Optoelectronics

At a p-n junction made of a direct-bandgap semiconductor, injected electrons and holes recombine and emit a photon. The light's wavelength is set by the material system's bandgap (e.g., InGaN for blue, AlGaInP for red). Quantum well structures in the active region significantly boost the efficiency of this recombination.

Learn more in the chapter Light-Emitting Diodes (LED) →

As with an LED, light is generated by recombination at a p-n junction, but here inside an optical resonator that reflects the light back and forth repeatedly. Above a threshold current, stimulated emission dominates over spontaneous emission — population inversion occurs and coherent laser light is produced. Depending on the resonator design, this yields Fabry-Pérot, DFB, or VCSEL lasers, among others.

Learn more in the chapter Laser Diodes →