A Study Into The Energy Gap Of A Semiconductor

Electrical Electronics Engineering | Industrial Physics | Physics

The energy gap of a semiconductor, often referred to as the band gap, stands as a fundamental characteristic determining its electrical properties. This critical parameter signifies the energy difference between the valence band, where electrons are tightly bound, and the conduction band, where electrons are free to move and conduct electricity. In the realm of semiconductor physics, this energy gap plays a crucial role in influencing the material’s conductivity and electronic behavior. A smaller band gap corresponds to a more conductive material, while a larger one results in a semiconductor with better insulating properties. Understanding and manipulating the energy gap of semiconductors is pivotal in the design and optimization of electronic devices, enabling the precise control of their electrical conductivity and performance. Researchers continually explore innovative ways to tailor this semiconductor characteristic for diverse applications, such as in the development of efficient solar cells, transistors, and other electronic components.

Inside a semiconductor, in order for the electrons to transition from the valence band to the conduction band, those electrons must be able to overcome an energy barrier called the energy gap or the band gap. Determine the energy gap of a certain semiconductor, assuming that the electric conductivity of the semiconductor only increase when it is heated.

An experiment on how to find the energy gap of the semiconductor was carried out using isothermal heating method using semiconducting diode with heating on temperature 40°C, 60°C, 80°C and 100°C gradually which can be used in educational process.

 

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

  • PROJECT OBJECTIVES
  • SCOPE OF THE PROJECT
  • SIGNIFICANCE OF THE STUDY
  • APPLICATION OF SEMICONDUCTOR
  • ADVANTAGES OF SEMICONDUCTOR DEVICES
  • DISADVANTAGES OF SEMICONDUCTOR DEVICES

CHAPTER TWO

LITERATURE REVIEW

  • OVERVIEW OF SEMICONDUCTOR
  • SEMICONDUCTOR DEVICE MATERIALS
  • PROPERTIES OF SEMICONDUCTOR
  • SEMICONDUCTOR MATERIALS
  • PREPARATION OF SEMICONDUCTOR MATERIALS
  • HISTORICAL BACKGROUND OF SEMICONDUCTORS

CHAPTER THREE

INTRODUCTION

  • INTRODUCTION
  • THEORETICAL PART
  • EXPERIMENT OF THE STUDY

 

CHAPTER FOUR

4.1     RESULT AND DISCUSSION

CHAPTER FIVE

  • CONCLUSION
  • REFERENCES

 

 

CHAPTER ONE

1.0                                                 INTRODUCTION

1.1                                              BACKGROUND OF THE STUDY

Semiconductors are defined by their unique electric conductive behavior, somewhere between that of a conductor and an insulator. The differences between these materials can be understood in terms of the quantum states for electrons, each of which may contain zero or one electron. These states are associated with the electronic band structure of the material. Electrical conductivity arises due to the presence of electrons in states that are delocalized, however in order to transport electrons a state must be partially filled, containing an electron only part of the time. If the state is always occupied with an electron, then it is inert, blocking the passage of other electrons via that state. The energies of these quantum states are critical, since a state is partially filled only if its energy is near the Fermi level

High conductivity in a material comes from it having many partially filled states and much state delocalization. Metals are good electrical conductors and have many partially filled states with energies near their Fermi level. Insulators, by contrast, have few partially filled states, their Fermi levels sit within band gaps with few energy states to occupy. Importantly, an insulator can be made to conduct by increasing its temperature: heating provides energy to promote some electrons across the band gap, inducing partially filled states in both the band of states beneath the band gap (valence band) and the band of states above the band gap (conduction band). An intrinsic semiconductor has a band gap that is smaller than that of an insulator and at room temperature significant numbers of electrons can be excited to cross the band gap.

A pure semiconductor, however, is not very useful, as it is neither a very good insulator nor a very good conductor. However, one important feature of semiconductors is that their conductivity can be increased and controlled by doping with impurities and gating with electric fields. Doping and gating move either the conduction or valence band much closer to the Fermi level, and greatly increase the number of partially filled states.

