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Electrical and optical pumping

Laser diodes form a subset of the larger classification of semiconductor p – n junction diodes. Forward electrical bias across the laser diode causes the two species of charge carrier – holes and electrons – to be injected from opposite sides of the PIN junction into the depletion region. Holes are injected from the p -doped into the undoped (i) semiconductor, and electrons vice versa. (A depletion region, devoid of any charge carriers, forms as a result of the difference in electrical potential between n - and p -type semiconductors wherever they are in physical contact.) Due to the use of charge injection in powering most diode lasers, this class of lasers is sometimes termed injection lasers, or injection laser diodes (ILD). As diode lasers are semiconductor devices, they may also be classified as semiconductor lasers. Either designation distinguishes diode lasers from solid-state lasers.