The optical absorption of hetero-epitaxial layers which had been grown onto exactly [001]-oriented Si substrates was investigated by means of spectroscopic ellipsometry, combined with anodic stripping. At wavelengths which were above the bandgap-equivalent wavelength, considerable absorption was found which depended upon the dislocation density in the layer. A theoretical model that was based upon the electric micro-fields of charged dislocations was developed, and the predictions agreed closely with experimental results. Differential spectroscopic ellipsometry was then used to determine the dislocation-density profiles in the InP and GaAs layers. The dislocation density could be determined within a few tens of nm from the hetero-interface of InP on Si. The identification and counting of dislocations was not possible by using other methods.

H.Iber, E.Peiner, A.Schlachetzki: Journal of Applied Physics, 1996, 79[12], 9273-7