semiconductor

Contents

  1. Semiconductor Diodes

    • 1.1 - 1.34 Unit 1

  2. Bipolar Junction Transistor (BJT)

    • 2.1 - 2.34

  3. MOSFET

    • 3.1 - 3.12

  4. Power Supply

    • 4.1 - 4.30

  5. Oscillators

    • 5.1 - 5.24

  6. Data Converters

    • 6.1 - 6.24

Sir Joseph John Thomson

  • Born: 18 December 1856 - Died: 30 August 1940

  • Profession: English Physicist and Nobel Laureate in Physics

  • Contributions:

    • Discovery of the electron, the first subatomic particle discovered.

    • In 1897, demonstrated that cathode rays were composed of negatively charged particles (termed electrons) with mass smaller than atoms.

    • Discovered first evidence for isotopes of stable elements in 1913 during research on canal rays.

    • Worked with Francis William Aston on mass spectrometry leading to the development of the mass spectrograph.

Semiconductor Basics

  • Definition: Semiconductor materials have electrical conductivity between conductors and insulators.

  • Common Materials: Include germanium (Ge), silicon (Si), selenium (Se), gallium arsenide (GaAs).

  • Temperature Effect: Semiconductors have a negative temperature coefficient of resistance; resistance decreases as temperature increases.

Types of Semiconductors

  • Intrinsic Semiconductors: Pure semiconductor materials without any impurities.

  • Extrinsic Semiconductors: Doped with impurities to enhance conductivity. Two types:

    • P-type: Contains acceptor impurities (produces holes).

    • N-type: Contains donor impurities (produces free electrons).

Formation of P-N Junction Diode

  • P-N Junction Formation:

    1. Involves the diffusion of p-type and n-type materials into a single crystal semiconductor.

    2. Doping Process: the addition of impurities to create extrinsic semiconductors.

  • Types of Diodes:

    • Rectifying Diode

    • Switching Diode

    • Zener Diode

    • LED

    • Photodiode

P-N Junction Structure

  • Diode Representation:

    • Symbol:

      • Anode (positive side) and Cathode (negative side).

  • Basic Working Principle: Allows current flow in one direction while resisting current flow in the opposite direction.

  • Depletion Region: Formed due to the recombination of electrons and holes at the junction when a p-n junction is formed.

Operating Principle of Diodes

Forward Bias

  • Conditions:

    • Anode connected to positive terminal and cathode to negative terminal of the power source.

  • Behavior:

    • Offers low resistance (acts as a closed switch).

    • Allows current to flow as potential barrier is overcome (knee voltage at approximately 0.7V for silicon).

Reverse Bias

  • Conditions:

    • Anode connected to negative terminal and cathode to positive terminal.

  • Behavior:

    • Offers high resistance (acts as an open switch).

    • Small leakage current might flow due to minority charge carriers.

I-V Characteristics of Diode

  • Importance: Understanding the current-voltage relationship is crucial for all semiconductor devices.

  • Graph Interpretation: A graph plotting current (Y-axis) against voltage (X-axis) provides insights into the dynamic resistance and operational behavior of the diode.

Zener Diodes

  • Construction: Heavily doped p-n junction, allows for tunneling of electrons under reverse bias.

  • Applications: Commonly used for voltage regulation due to their sharp breakdown voltage properties.

Light Emitting Diodes (LED)

  • Function: Convert electric energy into light energy when current flows through a forward-biased p-n junction.

  • Applications: Indicators, lighting, displays, etc. Color determined by semiconductor material used.

Photodiodes

  • Function: Used in reverse bias mode to generate current when exposed to light, signaling energy from photons.

  • Applications: Optical communication, burglar alarms, and various sensing applications.

Optocouplers

  • Composition: Contain LED and phototransistor enclosed within one package for signal isolation.

  • Applications: Electrical isolation, coupling in various circuits, used to cut down ground loops.

Solar Cells

  • Basic Principles: Convert sunlight into electrical energy through photovoltaic effect. Applications: Provide clean energy in various settings, from small electronic devices to large solar panels.

Technical Specifications to Consider for Diodes

  1. Forward Current (IF max)

  2. Reverse Current (IR max)

  3. Reverse Breakdown Voltage (PIV)

  4. Power Rating

Summary

  • Semiconductors bridge the conductivity gap between conductors and insulators.

  • Key semiconductor devices include diodes, BJTs, MOSFETs, and optocouplers, each with unique applications in electronics.

  • Understanding diode operation, characteristics, and applications assistance in designing effective electronic circuits.