Phenomenon
Low-level injection conditions for a p–n junction, in physics and electronics, 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:
formula_1
where formula_2 is the number of electrons, formula_3 is the excess carriers injected into the semiconductor, and formula_4 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:
formula_5
The assumption of low-level injection can be made regarding an n-type semiconductor, which affects the equations in the following way:
formula_6 
Therefore formula_7 and formula_8.
In comparison, a semiconductor 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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