma.
Sushree Arpita Jena
Roll No: BS(P)-21-032
University Roll No: 2102010730140035
CONTENTS
ABSTRACT
1. INTRODUCTION
1.1 MOTIVATION AND BACKGROUND
2. PROPERTIES OF SILICON BULK
3. PROPERTIES OF SEMICONDUCTOR NANOWIRES
4. APPLICATIONS OF SILICON NANOWIRES
5. LIGHT EMISSION FROM NANOSCALE SILICON
6. DIFFERENT TECHNIQUES FOR FABRICATION OF SILICON
NANOWIRES
6.1 VAPOUR LIQUID-SOLID (VLS) MECHANISM
6.2 CHEMICAL VAPOUR DEPOSITION (CVD) MECHANISM
6.3 MOLECULAR BEAM APITAXY MECHANISM
6.4 LASER ABLATION MECHANISM
6.5 AQUEOUS MECHANISM (ELECTROLESS CHEMICAL
ETCHING)
7. OBJECTIVE OF STUDY
8. FABRICATION OF SILICON NANOWIRES
9. CHARACTERISATION TECHNIQUES
9.1 X-RAY DIFFRACTION
9.2 SCANNING ELECTRON MICROSCOPE
9.3 9.3 TRANSMISSION ELECTRON MICROSCOPE (TEM)
10. RESULTS AND DISCUSSION
11. CONCLUSION
12. REFERENCES
ABSTRACT
In this project work Si nanowires were fabricated on the Si substrate by
aqueous method. In this aqueous method Ag is used for electroless chemical
etching. The precursors those were taken are AgNO3, HF and H2O2. Si
nanowires are fabricated at 55°C.
The samples were characterized by X-ray diffraction and scanning electron
microscope. Result shows morphology of the Si nanowires by scanning
electron microscope. X-ray diffraction confirms the phase Si. The XRD
analysis confirms the phase of silicon and crystalline nature of silicon .It is
found to be single crystalline with plane (1 0 0). The SEM study shows that
the particles were uniform and afterwards the non-uniformity arises. At 60
second of electroless deposition, the particles shape became anisotropic.
Some of the particles have grown vertically. This kind of non uniform
pattern can cause a non- uniform distribution of Silicon nanowires. It is
confirmed that the morphology of the nanowires also depends on the
resistivity of the wafers. The magnified HRTEM image shows the well-
resolved lattice spacing of the silicon nanowire, which depicts the crystalline
nature of the silicon nanowire.
Keywords: Fabrication, Silicon, Nanowires, Electroless Chemical Etching.
1.INTRODUCTION
1.1 MOTIVATION AND BACKGROUND
In the last years, there is an increasing demand of nanomaterials.
Nanomaterials are in the form of nanoparticles, nanowires, nanotubes. The
rising demand is because of its properties. Nanowires are also called as
quantum wires because of its dimension. Nanowires are of the diameter
nanometres range and length in the range of micrometres. Recently, there is
an increase in growing interest in the research work on Si nanowires because
of its application in many fields like optoelectronics, sensor field, and
photovoltaic applications. If Si nanowires can be used properly in
photovoltaic cells then it will be more efficient and can help in solving the
energy crisis. Transformation of bulk material to ductile material can be
done by the creation of dislocation and fostering dislocation motion at high
temperatures of about 2/3rd of melting point of bulk or phase
transformation at high pressure [1]. Understanding the atomic mechanisms
and dynamics of a brittle material impacted by an external force is
fundamentally important to theoretical and applied physics, such as atomic
lattice elastic-plastic response, brittle-ductile (BD) transition materials
toughness, hardness, and fractures. Currently, with the emergence of new
directions in flexible dimensionality of electronic devices and forms as well
as advancements in single nanowire (NW) electronics, it has become crucial
to assess the nanoscale mechanical responses such as elastic-plastic
deformation of the most important semiconductor materials, such as Si and
SiC [1,2]. Theoretical study reveals that recent developments in simulation
techniques have opened new approaches for investigating the microscopic
origins of complex nanomaterial phenomena. However, some results are
contradictive too i.e. brittle-fracture features with small strain were
observed by large atomic number molecular dynamics (MD) simulations for
Sic NWs [1,3].
