Energy band structure of Bi-Bi_1-xSb_xcompositional superlattices

Abstract

Within the McClure model a dispersion equation for the energy spectrum of the Bi-Bi1-xSbx superlattices in the envelope function approximation is derived. The effective mass of minibands, the Fermi energy and the concentration of free carriers in a superlattice with X=0.1 and the period d=10 nm are determined. The dependence of the miniband energy upon the ratio r=dI/dII is obtained (dI is the thickness of the Bi layers and dII 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 the L and T points of the Brillouin zone. For dI=4 nm and dII=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. In the superlattice with X=0.12 and dI=dII=60 nm the transverse components of the effective-mass tensor change signs at a certain value of q=qo. 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'.

Effect of energy level matching on the enhancement of photovoltaic response about oxide/Zn2SnO4 composites

“…7(b). [64][65][66][67][68][69][70][71] So these phenomena will promote the transfer of photogenerated charges. It is inferred that a smaller difference in the conduction band edges and a larger overlapping of the wave functions will facilitate the photogenerated charges migration and separation, which will induce a higher efficiency of photovoltaic conversion.…”