ELECTRICAL CONDUCTION THROUGH MATERIALS

Introduction

Electrical conduction is the movement of charged particles, such as electrons or ions, through a material in response to an electric field. In electronic materials, such as metals, semiconductors, and insulators, the nature of electrical conduction is determined by the properties of the material and its structure.

In metals, conduction is due to the presence of free electrons that are loosely bound to the atomic nuclei and can move easily in response to an electric field. These free electrons form a “sea” of mobile charge carriers that can conduct electricity through the metal. The electrical conductivity of metals is typically high, due to the abundance of free electrons.

In semiconductors, the behavior of electrical conduction is more complex. Pure semiconductors, such as silicon and germanium, have a small number of free electrons and holes, which are vacancies where an electron is missing. These can conduct electricity, but the conductivity is much lower than in metals. However, by introducing impurities or dopants into the semiconductor, the number of free electrons or holes can be increased, leading to higher conductivity.

In insulators, such as ceramics or plastics, the electrical conductivity is very low because there are no free electrons available to conduct electricity. However, in some insulators, such as certain types of polymers, there can be a type of conduction called ionic conduction, which occurs through the movement of ions rather than electrons.

Overall, the behavior of electrical conduction through electronic materials is determined by the properties of the material, including its crystal structure, electronic band structure, and doping level, as well as the presence of impurities or defects that can affect the movement of charged particles.

 

The behavior of conductors, semiconductors, and insulators can be explained through the concept of band theory, which describes the distribution of electrons within the energy bands of materials.

In a conductor, the valence band (the band that contains the outermost electrons) and the conduction band (the band immediately above the valence band) overlap, allowing electrons to move freely and conduct electricity. This overlap is due to the low energy gap between the two bands.

In contrast, in an insulator, there is a large energy gap between the valence band and the conduction band, which makes it difficult for electrons to move from the valence band to the conduction band. As a result, insulators are poor conductors of electricity.

Semiconductors have a small energy gap between the valence band and the conduction band, which allows electrons to move from the valence band to the conduction band when energy is supplied, such as through heat or the application of an electric field. This makes them intermediate in their ability to conduct electricity.

Furthermore, the behavior of semiconductors can be altered by introducing impurities or doping them with certain atoms. This changes the number of electrons or holes (absence of electrons in the valence band) in the material, allowing for the control of conductivity and other properties, making them ideal for electronic applications.

 

Silicon and germanium are two of the most commonly used semiconductor materials in the electronics industry. Both are members of the group IV elements in the periodic table and have four valence electrons in their outermost shell, which makes them good candidates for semiconductors.

Silicon is the most widely used semiconductor material, accounting for over 90% of the semiconductor market. It has a bandgap energy of 1.12 electron volts (eV) which means that it requires about 1.12 eV of energy to excite an electron from its valence band to the conduction band, making it ideal for use in electronics such as transistors, diodes, and solar cells. Silicon is also abundant, inexpensive, and has good thermal stability.

Germanium, on the other hand, has a bandgap energy of 0.67 eV, which means that it requires less energy to excite an electron than silicon. However, germanium is not as widely used as silicon due to its higher cost and lower thermal stability. Germanium is used in some specialized applications such as infrared detectors, high-speed switching devices, and some types of diodes.

Both silicon and germanium are used in the production of integrated circuits (ICs) which are the building blocks of modern electronics. The ability to control the properties of these materials through doping (intentional introduction of impurities) allows for the creation of p-type and n-type semiconductors, which form the basis of many electronic devices.

 

Intrinsic semiconductors are materials that have an equal number of electrons and holes, making them electrically neutral under normal conditions. They are pure and undoped semiconductors, meaning they do not contain any intentional impurities or dopants to alter their electrical properties.

Intrinsic semiconductors such as silicon and germanium have a band gap between their valence band and conduction band that is small enough to allow for some electrons to be excited from the valence band to the conduction band at room temperature. This creates a small number of free electrons and holes that can move and conduct electricity.

Intrinsic semiconductors are important in the field of electronics as they form the basis of many electronic devices such as diodes and transistors. Their electrical properties can be modified by introducing impurities or dopants, which can increase their conductivity or create p-type or n-type semiconductors.

 

Extrinsic semiconductors are materials that have been intentionally doped with impurities to increase their electrical conductivity. The doping process introduces impurities into the crystal lattice of the semiconductor, creating charge carriers that are either positively or negatively charged. These charge carriers are responsible for the conductivity of the material.

Doping is the intentional introduction of impurities into a semiconductor material to alter its electrical properties. There are two types of extrinsic semiconductors: p-type and n-type.

P-type semiconductors are created by doping the semiconductor material with impurities that have fewer valence electrons than the atoms in the semiconductor material. These impurities are called acceptors because they accept electrons from the valence band of the semiconductor material, leaving behind “holes” in the valence band. These holes can be thought of as positively charged charge carriers that contribute to the conductivity of the material.

