Intrinsic, n-type, and p-type Semiconductors

Check whether the semiconductor is pure or doped. If doped, identify dopant valency. Group V means donor impurity and n-type. Group III means acceptor impurity and p-type. State majority and minority carriers clearly.

Show silicon covalent bonds with one pentavalent dopant for n-type and one trivalent dopant for p-type. Label donor atom, acceptor atom, free electron, hole, majority carrier, and minority carrier. The important visual point is that the dopant changes carrier availability, not the basic crystal framework.

Writing that boron-doped silicon has free electrons as majority carriers is wrong because boron is trivalent and produces holes as majority carriers.

An intrinsic semiconductor is a pure semiconductor such as silicon or germanium. An extrinsic semiconductor is formed by adding a small controlled amount of impurity, called a dopant, to increase charge carriers; pentavalent dopants produce n-type material and trivalent dopants produce p-type material.

An intrinsic semiconductor is a pure semiconductor such as silicon or germanium. An extrinsic semiconductor is formed by adding a small controlled amount of impurity, called a dopant, to increase charge carriers; pentavalent dopants produce n-type material and trivalent dopants produce p-type material. Carrier rule: in intrinsic semiconductors, electron concentration equals hole concentration. In n-type material, electrons are majority carriers and holes are minority carriers. In p-type material, holes are majority carriers and electrons are minority carriers. Doping must be small and controlled so the semiconductor lattice is modified without becoming a metal. If a silicon crystal is doped with phosphorus, it becomes n-type because phosphorus has five valence electrons and one electron is loosely available for conduction. If silicon is doped with boron, it becomes p-type because boron has three valence electrons and creates a hole in the bonding structure.

In pure silicon or germanium, each atom forms four covalent bonds, and electron-hole pairs are generated thermally. The number of electrons equals the number of holes in an intrinsic semiconductor. In n-type semiconductors, a group V atom such as phosphorus contributes an extra electron, so electrons become majority carriers. In p-type semiconductors, a group III atom such as boron creates an electron deficiency in bonding, so holes become majority carriers. The doped crystal remains electrically neutral overall; it only has more mobile carriers of one type. Carrier rule: in intrinsic semiconductors, electron concentration equals hole concentration. In n-type material, electrons are majority carriers and holes are minority carriers. In p-type material, holes are majority carriers and electrons are minority carriers. Doping must be small and controlled so the semiconductor lattice is modified without becoming a metal. A germanium sample is doped with arsenic. Arsenic is a group V element, so it has one more valence electron than germanium needs for four covalent bonds. The sample becomes n-type, electrons are majority carriers, holes are minority carriers, and arsenic acts as a donor impurity. Questions often ask for differences between intrinsic and extrinsic semiconductors, identification of n-type or p-type from dopant valency, or correction of the misconception that doped semiconductors carry net charge. Writing that boron-doped silicon has free electrons as majority carriers is wrong because boron is trivalent and produces holes as majority carriers.