ENERGY-BAND STRUCTURE OF BI-BI1-XSBX COMPOSITIONAL SUPERLATTICES

Within the McClure model a dispersion equation for the energy spectrum of the Bi-Bi1-xSbx superlattices in the envelope function approximati on is derived. The effective mass of minibands, the Fermi energy and t he concentration of free carriers in a superlattice with X = 0.1 and t he period d = 10 nm are determined. The dependence of the miniband ene rgy upon the ratio r = d(I)/d(II) is obtained (d(I) is the thickness o f the Bi layers and d(II) is the thickness of the alloy layers). It is shown that there is a transition from the semiconducting state (r < 0 .31) to the semimetallic state (r > 0.31) in the superlattice with X = 0.1 and d = 10 nm due to an energy overlap between the minibands at t he L and T points of the Brillouin zone. For d(I) = 4 nm and d(II) = 6 nm the Fermi surface of electrons is closed whereas the Fermi surface of holes is open in the direction of the superlattice wavevector q. I n the superlattice with X = 0.12 and d(I) = d(II) = 60 nm the transver se components of the effective-mass tensor change signs at a certain v alue of q = q0. As a result, at q > q0 the dependence of the miniband energy on the wavevector k in the plane of layers has a shape like a ' camel's back'.