Ellipsometry Studies, Optical Properties, And Band Structure of Gel. 1- y C y , Ge-RICH Si 1- x-y Ge x C y , And Boron-Doped Si 1- x Ge x Alloys

We measured the pseudodielectric function (PDF) of Ge 1- y C y and Ge-rich Si 1- x-y Ge x C y alloys from 1.1 to 5.2 eV using spectroscopic ellipsometry. These alloys were grown by molecular beam epitaxy at 6000C on (001) Si substrates. Analytical lineshapes fitted to numerically calculated derivatives of their PDFs determined the critical-point parameters of the E 1 , E 1 +Δ 1 , E 0 ', and E 2 transitions. The critical-point energies of the Ge 1- y C y alloys were found to be similar to bulk Ge. This indicates that the presence of C in these alloys only has a small influence on the band structure. For some samples, the amplitude of the PDF is much lower than in bulk Ge, which can be attributed to surface roughness and explained within the framework of the Kirchhoff theory of diffraction or using effective medium theory. The degree of surface roughness indicated by optical measurements was confirmed by atomic force microscopy. We also studied bulk Czochralski-grown Si 1- x Ge x alloys (0