Introduction to Electronics by V K Mehta

Introduction to Electronics

• Electronics is the branch of physics and engineering concerned with the design of circuits using transistors and microchips, and with the behavior and movement of electrons in a semiconductor, conductor, vacuum, or gas.
• Electronics is also the science of how to control electric energy.
• Basic electronic components include resistors, capacitors, inductors, transformers, diodes, transistors, and integrated circuits.

Resistance

• The resistance of a material is the opposing force that a flowing charge encounters.
• All materials have a resistance that is dependent on cross-sectional area, material type, and temperature.
• A resistor dissipates power in the form of heat.
• A resistor in an electronic circuit can be in series, parallel, star, or delta.

Capacitor

• A capacitor is used to store charge for a short amount of time.
• A capacitor is a device that stores energy in an electric field, consisting of two conductive plates separated by a non-conductive material.
• Capacitors are rated by the amount of charge that can be held (in Farad) and the voltage handling capabilities.

Semiconductors

• Semiconductors are classified into two types: intrinsic and extrinsic.
• Intrinsic semiconductors contain no impurities and no crystalline defects.
• Extrinsic semiconductors are classified into two types: N-type and P-type.

N-type Semiconductors

• N-type semiconductors contain more electrons than holes.
• In an N-type semiconductor, conduction is mainly due to electrons (negative charges).
• Positive charges (holes) are the minority carriers.

P-type Semiconductors

• P-type semiconductors contain more holes than electrons.
• In a P-type semiconductor, conduction is mainly due to holes (positive charges).
• Negative charges (electrons) are the minority carriers.

Carrier Movement

• There are two mechanisms by which holes and free electrons move through a silicon crystal: drift and diffusion.
• Drift current is generated by the electrical field across a piece of silicon.
• Diffusion current is generated by the different concentration of carriers in a piece of silicon.

Silicon

• Silicon is a tetravalent element, which means it has four valence electrons and four vacancies.
• In intrinsic (pure) silicon, atoms join together by forming covalent bonds.
• Each atom shares its valence electrons with each of four adjacent neighbors, effectively filling its outer shell.

Electronic Properties of Si

• Silicon is a semiconductor material.
• Pure Si has a relatively high electrical resistivity at room temperature.
• There are two types of mobile charge-carriers in Si: electrons (negatively charged) and holes (positively charged).

Intrinsic Semiconductors

• A semiconductor is said to be intrinsic if it contains no impurities and no crystalline defects.
• The structure has zero overall charge.
• At absolute zero, every electron is at the lowest energy state, and the states in the conduction band are empty.
• Electrons leaving the VB to CB creates a vacancy called hole in the valence band.

Thermal Generation and Recombination

• At room or higher temperatures, electrons acquire thermal energy, which is transferred to them from the crystal lattice.
• Phonons can excite electrons from the valence band (VB) to the conduction band (CB).
• Electrons leaving the VB to CB creates a vacancy called hole in the valence band.
• The free electrons in the semiconductor can fall into holes in a process known as recombination.
• Energy is given up by the electrons in this process.