On a contrary to that large strain elasticity and ductile fractures were
achieved. Yet, the important thing is experimental evidence which is
mandatory to clarify the true deformation features and mechanisms of the
ceramic nanowires. Simultaneous testing and nanoscale imaging makes
understanding of atomic scale features of NWs a big challenge. In particular,
with respect to the elastic plastic and B-D transitions, the physical picture
regarding the atomic scale mechanisms and dynamics of an individual NW
remains to be investigated. NWs are commonly utilized as a vibrating beam
in NEMS, because of their nature vibrating continuously at or near their
resonant frequency. Any small change in the local environment, such as
perturbations in forces, pressure or mass, can be detected by monitoring the
corresponding changes in the resonance frequency of the NWs. This
technique of nanowire-based NEMS has been successfully applied in atomic
force microscopy (AFM) and various kinds of sensors and actuators. There
are many semiconductor material systems which would be suitable for
fabrication of nanowire field effect sensors. Quite a few have been
demonstrated successfully, including silicon, silicon germanium, indium
oxide, tin oxide, gallium nitride, among others, and yet silicon stands out as
a clear favourite for the very same reason that the microprocessors in our
computers are crafted from silicon: microfabrication [1,3]. Silicon has
proved over and over again to be a practical and versatile material for
electronic devices. It does not have the high mobility or direct band gap of
III V compound semiconductors but it can be grown cheaply, has a stable
oxide, has reliable etchants, allows for good control over electronic
properties and can be fabricated on scale of very large wafers. Even in our
own lab, we tried several other material systems and growth methods before
settling on silicon as our material of choice Advances in the design, synthesis
and characterization of nano materials are expected to provide the
unprecedented ability to manipulate matter at the most fundamental level,
allowing the implementation of novel nanometre scale devices and systems
with unique properties and of utmost technological importance. Bottom up
growth has enabled researchers to demonstrate a myriad of nanostructures
of various material compositions and geometries. However, it remains a
challenge to turn some of these materials, which are admittedly exciting and
beautiful, into robust device technologies. Ultimately, nature seems to favor
bottom up organization and thus it is certainly a useful and noble task to
pursue. By using top down fabrication, on the other hand, the semiconductor
industry has demonstrated the ability to create billions of nanostructures on
a single square centimetre of silicon. In the rush to produce exciting end
results, the details are lost and ultimately the results are less understandable
and less compelling. In the case of bio sensing, where we must combine
aspects of solid state device physics and electrical engineering with
chemistry, biochemistry, and fluid mechanics it is difficult for one individual
to be fully versed in all the details. And yet to fully understand and
appreciate the complexity of the operation of nanowire sensors, it is
important to have a detailed understanding of the solid state physics,
chemistry, and mechanics that combine to produce a measurable effect [4].
To neglect any of these aspects necessarily leads to poor engineering
decisions and to poor science. As a result, we have tried to fully understand
our nanowires as semiconductor devices prior using them as sensors, and
then make use of this understanding to inform the ways in which we use the
sensors in light of what we know about biochemistry and fluid mechanics.
The result is hopefully a more complete, robust and usable system for bio
sensing. When the physical dimensions of a device are reduced to the
nanometerscale, quantum phenomena become prevalent modifying the
optical and electronic properties of the material. Therefore, it is of great
scientific interest to characterize the vibrational properties of NWs.
2.PROPERTIES OF SILICON BULK
Semiconductor devices are key components in modern electronic systems.
Silicon and gallium arsenide with its related III-V compounds form the basis
of the most commonly used semiconductor materials. However, silicon is by
far the major player in today's electronics market, dominating the
microelectronics industry with about 90% of all semiconductor devices sold
worldwide being silicon based. Silicon is a semiconductor material with the
band gap of 1.12eV. Silicon possesses two of the most outstanding natural
dielectrics, silicon dioxide (SiO2) and silicon nitride (Si3N4), which are
essential for device formation. In particular, SiO2, which is the basis of the
metal-oxide – semiconductor devices (MOS) can be grown thermally on a
silicon wafer, it is chemically very stable and can achieve a very high
breakdown voltage. The interface defects of the thermally grown SiO2 by
reaction of oxygen with a silicon wafer are several orders of magnitude lower
than those of any deposited film. Silicon is non-toxic, relatively inexpensive
(silicon comprises about 26% of the earth's crust which makes it second in
abundance only to oxygen), easy to process (a very well established industrial
infrastructure in silicon processing exists around the world), and has quite
good mechanical properties (strength, hardness, thermal conductivity,
etc.).For all the above reasons, silicon is the cornerstone material in
electronic systems. However, one of the most vital limitations of bulk silicon
is in optoelectronic applications, because of its inefficiency at emitting light
[4,5]. This is due to its indirect energy bandgap, which generally makes
optical transitions in the bulk material at room temperature a very rare
phenomenon. In a semiconductor with an indirect fundamental energy
bandgap, the maximum of the valence band and the minimum of the
conduction band are found at different locations in the k-space, therefore
energy required for transition is actually more than the bandgap.
