CHARACTERIZATION OF VERY THIN GE EPILAYERS ON (100) SI BY SPECTROSCOPIC ELLIPSOMETRY

A series of very thin Ge epilayers (1 - 12 monolayers) grown on Si (100) that had previously been characterized by transmission electron microscopy, X-ray reflection, Rutherford back-scattering, secondary-ion mass spectrometry, Raman spectroscopy and extended X-ray absorption fine structure analysis has been examined by spectroscopic ellipsometry (SE). It was found that the SE results significantly enhance the other findings. Analysis of the SE measurements was based on the nominal growth conditions rather than the results of the post mortem findings mentioned above. This-analysis was able to provide the thicknesses and compositions of the layers comprising the heterostructures easily and quickly. The findings of the previous characterizations of these samples are compared with the results of the SE measurements. The main result is that not even in the thickest epilayer was there a phase that could be described as pure germanium. Intermingling of the Ge epilayer with the Si cap was substantial in every case. It is concluded that the minimum epilayer thickness that would guarantee at least some pure germanium under these conditions is greater than 12 monolayers.