UNIVERSITY OF NIGERIA, NSUKKA

FACULTY OF PHYSICAL SCIENCES

DEPARTMENT OF COMPUTER SCIENCE

TERM PAPER PREPARED WITH PARTIAL

FULFILLMENT TO THE COURSE
PHY 351 (ELECTRONICS)
ON
THE REVIEW ON RECENT RESEARCHES ON
SEMICONDUCTORS FROM 2019 – TILL DATE

BY

OGUH FRANKLIN EBUBECHUKWU

(2023/253810)

LECTURER: MR. OPARAKU EMEKA

JUNE, 2024

ABSTRACT
This document provides a comprehensive overview of semiconductors,
tracing their development from early studies by Michael Faraday in 1833 to
the production of the first silicon transistor in 1954, which marked the
dawn of the silicon electronics and microelectronics era. The introduction
of band theory and the focus on pure silicon and germanium growth
spurred extensive research in semiconductor technology, leading to its
pivotal role in modern electronics.
Semiconductors are materials with electrical conductivity between that of
conductors and insulators, essential for controlling electrical current in
electronic devices. Key properties such as the band gap and controlled
conductivity through doping are highlighted. The document categorizes
semiconductors into intrinsic and extrinsic types, explaining their
characteristics and the role of doping in enhancing their electrical
properties.
The formation and operation of P-N junctions, a fundamental component in
semiconductor devices, are described, along with their behavior under
forward and reverse biasing conditions. The wide array of applications for
semiconductors in modern technology is explored, including transistors,
integrated circuits, memory devices, microprocessors, and sensors.
Emerging semiconductor technologies, such as Gallium Nitride (GaN),
graphene-based semiconductors, organic semiconductors, Silicon Carbide
(SiC), quantum dots, and 2D materials, are discussed for their potential to
drive future advancements. The impact of semiconductor technology on
society is emphasized, highlighting its contributions to technological
advancements, healthcare, environmental sustainability, the automotive
industry, and enhanced connectivity and communication.

BRIEF HISTORY OF SEMICONDUCTORS

The development of studies in semiconductor materials is traced from its
beginnings with Michael Faraday in 1833 to the production of the first
silicon transistor in 1954, which heralded the age of silicon electronics and
microelectronics. Prior to the advent of band theory, work was patchy and
driven by needs of technology. However, the arrival of this successful
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quantum theory of solids, together with a concentration on the growth of
pure silicon and germanium and an understanding of their properties, saw
an explosion in activity in semiconductor studies that has continued to this
day.

WHAT ARE SEMICONDUCTORS?

A semiconductor is a material that has an electrical conductivity between
that of a conductor (metals) and an insulator (non-metals). This unique
property allows semiconductors to control the flow of electrical current,
making them essential in modern electronic devices.

PROPERTIES OF SEMICONDUCTORS
Band Gap:
 Semiconductors have an energy gap (band gap) between the valence
band (highest range of electron energies where electrons are
normally present at absolute zero temperature) and the conduction
band (lowest range of electron energies where electrons can move
freely).
 The size of the band gap determines the semiconductor's electrical
properties. For silicon, the band gap is about 1.1 eV.

Conductivity:
 Semiconductors have moderate conductivity, which can be precisely
controlled by adding impurities (a process called doping) or by
applying electric fields, light, or heat.

TYPES OF SEMICONDUCTORS
There are two major types of semiconductors: intrinsic semiconductors
and extrinsic semiconductors. We will explain them below:

1. INTRINSIC SEMICONDUCTORS

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 Intrinsic semiconductors are pure semiconductors with no intentional
impurities added. They are typically crystalline materials like silicon
(Si) or germanium (Ge).
CHARACTERISTICS OF INTRINSIC SEMICONDUCTORS:
 Band Structure: Intrinsic semiconductors have a well-defined band
gap between the valence band (VB), where electrons are bound to
atoms, and the conduction band (CB), where electrons are free to
move and conduct electricity when excited.
 Electrical Conductivity: At absolute zero temperature (0 K),
intrinsic semiconductors behave as insulators because all electrons
are in the valence band. As temperature increases, some electrons
gain enough energy to move to the conduction band, creating
electron-hole pairs and increasing conductivity.
 Carrier Concentration: The number of electrons in the conduction
band is equal to the number of holes (missing electrons in the
valence band) in intrinsic semiconductors.

2. EXTRINSIC SEMICONDUCTORS
Extrinsic semiconductors are semiconductors intentionally added
impurities to modify their electrical properties, this process is known as
Doping. There are of two types.

