What makes a dopant a donor or an acceptor?

A donor has one more valence electron than the host atom it replaces, easily giving it up to the conduction band (n-type); an acceptor has one fewer, capturing an electron from the valence band and leaving a hole (p-type).

Why does an intrinsic semiconductor conduct better when heated?

Raising the temperature gives more electrons enough energy to cross the band gap, exponentially increasing the number of electron-hole pairs available to carry current, the opposite of a metal whose conductivity falls with heating.

Intrinsic and Extrinsic Semiconductors

A pure semiconductor conducts only through thermally generated electron-hole pairs, but deliberately adding donor or acceptor impurities transforms it into n-type or p-type material with controllable conductivity.

Najít téma v PaperMindJiž brzyFind papers & topics

Tools & resources

Stáhnout prezentaci

Learn & explore

VideoJiž brzy

Definition

An intrinsic semiconductor is a pure crystal in which equal numbers of electrons and holes are generated by thermal excitation across the band gap; an extrinsic semiconductor is one doped with donor or acceptor impurities that create an excess of one carrier type, making it n-type or p-type.

Scope

This topic distinguishes intrinsic semiconductors, where electron and hole concentrations are equal and set by thermal excitation across the gap, from extrinsic (doped) semiconductors, where donor or acceptor impurities supply majority carriers. It covers the shallow donor and acceptor levels, ionization, the freeze-out, extrinsic, and intrinsic temperature regimes, and the resulting temperature dependence of carrier concentration. It sets up the carrier-statistics and junction topics that follow.

Core questions

How are carriers created in a pure semiconductor, and why does the intrinsic concentration rise steeply with temperature?
How do donor and acceptor impurities produce n-type and p-type material?
Why are dopant energy levels shallow, and how does ionization vary with temperature?
What are the freeze-out, extrinsic, and intrinsic regimes of carrier concentration?

Key concepts

Intrinsic carrier concentration
Donor and acceptor impurities
n-type and p-type material
Shallow impurity levels and ionization
Freeze-out, extrinsic, and intrinsic regimes

Clinical relevance

The controlled doping that distinguishes extrinsic from intrinsic material is the basis of all semiconductor devices; selecting dopant type and concentration sets the carrier density and conductivity of the regions that form diodes, transistors, and integrated circuits.

History

The role of impurities in semiconductor conduction was clarified in the 1930s and 1940s, and the development of controlled doping and single-crystal growth at Bell Labs in the late 1940s and early 1950s made reproducible n-type and p-type material possible, enabling the transistor and the semiconductor industry.

Key figures

William Shockley
Gordon Teal
Walter Brattain

Seminal works

sze2007
ashcroft1976

Frequently asked questions

What makes a dopant a donor or an acceptor?: A donor has one more valence electron than the host atom it replaces, easily giving it up to the conduction band (n-type); an acceptor has one fewer, capturing an electron from the valence band and leaving a hole (p-type).
Why does an intrinsic semiconductor conduct better when heated?: Raising the temperature gives more electrons enough energy to cross the band gap, exponentially increasing the number of electron-hole pairs available to carry current, the opposite of a metal whose conductivity falls with heating.