PIEZO-OPTICAL RESPONSE OF SI1-YCY ALLOYS GROWN PSEUDOMORPHICALLY ON SI(001)

We have measured the dielectric functions of three Si1-yCy alloy layer s (y less than or equal to 1.4%) grown pseudomorphically on Si (001) s ubstrates using molecular beam epitaxy at low temperatures. From the n umerical derivatives of the measured spectra, we determine the critica l point energies E(0)' and E(1) as a function of y (y less than or equ al to 1.4%) using a comparison with analytical line shapes and analyze these energies in terms of the expected shifts and splittings due to negative pressure, shear stress, and alloying. Our data agree well wit h the calculated shifts for E(1), but the E(0)' energies are lower tha n expected.