Semiconductors Properties Overview

Introduction

• Semiconductors are materials with electrical conductivity that falls between that of a conductor and an insulator.
• This intermediate conductivity allows them to be used in a wide variety of electronic devices.

Properties of Semiconductors

• Electrical conductivity: Can be controlled by factors like temperature, light, or the addition of impurities.
• Band structure: A defining feature is the presence of a band gap between the valence band (filled with electrons) and the conduction band (empty).
• Intrinsic semiconductors: Pure semiconductors, with minimal impurities.
• Extrinsic semiconductors: Semiconductors doped with impurities, altering their conductivity.
• Doping: Adding impurities to semiconductors to change their electrical properties.
  • N-type doping: Adding donor impurities (giving extra electrons).
  • P-type doping: Adding acceptor impurities (creating "holes" or missing electrons).
• Charge carriers: Electrons and holes are the charge carriers in semiconductors.
• Energy band gap: The energy difference between the valence band and conduction band; crucial for semiconductor device operation.
• Temperature dependence: Conductivity increases with temperature because more electrons gain sufficient energy to jump across the band gap.
• Carrier concentration: The number of charge carriers (electrons and holes) in a semiconductor.

Types of Semiconductors

• Silicon (Si): The most common semiconductor material due to its abundance, relatively low cost, and good performance in electronic devices.
• Germanium (Ge): Another important semiconductor material, but less prevalent than silicon.
• Gallium Arsenide (GaAs): A key material in high-speed electronics and optoelectronics.
• Other materials: There are many other semiconductor materials with specific applications.

Applications of Semiconductors

• Transistors: Fundamental building blocks of modern electronics, used for amplifying and switching electronic signals.
• Integrated circuits (ICs): Complex circuits containing numerous transistors and other components on a small chip, enabling the miniaturization of electronic devices.
• Diodes: Used to control the direction of current flow, with critical applications such as rectifiers and LEDs.
• Photovoltaic cells: Convert light energy directly into electrical energy, forming the basis of solar panels.
• Light-emitting diodes (LEDs): Emit light when current flows through them, used extensively in displays and lighting applications.
• Sensors: Semiconductors are used in various types of sensors such as temperature, pressure, and light sensors.
• Memory devices: Used in RAM, ROM and flash memory.

Semiconductor Manufacturing

• Crystal growth: Producing high-quality semiconductor crystals is crucial for device performance. Many techniques exist for this.
• Doping: Precisely adding impurities creates the desired electrical properties.
• Photolithography: Creating patterns on the semiconductor surface at a microscopic level.
• Etching: Removing unwanted material.
• Metallization: Adding metal contacts for electrical connections.
• Packaging: Enclosing the semiconductor device in a protective package for integration into larger systems.

Key Concepts

• p-n junction: The boundary between p-type and n-type semiconductors, fundamental to diode and transistor operation.
• Depletion region: A region near the p-n junction where the mobile charges are depleted, creating a barrier to current flow.
• Forward bias: Applying voltage across the p-n junction in a way that reduces the barrier and allows current to flow.
• Reverse bias: Applying voltage in a way that enhances the barrier and minimizes current flow.
• Breakdown voltage: The voltage at which the p-n junction breaks down and allows excessive current flow.
• Mobility: How easily charge carriers travel through a material, dependent on the material's properties.

Advancements in Semiconductor Technology

• Continuous improvements in material quality, device miniaturization, and manufacturing processes drive advancements in electronics.
• Research and development in novel semiconductor materials have led to increased performance, efficiency, and wider applications, such as in optoelectronics.