Spectroscopic ellipsometry and band structure of Si(sub 1(minus)y)C(sub y) alloys grown pseudomorphically on Si (001)

摘要

The authors have measured the dielectric functions of three Si(sub 1(minus)y)C(sub y) alloys layers (y (le) 1.4%) grown pseudomorphically on Si (001) substrates using molecular beam epitaxy at low temperatures. From the numerical derivatives of the measured spectra, they determine the critical point energies E(sub 0)(prime) and E(sub 1) as a function of y (y (le) 1.4%) using a comparison with analytical line shapes and analyze these energies in terms of the expected shifts and splittings due to negative hydrostatic pressure, shear stress, and alloying. Their data agree well with the calculated shifts for E(sub 1), but the E(sub 0)(prime) energies are lower than expected. They discuss their results in comparison with recent tight-binding molecular dynamics simulations by Demkov and Sankey predicting a total breakdown of the virtual-crystal approximation for such alloys.