Low-level injection conditions for a
p–n junction, in
physics
Physics is the scientific study of matter, its Elementary particle, 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 whi ...
and
electronics
Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...
, 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:
:
where
is the number of electrons,
is the excess carriers injected into the semiconductor, and
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:
:
The assumption of low-level injection can be made regarding an n-type semiconductor, which affects the equations in the following way:
:
Therefore
and
.
In comparison, a
semiconductor
A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...
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
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Semiconductors