N-type semiconductors are created by doping the semiconductor material with impurities that have more valence electrons than the atoms in the semiconductor material. These impurities are called donors because they donate electrons to the conduction band of the semiconductor material, creating negatively charged charge carriers that contribute to the conductivity of the material.

In both p-type and n-type semiconductors, the concentration of dopant atoms determines the conductivity of the material. The higher the concentration of dopant atoms, the higher the conductivity of the material.

 

A junction diode is a semiconductor device consisting of a p-type material and an n-type material that are joined together to form a junction. When a forward voltage is applied to the diode, current flows easily through the junction, and the diode is said to be forward biased. When a reverse voltage is applied to the diode, current cannot flow easily through the junction, and the diode is said to be reverse biased.

When a forward voltage is applied to the diode, the p-type material becomes positively charged and the n-type material becomes negatively charged. This creates a depletion region at the junction between the two materials where there are no free charges. If the applied voltage is large enough, it can overcome this depletion region and allow current to flow through the diode.

The voltage-current characteristics of a junction diode are nonlinear. At low voltages, the current through the diode is very small, but as the voltage increases, the current increases rapidly. This is known as the forward-bias region of the diode. The forward voltage at which the current begins to increase rapidly is called the threshold voltage, and it is typically around 0.7 volts for silicon diodes.

In the reverse-bias region, the current through the diode is very small until the reverse voltage reaches a certain value, known as the breakdown voltage. At this point, the current through the diode increases rapidly, and the diode can be damaged if the voltage is not limited. The reverse voltage at which the breakdown occurs depends on the material and the doping concentration of the diode.

Overall, junction diodes are widely used in electronic circuits for their ability to conduct current in one direction while blocking current in the opposite direction. They have many applications, such as in rectifiers, voltage regulators, and signal detectors.

 

Diodes are electronic components that allow the flow of electrical current in one direction while blocking it in the opposite direction. This property makes them useful for a wide range of applications, including rectification.

Rectification is the process of converting alternating current (AC) into direct current (DC). This is important because many electronic devices require DC power to operate, while the power grid delivers AC power. There are two types of rectification that are commonly used: half-wave rectification and full-wave rectification.

Half-wave rectification uses a single diode to allow current to flow in only one direction. The result is that half of the AC waveform is removed, leaving only the positive or negative portion of the waveform. This produces a pulsating DC waveform that is not very smooth, but it can be useful in some applications, such as powering LEDs or charging batteries.

Full-wave rectification uses four diodes arranged in a specific configuration called a bridge rectifier. This allows the entire AC waveform to be used, resulting in a smoother DC waveform with less ripple. This is important for applications that require a steady and reliable source of DC power, such as powering electronic devices or charging capacitors.

Overall, diodes are essential components for rectification and many other electronic applications, and the use of half-wave and full-wave rectification techniques allows for efficient and effective conversion of AC power into DC power.

 

In other words, Diodes are electronic components that allow current to flow in only one direction. They have various applications, including rectification. Rectification is the process of converting alternating current (AC) into direct current (DC) by allowing current to flow in only one direction.

There are two types of rectification: half-wave rectification and full-wave rectification. Both types of rectification use diodes, but they differ in the way they utilize them. Here are the uses of half-wave and full-wave rectification:

1) Half-Wave Rectification: In half-wave rectification, only one half of the AC waveform is allowed to pass through, while the other half is blocked. This is achieved by using a single diode. The output waveform obtained from half-wave rectification is not smooth and contains only half of the original AC waveform.

 

Uses

• Low Power Applications: Half-wave rectifiers are used in low power applications where a low voltage DC supply is required, such as in battery-powered devices like radios, flashlights, and small electronic gadgets.
• Signal Demodulation: Half-wave rectifiers are also used in signal demodulation, where the AC signal is converted into a DC signal to extract the original message signal. This application is commonly used in communication systems.

 

2) Full-Wave Rectification: In full-wave rectification, both halves of the AC waveform are used, but they are rectified separately. This is achieved by using either two diodes or a bridge rectifier. The output waveform obtained from full-wave rectification is smooth and contains the entire original AC waveform.

 

Uses

• High Power Applications: Full-wave rectifiers are used in high power applications where a high voltage DC supply is required, such as in power supplies for electronic devices and industrial machinery.
• Battery Charging: Full-wave rectifiers are also used in battery charging systems where AC voltage is rectified to produce a DC voltage for charging batteries. This application is commonly used in automobiles and other vehicles.

In conclusion, diodes are used in rectification circuits to convert AC to DC. Half-wave rectification is used for low-power applications and signal demodulation, while full-wave rectification is used for high-power applications and battery charging.