Photoreflectance and contactless electroreflectance measurements of semiconductor structures by using bright and dark...

Experimental setup for measurements of photoreflectance (PR) and contactless electroreflectance (CER) spectra in bright and dark configurations is described in this work and applied to study various semiconductor structures. The innovative solution in this setup is the possibility to measure PR and CER spectra in both experimental configurations with the same halogen lamp, monochromator, detector, and only very small modification in the optical path. In this setup the measurement conditions for the two experimental configurations are very similar, and the obtained PR and CER spectra can be compared and discussed in the context of the unwanted constant photovoltaic (PV) effect, which appears in the bright configuration when the sample is illuminated by the spectrum of white light instead of the monochromatic light. It has been clearly shown that for (i) epitaxial layers, (ii) quantum wells, and (iii) quantum dots, exactly the same spectral features are observed in both configurations at room temperature. It means that from the viewpoint of the detection of optical transitions, it is not important what configuration is used since the white light-induced PV effect does not influence the energy of optical transitions in these structures.