Mada za sehemu hiiElectronicsMada 6
- The Band Theory of Solids
- Semiconductors
- Transistors
- Logic Gates
- Operational amplifiers
- Telecommunication
Introduction to energy bands
In isolated atoms, electrons occupy discrete energy levels (orbits). In solids, atoms are closely packed, causing the outer electrons' energy levels to overlap due to mutual interaction. These overlapping energy levels form energy bands: a range of allowed energies for electrons.
The valence band is the range of energy levels filled with valence electrons. It forms from the lowered energy levels after orbital interaction. Valence electrons are bound but can become free if excited.
The conduction band is a higher energy band where electrons are free to move, allowing electrical conduction. Valence electrons can be excited to this band by external energy (heat, electricity). Electrons in this band are called conduction electrons.
The energy gap between the valence band and conduction band where no electron can exist. Electrons require energy ≥ band gap to move to the conduction band. A larger band gap means electrons are more tightly bound to the atom.
| Material | Band Structure | Example |
|---|---|---|
| Conductors | Valence and conduction bands overlap (no band gap) | Copper, Aluminium |
| Semiconductors | Small band gap (e.g., Si = 0.7 eV, Ge ≈ 0.3 eV) | Silicon, Germanium |
| Insulators | Large band gap (5–15 eV); very little conduction | Glass, Mica, Wood |
The Fermi level is the energy level with a 50% probability of being occupied by an electron at a given temperature. In conductors, it lies within the overlapping bands. In semiconductors and insulators, it lies midway in the forbidden gap. Fermi Energy is defined at absolute zero (0 K) and refers to the highest occupied energy level.
| Material | Effect of Increasing Temperature |
|---|---|
| Conductors | Decreased conductivity due to more atomic vibration (resistance increases) |
| Semiconductors | Increased conductivity as more electrons jump to conduction band |
| Insulators | No significant change (band gap too large); may conduct only at high T |
| Superconductors | Perfect conductivity near absolute zero (0 K) |
Mwalimu
Unasoma somo hili? Niulize nikuelezee chochote kilichomo.
Ingia ili kumuuliza Mwalimu wa AI wa Sonza kuhusu mada hii.
Ingia ili kuuliza