TYPES OF EXTRINSIC SEMICONDUCTORS:

 N-Type Semiconductors:
These semiconductors are doped with pentavalent impurities
(elements) like; Arsenic (As) or Antimony (Sb). Here, extra electrons
are introduced into the crystal lattice, increasing the concentration of
negative charge carriers (electrons), these electrons are the majority
carriers, while holes are minority carriers. N-Type semiconductors
conduct electricity due to the movement of electrons.
 P-Type Semiconductors:
These Semiconductors are doped with trivalent impurities
(elements) like; boron (B), aluminum (Al), or gallium (Ga). The
resulting effect are "Holes" or positive charge carriers which are
introduced into the crystal lattice, as these elements create
deficiencies of electrons. Holes are the majority carriers, and

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 electrons (minority carriers). P-Type semiconductors conduct
electricity due to the movement of holes.

P-N JUNCTIONS
A P-N junction is a crucial component in semiconductors formed by joining
a P-type semiconductor and an N-type semiconductor within a single
crystal of semiconductor material. In circuit diagrams, a P-N junction is
represented as a diode symbol with an arrow pointing towards the N-type
material, indicating the direction of conventional current flow (from P to
N).
During the formation of the P-N junction, free electrons move from the
N-region to the P-region, where they combine with the holes near the
junction. This process creates a region of positive charges (pentavalent
ions) near the junction. In the P-region, as electrons combine with holes,
the P-region loses holes, and a layer of negative charges (trivalent ions)
forms near the junction. These two layers of positive and negative charges
form the following structures:
1. Depletion Region: Near the junction, there is a depletion region where
mobile charge carriers (electrons and holes) are depleted due to
diffusion and recombination. This region acts as a barrier to the flow of
majority carriers (electrons in N-type and holes in P-type) across the
junction.
2. Built-in Potential: The junction develops a built-in potential due to the
diffusion of charge carriers, creating an electric field that opposes
further diffusion. This potential results in a barrier potential (typically
around 0.7 volts for silicon) that must be overcome for current to
conduct.

Operations in a P-N Junction (Biasing):

 Forward Biasing:

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 This is applying a positive voltage to the P-type material and a
negative voltage to the N-type material reduces the width of the
depletion region. This reduction allows majority carriers (electrons
in N-type and holes in P-type) to move across the junction, facilitating
current flow. In the forward bias condition, the junction behaves like
a low-resistance conductor, similar to a closed switch.
 Reverse Biasing:
This is applying a negative voltage to the P-type material and a
positive voltage to the N-type material widens the depletion region.
This widening further blocks the flow of majority carriers across the
junction. In this condition, the junction behaves like an insulator or
an open switch, allowing only a very small leakage current due to
minority carrier movement.
USES OF SEMICONDUCTOR IN MODERN TECHNOLOGIES
Semiconductors are used in a wide array of materials, devices, and
technologies. In this section, we will explore only a few of them:
1. Transistors: These are the essential building blocks of
semiconductor devices. They function to amplify or switch electronic
signals and come in different types, including field-effect transistors
(FETs) and bipolar junction transistors (BJTs).
2. Integrated Circuits (ICs): These are complex assemblies containing
millions or even billions of transistors, capacitors, and resistors on a
single chip. ICs are crucial for the functionality of modern electronic
devices, performing tasks such as logic operations, signal processing,
and power management.
3. Memory Devices: Semiconductor memory, such as dynamic
random-access memory (DRAM) and flash memory, is vital for data
storage and retrieval in electronic devices. These memory types are
essential for both temporary and long-term data storage in
computers, smartphones, and other electronics.
4. Microprocessors: Serving as the brain of computing devices,
microprocessors are advanced ICs that execute complex instructions,
enabling the functionalities of computers, smartphones, and other
digital devices. They integrate various components like the

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 arithmetic logic unit (ALU), control unit, and registers to perform
computing tasks efficiently.
5. Sensors: Semiconductor sensors are crucial for detecting and
converting physical parameters (such as light, temperature, and
pressure) into electrical signals. These sensors are integral to a wide
range of applications, from automotive systems to consumer
electronics.

