Lecture 12: Electrical Properties Flashcards
What determines the electronic properties of a material?
The electronic properties depend on electrical conductivity, the identity of the charge carriers, and the crystal structure.
Define electrical conductivity.
Electrical conductivity (ฯ) is a measure of a materialโs ability to conduct an electric current, calculated by
๐=๐๐๐, where ๐ is the number of charge carriers, ๐ is the charge on each carrier, and ๐ is their mobility.
What are the characteristics of a conductor?
Conductors have a significant portion of delocalized valence electrons that can freely move throughout the structure, facilitating electrical conductivity.
Explain the difference between intrinsic and extrinsic semiconductors.
Intrinsic semiconductors have electrical conductivity based on pure material properties, while extrinsic semiconductors have conductivity enhanced by doping with impurities.
What is the band gap in semiconductors?
The band gap is the energy difference between the valence band and the conduction band; its size determines a materialโs electrical conductivity and optical properties.
Define photoconductivity.
Photoconductivity is a phenomenon where a materialโs conductivity increases upon exposure to electromagnetic radiation, as electrons are excited from the valence band to the conduction band.
What is the significance of the band gap of CdS in solar cells?
CdS has a band gap of 2.5 eV, allowing it to absorb blue visible light, making it useful in solar cells for converting sunlight into electricity.
Describe the role of phonons in electrical conductivity.
Phonons, or lattice vibrations, interact with electrons, which can lead to scattering and resistance, affecting a materialโs electrical conductivity.
What is a dielectric material?
Dielectric materials are insulators that can be polarized by an electric field, which makes them important in applications like capacitors.
Explain the Lever Rule in the context of phase diagrams.
The Lever Rule is a tool used to determine the proportions of different phases in a binary phase diagram based on the overall composition of the system.
What does the term โband bendingโ refer to?
Band bending occurs when there is a spatial variation in the band edges within a semiconductor, often due to external influences like electric fields or junctions.
Define a p-n junction.
A p-n junction is a boundary or interface between p-type and n-type semiconductors, crucial for semiconductor-based electronic devices.
What are the electrical properties of p-type and n-type semiconductors?
P-type semiconductors have an abundance of holes (positive charge carriers), while n-type semiconductors have an excess of electrons (negative charge carriers).
How does doping affect the properties of semiconductors?
Doping introduces impurities into a semiconductor, which can provide extra electrons or holes to enhance conductivity.
What is an LED and how does it work?
An LED (Light Emitting Diode) is a semiconductor device that emits light when electric current flows through it, due to electron-hole recombination releasing energy in the form of photons.
Describe how the band gap influences LED color.
The color of the LED light depends on the band gap energy; different materials with different band gaps emit photons of varying energies, corresponding to different colors.
What is the difference between direct and indirect band gaps?
In direct band gap semiconductors, electron transitions between the valence and conduction bands occur vertically in momentum space, facilitating efficient light emission. In indirect band gaps, these transitions also involve a change in momentum, requiring a phonon to conserve momentum, which is less efficient for light emission.
How do transistors amplify electrical signals?
Transistors control a large current between the output terminals by a smaller current or voltage at the input terminal, allowing them to act as amplifiers.
What is a MOSFET?
MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a type of transistor that uses an electric field to control the conductivity of a channel in a semiconductor material.
Explain the function of CMOS technology in digital circuits.
CMOS (Complementary Metal-Oxide-Semiconductor) technology uses a pair of p-type and n-type MOSFETs to create logic gates that are highly effective in digital circuits due to low power consumption and high speed.
What role do semiconductors play in computers?
Semiconductors form the foundation of modern electronics, including transistors, diodes, and integrated circuits, which are essential components of computers.
Describe the concept of ferroelectric materials.
Ferroelectric materials have spontaneous electrical polarization that can be reversed by the application of an external electric field, similar to ferromagnetism in magnetic materials.
How do ion conductors differ from electronic conductors?
Ion conductors allow ions to move freely through the material, which is crucial in applications like batteries and fuel cells, whereas electronic conductors allow electrons to move freely.
What is piezoelectricity?
Piezoelectricity is the electric charge that accumulates in certain solid materials in response to applied mechanical stress.
