Low-level injection conditions for a

p–n junction A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contai ...

, in

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which rel ...

and

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

, refers to the state where the number of

minority carriers In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used ...

generated is small compared to the majority carriers of the material. The semiconductor's majority-carrier concentration will remain (relatively) unchanged, while the minority-carrier concentration sees a large increase. In this condition minority-carrier recombination rates are linear. The following equation must be satisfied for a semiconductor under carrier injection conditions: :

n = \Delta n + n_0,

where

n

is the number of electrons,

\Delta n

is the excess carriers injected into the semiconductor, and

n_0

is the equilibrium concentration of electrons in the semiconductor The following relation must also be true, because for every electron injected a hole must also be created to keep a balance of charge: :

\Delta n = \Delta p.

The assumption of low-level injection can be made regarding an n-type semiconductor, which affects the equations in the following way: :

\Delta n \ll N_D.

Therefore

n = N_D

and

p = \Delta p + p_0

. In comparison, a

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

high injection High may refer to: Science and technology * Height * High (atmospheric), a high-pressure area * High (computability), a quality of a Turing degree, in computability theory * High (tectonics), in geology an area where relative tectonic uplift to ...

means that the number of generated carriers is large compared to the background doping density of the material. In this condition minority carrier recombination rates are proportional to the number of carriers squared.

References

{{Reflist Semiconductors