- Silicon Definition: Silicon is defined as a semiconductor with properties between those of a conductor and an insulator, crucial for electronics.
- Energy Bands in Silicon: Silicon has two main energy bands—conduction band and valence band—which determine its electrical properties.
- Forbidden Energy Gap: The forbidden energy gap is the energy difference between the conduction and valence bands, affecting whether a material is a metal, insulator, or semiconductor.
- Intrinsic Silicon: In intrinsic silicon, the Fermi level is in the middle of the energy gap, indicating pure silicon without impurities.
- Extrinsic Silicon: Energy bands in intrinsic and extrinsic silicon are altered by doping; adding donor atoms creates n-type silicon, while acceptor atoms create p-type silicon, shifting the Fermi level.
Silicon is a crystalline semiconductor whose electrical behaviour follows from its allowed electron-energy bands and the gap between them. A conductor has available states near its Fermi level, while an insulator has a much larger gap to mobile states. Silicon’s moderate band gap allows carrier concentration to be controlled by temperature, light, electric fields and doping. At 0 K in ideal intrinsic silicon, the valence band is full and the conduction band is empty.
Electrons thermally excited into the conduction band can move under an applied field, while the empty states they leave in the valence band behave as mobile holes. Both carriers contribute to current. The forbidden energy gap is the interval between the valence-band maximum and conduction-band minimum in which the perfect crystal has no allowed states.
Band occupancy and band gap together distinguish broad material classes. Metals have a partially filled band or overlapping bands; insulators have a large gap; and semiconductors have a smaller gap that permits a useful carrier population. Crystalline silicon has an indirect band gap of about 1.12 eV near 300 K, not 1.2 eV.
Covalent bonds join silicon atoms in the crystal. Thermal energy can promote a valence electron into the conduction band, creating an electron-hole pair. As temperature rises, intrinsic carrier concentration increases rapidly, although generation and recombination remain in equilibrium without external excitation.
Energy Band Diagram of Silicon
The energy band diagram of silicon plots allowed states against electron energy. In non-degenerate intrinsic silicon, the Fermi level lies close to midgap, with its exact position set by the conduction- and valence-band effective densities of states. Donor atoms introduce levels near the conduction band and shift the equilibrium Fermi level upward as n-type carrier concentration rises. Acceptor atoms introduce levels near the valence band and shift it downward in p-type material. Heavy doping, incomplete ionisation and temperature can change these simple relationships.
Energy Bands Diagram of Intrinsic Silicon
Energy Bands Diagram of Extrinsic Silicon
