Semiconductors Flashcards
What are the electrical properties of metals, insulators, and semiconductors?
Metals: Good electrical conduction.
Insulators: Encapsulate circuits to protect from the environment.
Semiconductors: Sometimes conduct electricity; can change from poor to excellent conductors.
What is electrical conductivity?
Conductivity is the ease with which electric charge carriers move through a material.
Electrical conductivity and resistivity are reciprocals of each other.
Resistivity is a fixed constant of a material.
How do energy bands form in hydrogen atoms?
When two hydrogen atoms come close, their energy levels form a lower energy level with two electrons of opposite spins.
How do energy levels behave in solids, like carbon?
In carbon, 2S and 2P electrons merge as atoms come closer, splitting into valence and conduction bands.
Electrons fill the valence band from the bottom up.
States below the valence band’s top are filled, while states above the conduction band’s bottom are empty.
What are the differences in band structures for metals, insulators, and semiconductors?
Metals: Empty states allow electrons to move freely.
Insulators: Large bandgap; electrons need high temperatures to reach the conduction band.
Semiconductors: Small bandgap; insulators at room temperature but conductors at higher temperatures.
What is a hole in the context of semiconductors?
A hole is the vacancy of an electron in the valence band, treated as having a positive charge.
Effective mass refers to the electron’s mass under forces in a solid.
What are intrinsic semiconductors?
Perfect semiconductors with no carriers at 0K.
No impurities or defects.
Equal number of electrons and holes (exciting one electron to the conduction band creates one hole).
A photon can excite an electron if its energy exceeds the bandgap.
What are extrinsic semiconductors?
Formed by replacing one atom in the lattice with another.
N-doping: Replacing atom has an extra valence electron.
P-doping: Replacing atom has one less valence electron.
What are energy-momentum curves?
Electrons in the conduction band can be at rest or have momentum.
Electrons with momentum have more energy due to kinetic energy.
Energy-momentum relationships are shown in energy vs. momentum graphs.
What is carrier mobility?
Current flows when an electric field is applied to electrons, though electrons may scatter due to impurities or collisions.
Current equation: I = -qn⋅v (current depends on charge, number of electrons, and average velocity).
Mobility equation: μ = v/E (ease of movement of electrons in a material).
What do energy band diagrams represent?
Energy band diagrams plot energy vs. momentum.
Γ represents zero momentum.