EMERGING SEMICONDUCTORS TECHNOLOGIES AND

THEIR APPLICATIONS
Emerging semiconductor technologies are paving the way for significant
advancements across various applications. Here are some of the key
technologies and their applications:
1. Gallium Nitride (GaN) Semiconductors:
GaN semiconductors are being increasingly used in power electronics,
particularly in high-frequency and high-power applications such as RF
amplifiers, radar systems, and satellite communications. They offer
advantages like higher efficiency, smaller size, and lower power
consumption compared to traditional silicon-based devices.
2. Graphene-Based Semiconductors:
Graphene, a single layer of carbon atoms, shows promise in electronic
and optoelectronic applications due to its high carrier mobility and
unique electrical properties. It is being researched for use in flexible
electronics, transparent conductive films, and potentially in high-speed
transistors and sensors.
3. Organic Semiconductors:
Organic semiconductors are used in organic light-emitting diodes
(OLEDs) for displays and lighting, as well as organic photovoltaic cells
(OPVs) for solar energy harvesting. These materials offer flexibility,
lightweight properties, and the potential for low-cost manufacturing
processes.
4. Silicon Carbide (SiC) Semiconductors:
SiC semiconductors are increasingly used in power electronics,
particularly in high-temperature and high-voltage applications. They are
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 found in electric vehicles (EVs), renewable energy systems (solar
inverters, wind turbines), and industrial motor drives due to their
ability to operate at higher temperatures and voltages than silicon
devices.
5. Quantum Dots:
Quantum dots are nanoscale semiconductor particles that exhibit
quantum mechanical properties. They are used in display technologies
(QLED TVs) for their ability to emit pure and bright colors, in biomedical
imaging for fluorescence labeling, and potentially in quantum computing
for qubits.
6. 2D Materials (e.g., mos2, WS2):
These materials exhibit unique electronic properties due to their
ultrathin nature and quantum confinement effects. They are being
explored for applications in flexible electronics, sensors, and next-
generation transistors that could surpass the performance limitations of
traditional silicon-based devices.
IMPACT OF SEMICONDUCTOR TECHNOLOGY ON THE SOCIETY
Semiconductors have had a profound impact on society, influencing
numerous aspects of daily life and driving advancements in various
industries. Here are some key areas where semiconductors have made a
significant impact:
1. Advancements in Technology:
Semiconductors are the backbone of modern electronic devices. They
have enabled the development of advanced technologies in
computing, telecommunications, and consumer electronics.
Innovations such as smartphones, laptops, and wearable devices are
all powered by semiconductor technology.
2. Healthcare Improvements:
In healthcare, semiconductors play a critical role in the development
of medical devices and diagnostic tools. Technologies such as MRI
machines, CT scanners, and portable diagnostic devices rely heavily
on semiconductor components to function effectively.
3. Environmental Sustainability:

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 Semiconductors are crucial in the renewable energy sector. They are
used in solar cells for converting solar energy into electricity and in
the development of efficient battery technologies for energy storage.
These advancements help reduce reliance on fossil fuels and promote
the use of sustainable energy sources.
4. Automotive Industry:
The automotive industry has seen significant transformations due to
semiconductor technology. Modern vehicles are equipped with
numerous semiconductor-based systems, including advanced driver-
assistance systems (ADAS), infotainment systems, and electric
powertrains. This integration has led to safer, more efficient, and
environmentally friendly vehicles.
5. Enhanced Connectivity and Communication:
Semiconductors have revolutionized the way we communicate,
enabling the development of the internet, mobile networks, and
wireless communication technologies. This connectivity has
facilitated the growth of the digital economy, remote work, and
global collaboration.

CONCLUSION
In conclusion, the evolution of semiconductor technology from its inception
with Michael Faraday's discoveries to the modern era of silicon electronics
has revolutionized the way we live and interact with technology.
Semiconductors, with their unique ability to control electrical conductivity,
form the backbone of countless electronic devices that drive innovation in
various fields. By understanding the fundamental properties, types, and
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functions of semiconductors, we gain insight into their critical role in
everything from basic electronic components to sophisticated integrated
circuits.
The continuous advancement of semiconductor materials and technologies,
including emerging fields like GaN, graphene, and 2D materials, promises
further breakthroughs that will enhance device performance, efficiency,
and capabilities. These advancements not only fuel technological progress
but also address global challenges in energy sustainability, healthcare, and
connectivity.
In summary, the study and application of semiconductors have had a
profound impact on modern society, enabling the development of a wide
range of technologies that improve our daily lives. As research and
innovation in semiconductor technology continue to evolve, we can
anticipate even greater contributions to various industries and a deeper
integration into the fabric of our digital and connected world.

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development, and commercialization - Nanoscale, 2020.
Quantum Dot Optoelectronic Devices: Progress and Challenges -
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IEEE Journal of Solid-State Circuits: Ongoing publication, with articles from
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Wikipedia: Comprehensive overview of semiconductors and their types.
(Article is continually updated; last accessed June 2024)
Britannica: Detailed articles on various semiconductor types and their
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