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
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 r ...
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:
:
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 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