Some wider-band gap semiconductor materials are sometimes referred to as semi-insulators. When undoped, these have electrical conductivity nearer to that of electrical insulators, however they can be doped (making them as useful as semiconductors). Semi-insulators find niche applications in micro-electronics, such as substrates for HEMT. An example of a common semi-insulator is gallium arsenide. Some materials, such as titanium dioxide, can even be used as insulating materials for some applications, while being treated as wide-gap semiconductors for other applications.

In solid-state physics, an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move within the crystal lattice and serve as a charge carrier to conduct electric current. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move in the solid; however, if some electrons transfer from the valence to the conduction band, then current can flow. Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors, while conductors either have very small band gaps or none, because the valence and conduction bands overlap.

The aim of this study is to determine the Energy Band Gap of a Semiconductor by using germanium diode

1.2                              AIM AND OBJECTIVE OF THE STUDY

The main aim of this work is to study the energy gap of a semiconductor. At the end of this study the following objectives shall be achieved:

  1. Energy gap of different semiconductors shall be known.
  2. The description of Conductors, Insulators and Semiconductors shall also be known.
  • Lastly, an experiment was performed with regard to the study.

1.3                                            SCOPE OF THE STUDY

Every solid has its own characteristic energy-band structure. This variation in band structure is responsible for the wide range of electrical characteristics observed in various materials. In semiconductors and insulators, electrons are confined to a number of bands of energy, and forbidden from other regions. The term “band gap” refers to the energy difference between the top of the valence band and the bottom of the conduction band. Electrons are able to jump from one band to another. However, in order for an electron to jump from a valence band to a conduction band, it requires a specific minimum amount of energy for the transition. The required energy differs with different materials. Electrons can gain enough energy to jump to the conduction band by absorbing either a phonon (heat) or a photon (light).

1.4                                    SIGNIFICANCE OF THE STUDY

Energy band gap differentiates the metals into conductor, insulator, semiconductor. Energy band gap is usually referred to the energy difference between the conduction band and the valence band.

This study has made us to understand the energy which required for the promotion of a valence electron that bound to an atom which become a “conduction electron”, that is free for moving within the “crystal lattice” and it also serves as the “charge carrier” to the conduct of electric current.

1.5                 APPLICATION OF SEMICONDUCTOR

Semiconductors are employed in the manufacture of various kinds of electronic devices, including diodes, transistors, and integrated circuits. Such devices have found wide application because of their compactness, reliability, power efficiency, and low cost.

1.6                ADVANTAGES OF SEMICONDUCTOR DEVICES

  1. As semiconductor devices have no filaments, hence no power is needed to heat them to cause the emission of electrons.
  2. Since no heating is required, semiconductor devices are set into operation as soon as the circuit is switched on.
  • During operation, semiconductor devices do not produce any humming noise.
  1. Semiconductor devices require low voltage operation as compared to vacuum tubes.
  2. Owing to their small sizes, the circuits involving semiconductor devices are very compact.
  3. Semiconductor devices are shock proof.
  • Semiconductor devices are cheaper as compared to vacuum tubes.
  • Semiconductor devices have an almost unlimited life.
  1. As no vacuum has to be created in semiconductor devices, they have no vacuum deterioration trouble.

1.7            DISADVANTAGES OF SEMICONDUCTOR DEVICES

  1. The noise level is higher in semiconductor devices as compared to that in the vacuum tubes.
  2. Ordinary semiconductor devices cannot handle as more power as ordinary vacuum tubes can do.

In high frequency range, they have poor responder.

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Energy Gap Of A Semiconductor:

The energy gap of a semiconductor is a fundamental concept in solid-state physics and semiconductor device engineering. It plays a crucial role in determining the electrical properties and behavior of semiconductors. To understand the energy gap, let’s delve into some basics of semiconductor physics.

Semiconductor Basics:

Semiconductors are materials that have electrical conductivity between that of conductors (such as metals) and insulators (such as glass). The conductivity of a semiconductor can be controlled by various factors, including temperature, doping, and applied voltage.

In a crystalline solid, like a semiconductor, the atoms are arranged in a regular, repeating pattern called a crystal lattice. This arrangement gives rise to energy bands, which are regions in energy space where electrons are allowed to exist. The two main types of energy bands in a semiconductor are the valence band and the conduction band.

