Intrinsic Semiconductor
Definition and meaning of Intrinsic Semiconductor in chemistry.
Intrinsic semiconductor is a chemically pure semiconducting material, such as silicon or germanium, whose electrical conductivity comes only from electron-hole pairs generated by thermal excitation across its own band gap, with no added dopant atoms.
In more detail
At absolute zero, the valence band is completely full and the conduction band empty, so the material behaves as an insulator. As temperature rises, thermal energy promotes some valence electrons across the band gap into the conduction band, leaving an equal number of positively charged holes behind, so electron concentration (n) equals hole concentration (p), both equal to the intrinsic carrier concentration (ni). Because carrier generation depends on temperature, intrinsic semiconductor conductivity increases as temperature rises, unlike a metal's conductivity, which decreases. Adding controlled impurities (doping) converts an intrinsic semiconductor into an n-type or p-type extrinsic semiconductor with much higher, more useful conductivity.
Key facts
| Formula (common example) | Si or Ge |
|---|---|
| Typical band gap | Si: 1.12 eV; Ge: 0.67 eV (at 300 K) |
| Carrier relation | n = p = ni |
| Field | Physical Chemistry |
Ultrapure silicon at room temperature has an intrinsic carrier concentration of about 1.5 x 10^10 carriers per cm^3, giving it very low but measurable conductivity before any doping is introduced.
Frequently asked questions
How does an intrinsic semiconductor differ from an extrinsic semiconductor?
An intrinsic semiconductor is undoped, so its electrons and holes arise only from thermal excitation across the band gap in equal numbers. An extrinsic semiconductor has been deliberately doped with impurity atoms, creating an excess of either electrons (n-type) or holes (p-type) and much higher conductivity.
Why does conductivity increase with temperature in an intrinsic semiconductor?
Higher temperature provides more thermal energy to excite valence electrons across the band gap into the conduction band, creating more electron-hole pairs and thus more charge carriers available to conduct current.