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.
Photoluminescence is often used in the context of semiconductor devices (e.g. semiconductor lasers or amplifiers, solar cells, or saturable absorbers). Here, photoluminescence is excited by illumination of the device with light which has a photon energy above the bandgap energy. The photoluminescence then occurs for wavelengths around the bandgap 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 bandgap 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.
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