Piezo-optical response of Si_1-yC_y alloys grown pseudomorphically on Si (001)

We have measured the dielectric functions of three Si1-yCy alloy layers (y ≤ 1.4%) grown pseudomorphically on Si (001) substrates using molecular beam epitaxy at low temperatures. From the numerical derivatives of the measured spectra, we determine the critical point energies E′0 and E1 as a function of y (y ≤ 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 with the calculated shifts for E1, but the E′0 energies are lower than expected. © 1995.