Semiconductor light sources

Two types of electroluminescent diode are discussed with a view to their applications in optical telecommunications. Light-emitting diodes (LEDs) produce incoherent radiation, while laser diodes (injection or junction lasers) are coherent emitters. A basic review is made of the physics of semiconductor light emission, including semiconductor materials and threshold emission conditions. The similarities and differences of the two types of semiconductor emitter are indicated. The electrical input characteristics, the optical output (including radiance, directivity, and spectrum), and the transfer characteristics (quantum efficiency and response curve) are compared. The effects of degradations on the lifetime and reliability of electroluminescent emitters are discussed.