Optical anisotropy of organic layers on GaAs(001)

The application of the linear-optical, polarization sensitive methods, in s itu reflectance anisotropy spectroscopy (RAS), and ex situ spectroscopic el lipsometry, for the characterization of organic layers is discussed and the results of the investigation of 3,4,9,10-perylenetetracarboxylic dianhydri de (PTCDA) layers on sulfur passivated GaAs(001) surfaces are presented. Th e organic layers were grown via organic molecular beam deposition at room t emperature. The RA spectrum of the sulfur terminated GaAs surface shows a d erivative like feature at E-1 gap and a feature in the higher energy range related to E-2 of bulk GaAs. Upon the PTCDA deposition, additional features appear in the spectra which can be attributed to PTCDA while the GaAs feat ure near El remains unchanged indicating that the surface reconstruction st ays intact. The imaginary part of the pseudo-dielectric function is found t o be angular dependent. This dependence also changes as a function of azimu thal angle. While the first can be well described using existing models for optical uniaxial layers, the latter is likely to be related to in-plane op tical anisotropy. (C) 2001 American Vacuum Society.