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 contains ...

, in

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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 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 resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

in high injection 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