Recombination by a single photon which possesses negligible momentum -
is not allowed, because of momentum conservation. Participation of a
phonon with the right momentum is necessary to satisfy momentum
conservation. Phonons are quantized modes of lattice vibrations that occur
in a solid. In the bulk material, this phonon assisted optical transition is very
weak, allowing many other non-radiative processes to dominate resulting in
a huge drop in the light emission efficiency. Bulk silicon is therefore not
suitable for the fabrication of optoelectronic devices. To date, the
semiconductor optoelectronics industry has been dominated by the III-V
compound semiconductors, because of their high efficiency in optical
transitions primarily due to their direct fundamental energy band-gap. It is
an intrinsic semiconductor. It has diamond shaped crystal structure. It is
very brittle and has marked metalloid luster. Its atomic number is 14 and
atomic mass is 28.08g mol-¹. Generally it is tetravalent in its compounds but
it can be bivalent sometimes. Its melting point is 1410°C and boiling
temperature is 3265°C.
Silicon is a refractory material
3.PROPERTIES OF SEMICONDUCTOR NANOWIRES
Nanowires are hair-like, one-dimensional (1D) nanomaterials with
diameters in the sub-one hundred nanometre scale and lengths ranging from
several hundreds of nm to as high as a few cm. Owing to their nanoscale
dimensions in the radial direction, they have size confinement effects that
give them novel physical properties as compared to bulk materials. Their
one dimensional geometry on the nanometerscale provides an extremely
high surface area with a nanoscale radius of curvature and great mechanical
flexibility with near theoretical strength. These properties are advantageous
in many chemical and mechanical applications. The geometry also Si
nanowires have greater surface to volume ratio than the Si bulk material. As
we go on reducing the size of Si bulk material the number of surface atom
increases. As the number of surface atoms increases its optical absorbance
also increases. That means optical absorbance of Si nanowires is more than
Si bulk material. The optical absorbance of Si nanowire is highest in larger
wavelengths. In UV and IR spectrum the reflectance of the Si nanowire is
less than 5%. Band gap is a function of the diameter of nanowires. So as the
size of the Si bulk material decreases its band gap increases. But the increase
in the band gap is very less, in decimals. For example a 3.2 nm diameter Si
nanowires has a band gap of 1.50 eV [15, 16, 17]. Melting point of the
material also depends on the size. As the size of the material reduces the
number of surface atoms increases and because of this the atoms have less
neighbouring atoms. Less neighbouring atoms result in less cohesive energy
among them. So less heat is required to break the bonds. So melting point of
the Si nanowire is less than Si bulk materials. As Si nanowires have greater
surface to volume ratio its surface reactivity is more provides anisotropic
properties that should be interesting from the point of view of nanomaterials
science and engineering. Their length, reaching as high as the cm scale,
makes them easy to manipulate for device fabrication. Nanowires are
promising materials for advanced optoelectronics. In addition to the unique
aspects of their physical, chemical, and mechanical properties, the size of
these materials is comparable to visible light in wavelength from 400 to 650
nm [18]. This implies that nanowires can be used to handle light on a
nanometre scale and thus can be used as building blocks for advanced
optoelectronics. Indeed, novel methods of the manipulation of light with
nanowires, including nanoscale Fabry-Perot mode stimulated emission,
wave guiding of photons, random lasing action, highly efficient
luminescence, and extremely sensitive photo-detection, have recently been
demonstrated. The concept of many advanced nanowire-based
optoelectronic devices including light-emitting diodes (LEDs).
4.APPLICATIONS OF SILICON NANOWIRES
Optical communications industrial growth has generated a high demand for
efficient and low-cost materials to be used for properties and functions such
as light emission, detection and modulation. Also, silicon based materials
with enhanced optical properties have applications in accelerating the
efficiency of photovoltaic solar cells, which is a market also dominated by
silicon, and which is expected to experience a tremendous growth in the near
future. The importance of developing a technology that would allow optical
and electronic devices to be easily integrated on a silicon wafer has long been
recognized. Over the past 15 years, considerable efforts have been carried
out within the research community for achieving this goal. Several materials
and methods have emerged out to be as possible contenders for silicon-based
optoelectronic devices and applications which includes silicon-based super
lattices and quantum dots facilitating quantum confinement in silicon
nanocrystals [3,4]; SiGe and SiGeC devices doped with optically efficient
rare earth impurities such as erbium direct integration of III-V materials on
silicon; porous silicon; silicon and carbon clusters embedded in oxide or
nitride matrices; super lattices of epitaxially grown silicon with adsorbed
oxygen. Most of the above mentioned techniques involve devices that are
based on nanoscale silicon. Electrons in the conduction band and holes in the
valence band are confined spatially by potential barriers in nanostructures.
Where as in quantum dots, carriers are confined in all three dimensions (3D
quantum confinement). In a nano-wire, the carriers are confined in two
dimensions and are free in only one dimension (2D quantum confinement).
In a super lattice, carriers are confined in only one direction and free to move
on the plane (ID quantum confinement). Such quantum confined super
lattices based on gallium arsenide (GaAs) and indium phosphide (InP) have
already found commercial applications in semiconductor distributed
feedback lasers (DFB), semiconductor optical amplifiers, and VCSELs for
optical communications [14, 15]. Basically, in all cases quantum confinement
pushes up the allowed energies effectively
