BeginnerTopic 1 of 104Electronics & Embedded
Atoms and energy bands
Electrons occupy bands; the gap between valence and conduction bands determines conductivity.
In depth
Electrons in solids occupy energy bands separated by gaps. The valence band is filled, the conduction band carries current. In metals the bands overlap, in insulators the gap is large, in semiconductors small (Si 1.12 eV). Temperature or light can excite electrons across the gap, creating electron-hole pairs.
Key points
- Band gap sets conductivity and colour of LEDs
- Fermi level indicates occupancy
- Holes behave as positive carriers
ExampleSilicon absorbs photons above 1.12 eV, which is why it makes solar cells.
What is Atoms and energy bands?
Electrons occupy bands; the gap between valence and conduction bands determines conductivity.
Why is it important to understand atoms and energy bands?
Whether a material conducts depends on how its electron energy levels are arranged, which is the physical reason transistors and diodes exist at all.
What is a band gap in simple terms?
It is the energy an electron needs to jump from a bound state to a state where it can move freely. Silicon has about 1.1 eV, enough to make a useful switch.
Why do metals conduct so well?
Their valence and conduction bands overlap, so electrons can move freely without any energy gap to cross.
How is Atoms and energy bands used in practice?
Typical applications include explaining why silicon is a semiconductor while copper is a conductor, choosing a material for an LED based on its band gap and colour and predicting how a chip's leakage current rises when it gets hot.
What should I learn before Atoms and energy bands?
It is the first topic in Electronics & Embedded, so no earlier topic in this course is required.
What are the key points of Atoms and energy bands?
Band gap sets conductivity and colour of LEDs. Fermi level indicates occupancy. Holes behave as positive carriers.
Can you give an example of Atoms and energy bands?
Silicon absorbs photons above 1.12 eV, which is why it makes solar cells.
What comes after Atoms and energy bands?
The next topic is "Intrinsic and extrinsic semiconductors", which builds directly on this one.
How difficult is Atoms and energy bands?
It is classed as Beginner in Electronics & Embedded (topic 1 of 104). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.