Introduction to Semiconductors

These vocabulary flashcards cover the fundamental concepts of semiconductors, including atomic structure, material classification (conductors, insulators, semiconductors), energy bands, doping types (N-type and P-type), and the functional characteristics of PN junction diodes.

Atoms

The smallest particle of an element that retains the characteristic of that element.

Protons

Positive charged particles located in the nucleus.

Electron

Negatively charged particles that revolve around the nucleus in a fixed orbit.

Neutrons

Uncharged particles that, along with protons, form the nucleus.

Valence electrons

Electrons that are in orbits farther from the nucleus, have higher energy, and are less tightly bound to the atom than those closer to the nucleus.

Ionization

The process of losing a valence electron; when a free electron loses energy and falls into the outer shell of a neutral atom, the atom becomes a negative ion.

Valence shell

The outer most shell of an atom.

Atomic Number

Equals the number of protons in the nucleus, which is the same as the number of electrons in an electrically balanced (neutral) atom.

Free Electron

The escaped valence electron, also called a conduction electron.

Insulator

A material that does not conduct electrical current under normal conditions, with valence electrons tightly bound to the atoms (e.g., rubber, plastics, glass).

Conductor

A material that easily conducts electric current, containing many free electrons (e.g., copper, silver, gold, and aluminum).

Semiconductor

A material that is between conductors and insulators in its ability to conduct electrical current, typically having $4$ valence electrons (e.g., silicon, germanium, and carbon).

Intrinsic Silicon

A pure silicon crystal at room temperature.

Hole

A vacancy left in the valence band within the crystal when an electron jumps to the conduction band.

Recombination

Occurs when a conduction-band electron loses energy and falls back into a hole in the valence band.

Energy Gap

The difference in energy between the valence band and the conduction band.

Covalent bond

A bond created when a center silicon atom shares an electron with each of the four surrounding silicon atoms.

Electron current

A type of current in a semiconductive material caused by the movement of free electrons in the conduction band.

Hole current

A current that moves into a nearby hole with little change in energy level, leaving another hole where it came from; it occurs in the opposite direction of electron movement.

Doping

A process of increasing the number of current carriers by adding impurities to the intrinsic semiconductive material.

N-type Semiconductor

A semiconductor created by adding pentavalent impurity atoms to increase the number of conduction-band electrons in intrinsic silicon.

Donor atom

A pentavalent impurity atom with five valence electrons, such as arsenic, phosphorus, bismuth, or antimony, that gives up an electron.

P-type Semiconductor

A semiconductor created by adding trivalent impurity atoms to increase the number of holes in intrinsic silicon.

Acceptor atom

A trivalent atom that can take an electron, such as boron.

Diode

A device that conducts current in only one direction.

PN Junction

The boundary between the regions of n-type and p-type materials.

Depletion Region

A region near the pn junction where charge carriers (holes and electrons) are depleted due to diffusion across the junction.

Barrier Potential

The potential difference of the electric field across the depletion region, representing the voltage required to move electrons through the electric field.

Silicon Barrier Potential

$0.7\,V$ at $25$ degrees Celsius.

Germanium Barrier Potential

$0.3\,V$ at $25$ degrees Celsius.

Bias

The use of a dc voltage to establish certain operating conditions for an electronic device.

Forward Bias

The condition that allows current through the pn junction.

Reverse Bias

The condition that essentially prevents current through the diode.

Dynamic resistance

The internal resistance of the material, which is very small and usually neglected.

Reverse current

The extremely small current that exists in the reverse bias after the transition current disappears.