Reflectance Difference Spectroscopy (RDS) is a powerful tool for the optical characterization of cubic semiconductors.
Several physical mechanisms have been identified to contribute to the RDS signal. Among these we can count on
surface electric fields, lineal defects, and surface strains. The RDS setups reported so far, use photodiodes and
photomultipliers as light detectors and lock-in techniques to process the signal. In the present work we describe a new
instrument based on a charged-coupled device (CCD) as light detector. By focusing the light on the CCD, it is possible
to obtain the RD spectra coming from different regions of the semiconductor surface, by analyzing the spectra for a
group of pixels of the CCD. The instrument can be used to obtain a topographic map of the surface of the semiconductor.
We report on in situ Reflectance Difference Spectroscopy measurements carried out on GaAs (001). Measurements were
performed at temperatures of 580 °C and 430 °C, in both n and p-type doped films and for both (2x4) and c(4x4)
reconstructions. Samples employed were grown by Molecular Beam Epitaxy with doping levels in the range from
1016 - 1019 cm-3. We demonstrate the potential of Reflectance Difference Spectroscopy for impurity level determinations under growth conditions.
We report on the application of reflectance-difference (RD) spectroscopy to the characterization of 60 degree dislocations in zincblend semiconductors. We discuss a physical model based on dislocation induced anisotropic strains which predict a RD lineshape proportional to the first energy derivative of the semiconductor reflectance spectrum. We present RD spectra for semi-insulating GaAs:Cr (100) crystals in the 1.2 - 3.5 eV energy range, which show a first derivative component in accordance to our model. From a fitting of the experimental RD spectra to the theoretical lineshape we obtain average values for the strains associated to 60 degree dislocations. We also show that for the samples reported in this paper the dislocation-induced anisotropic strain results in a normalized effective change in lattice constant in the range from 10-5 to 10-4.