A He-Ne laser or monochromatic light from monochromator 2 pumps an area of the sample. The pump beam is modulated by a chopper. A monochromator 1 selects a spectral bandpass of light from the source. This illumination beam is imaged onto the sample and after reflection focused on the photodiode. The detected signal is processed via a lock-in amplifier that is referenced to the chopper frequency. Setups are equipped with x-y motion stages which allows to achieve photoreflectance maps.
Spatially-resolved photoreflectance
Standard PR set-up
Enhanced PR set-up
Photoreflectance spatially resolved map of AlGaAs/GaAs/InGaAs QW based laser structure
High resolution photoreflectance map of undoped structure. Spectral region covers the quantum well resonance. The change in wavelength distribution over the scanned area is visible. On the right hand side of the figure an example of PR spectrum is shown.