  1. Valence Band: The valence band is the highest energy band that is completely filled with electrons at absolute zero temperature. Electrons in this band are tightly bound to the atomic nuclei of the semiconductor material.
  2. Conduction Band: The conduction band is the next higher energy band, which is empty at absolute zero temperature. Electrons in this band are not bound to any specific atom and are free to move throughout the crystal lattice.

Energy Gap:

The energy gap, also known as the bandgap, is the energy difference between the top of the valence band and the bottom of the conduction band. It represents the minimum energy required to promote an electron from the valence band to the conduction band, thereby allowing it to participate in conduction.

Energy Gap Diagram

Types of Semiconductors based on Energy Gap:

Semiconductors can be classified into two main types based on their energy gap:

  1. Intrinsic Semiconductors: Intrinsic semiconductors are pure semiconductor materials without any intentional impurities. The energy gap of intrinsic semiconductors typically ranges from about 0.1 eV to 3 eV. Examples include silicon (Si) and germanium (Ge).
  2. Extrinsic Semiconductors: Extrinsic semiconductors are semiconductor materials that have been intentionally doped with impurities to modify their electrical properties. These impurities introduce additional energy levels within the energy gap. Extrinsic semiconductors are further classified into two types based on the type of doping:a. N-Type Semiconductors: In n-type semiconductors, the majority charge carriers are electrons. This is achieved by doping the semiconductor material with donor impurities, which introduce additional energy levels closer to the conduction band. The energy gap in n-type semiconductors remains largely unchanged from that of the intrinsic semiconductor.

    b. P-Type Semiconductors: In p-type semiconductors, the majority charge carriers are “holes,” which are essentially vacancies in the valence band left by the absence of electrons. This is achieved by doping the semiconductor material with acceptor impurities, which introduce additional energy levels closer to the valence band. Similar to n-type semiconductors, the energy gap in p-type semiconductors remains largely unchanged.

Importance of Energy Gap:

The energy gap of a semiconductor has significant implications for its electrical properties and applications:

  1. Conduction Mechanism: The energy gap determines the mechanism by which a semiconductor conducts electricity. Intrinsic semiconductors conduct electricity through thermal excitation, where electrons are promoted from the valence band to the conduction band by absorbing thermal energy. Extrinsic semiconductors conduct electricity through the movement of majority charge carriers (electrons in n-type, holes in p-type) introduced by doping.
  2. Optoelectronic Applications: The energy gap also governs the optical properties of semiconductors. Semiconductors with smaller energy gaps are more transparent to lower-energy photons (e.g., infrared light), while those with larger energy gaps are transparent to higher-energy photons (e.g., visible or ultraviolet light). This property is exploited in various optoelectronic devices such as light-emitting diodes (LEDs), photodetectors, and solar cells.
  3. Device Design and Performance: The energy gap influences the design and performance of semiconductor devices. For example, in electronic devices such as diodes and transistors, the energy gap affects parameters like the forward voltage drop, breakdown voltage, and switching speed. In photonic devices, the energy gap determines the wavelengths of light that the device can absorb or emit.

Measurement of Energy Gap:

The energy gap of a semiconductor can be measured experimentally using various techniques, including:

  1. Optical Absorption Spectroscopy: This technique involves shining light of varying wavelengths onto the semiconductor material and measuring the absorbance. The energy gap can be determined from the onset of absorption, corresponding to the minimum photon energy required to excite electrons across the energy gap.
  2. Electrical Conductivity Measurement: The energy gap can also be inferred from the temperature dependence of the electrical conductivity of the semiconductor. Intrinsic semiconductors exhibit a characteristic increase in conductivity with temperature due to thermal excitation across the energy gap.
  3. Photoluminescence Spectroscopy: Photoluminescence spectroscopy involves exciting the semiconductor material with light and measuring the emitted photons. The energy gap can be determined from the energy of the emitted photons, which corresponds to the energy difference between the conduction and valence bands.

Conclusion:

In summary, the energy gap of a semiconductor is a fundamental property that governs its electrical and optical behavior. It plays a crucial role in determining the conduction mechanism, optoelectronic properties, and device performance. Understanding the energy gap is essential for the design and optimization of semiconductor devices for a wide range of applications, from electronics to photonics