intrinsic semiconductor
/ in-TRIN-sik SEM-ee-kun-DUK-ter /
Take a perfectly clean crystal of silicon — nothing added, no contaminants, every atom locked snugly to its neighbors. At very low temperature it barely conducts electricity at all, because every electron is busy holding the crystal together and none are free to wander. It sits quietly between a metal, which conducts easily, and an insulator, which hardly conducts at all.
An intrinsic semiconductor is exactly this: a pure material whose only mobile charges come from heat. Warming the crystal shakes a few electrons loose from their bonds, and each escapee leaves behind an empty spot, a hole, that also behaves like a moving charge. So the electrons and holes are always created in equal numbers, in matched pairs. The higher the temperature, the more pairs break free, and the better the crystal conducts.
This matters because intrinsic silicon is the honest starting point — the blank canvas before engineers deliberately add impurities to control it. The common misconception is that 'semiconductor' means a material that conducts moderately well on its own. In truth, pure intrinsic material is a rather poor conductor; nearly all useful behavior in real chips comes from adding tiny, carefully chosen impurities, a step called doping.
Pure silicon at room temperature has only about one mobile electron-hole pair for every ten trillion atoms — so few that the crystal is almost insulating. Heat it gently and its conductivity climbs fast, the opposite of what happens to a metal, where heating makes conduction worse.
In intrinsic silicon, heat — not impurities — is the only source of charge carriers.
Because electrons and holes are born in equal numbers, an intrinsic semiconductor is electrically neutral and behaves the same toward both kinds of carrier — the asymmetry that makes devices useful only appears once you dope it.