Photoluminescence is the emission of light which is caused by the irradiation of a substance with other light. The term embraces both fluorescence and phosphorescence, which differ in the time after irradiation over which the luminescence occurs. It is used in many photonic devices, for example in light emitting diodes and on phosphor screens.
Photoluminescence is often used in the context of semiconductor devices (e.g. semiconductor lasers and solar cells), even when the luminescent emission is not the actual purpose of the device. Here, photoluminescence is excited by illumination of the device with light which has a photon energy above the band gap energy. The photoluminescence then occurs for wavelengths around the band gap wavelength. The optical spectrum of the photoluminescence (PL spectrum) and also the dependence of its intensity on the irradiation intensity and device temperature can deliver important information for device characterization. In particular, PL spectra and their intensity dependencies can allow one
- to determine the band gap energy and/or the wavelength of maximum gain
- to determine the composition of ternary or quaternary layers
- to determine impurity levels
- to investigate recombination mechanisms
Photoluminescence mappers (PL mappers) can spatially resolve the photoluminescence, e.g. from epitaxially grown wafers. PL maps can reveal, e.g., a radial dependency of layer thickness or material composition.