Introduction to Semiconductor Physics

Introduction to Semiconductor Physics

• Semiconductors are materials with electrical conductivity between that of a conductor and an insulator.
• Their conductivity can be modified substantially by adding impurities (doping), temperature changes, or exposure to light.
• This property makes them crucial in modern electronics.

Intrinsic Semiconductors

• Intrinsic semiconductors are pure, undoped materials.
• Electrons in the valence band can become free electrons in the conduction band through thermal excitation.

Extrinsic Semiconductors

• Extrinsic semiconductors are doped with impurities.
• Doping creates either extra electrons (n-type) or electron "holes" (p-type).
• N-type semiconductors have an excess of electrons.
• P-type semiconductors have an excess of holes (missing electrons).

Energy Band Diagram

• The energy band diagram illustrates the allowed energy levels for electrons in a material.
• The valence band is the highest completely filled energy band.
• The conduction band is the lowest partially filled or empty energy band.
• The energy gap (bandgap) separates the valence and conduction bands.
• The bandgap energy determines the material's electrical conductivity.

Carrier Concentrations

• The number of free electrons and holes in a semiconductor is described by carrier concentrations.
• These are influenced by temperature and doping concentration.
• Equilibrium carrier concentrations exist under stable conditions.
• Non-equilibrium carrier concentrations occur when external factors, like light or electric fields, disrupt the balance.

Doping Effects

• Doping with impurities can significantly alter the conductivity of semiconductors.
• Different doping concentrations create different levels of n-type or p-type conductivity.
• The doping level is critical to controlling the electrical properties of the semiconductor.

PN Junctions

• A PN junction is formed by the contact of p-type and n-type semiconductors.
• A depletion region forms at the junction, containing immobile ions.
• The depletion region acts as a barrier to current flow.
• PN junctions behave as diodes, allowing current in one direction only.

Semiconductor Devices

• Semiconductors are the basis for most modern electronic devices.
• Diodes, transistors, integrated circuits are examples of semiconductor devices.
• Diodes rectify alternating current.
• Transistors amplify or switch electronic signals.
• Integrated circuits (ICs) contain many transistors and other components on a single chip.

Impact of Temperature

• Increased temperature increases the number of free electrons and holes, increasing conductivity.
• At higher temperatures, the conductivity rises exponentially.

Impact of Light

• Light with sufficient energy can excite electrons from the valence band to the conduction band, increasing the conductivity (photoconductivity).
• This effect is used in photodetectors.

Types of Semiconductor Materials

• Silicon (Si) and Germanium (Ge) are common examples.
• Other materials, like Gallium Arsenide (GaAs), have specific applications due to their unique properties.

Applications of Semiconductors

• Microprocessors, memory chips, LEDs, solar cells, and many other modern technologies.
• Semiconductors are ubiquitous in modern electronics.

This quiz covers fundamental concepts in semiconductor physics, including intrinsic and extrinsic semiconductors. Understand the differences between n-type and p-type materials, and explore energy band diagrams. Perfect for students delving into the basics of electronics and material science.