Hole effective masses in relaxed Si12xCx and Si12yGey alloys

We report hole effective mass calculations of Si12xCx and Si12yGey alloys. All calculations are based on a 16316 Hamiltonian matrix constructed from the linear combination of atomic orbital approximation with spin-orbit interaction taken into consideration. The 1 meV constant energy surfaces below the valence band edge are used to determine the nominal hole effective masses. The effective masses of light hole and heavy hole of Si12yGey alloys vary as linear functions of Ge content and increase linearly as the hole energy increases from 1 to 15 meV. The heavy hole effective masses of Si12xCx alloys, however, exhibit a totally different trend. The effective mass of Si12xCx remains relatively unchanged from x50.0 to x50.9, and increases abruptly by a factor of two from x50.9 to x51.0. The nonparabolicity increases as the C content rises up to x50.9, and nearly disappears when turning into pure diamond. The interaction between the split-off hole band and the heavy hole band is proposed for the anomalous behavior of the heavy hole effective masses of SiC alloys. © 1997 American Institute of Physics. @S0003-6951~97!02911-2#