Low-level injection

The following equation must be satisfied for a semiconductor under carrier injection conditions:

${\displaystyle n=\Delta n+n_{0},}$

where ${\displaystyle n}$ is the number of electrons, ${\displaystyle \Delta n}$ is the excess carriers injected into the semiconductor, and ${\displaystyle n_{0}}$ 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:

${\displaystyle \Delta n=\Delta p.}$

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

${\displaystyle \Delta n\ll N_{D}.}$

Therefore ${\displaystyle n=N_{D}}$ and ${\displaystyle p=\Delta p+p_{0}}$.