Applicability of the six-band kp -model equations to semiconductor heterostructures

The problem of the applicability of the six-band kp -model to heterostructures with sharp boundaries is studied by calculating the energy spectrum of holes in the Ge/Si system with quantum dots. The boundary conditions which satisfy the conditions of particle flux conservation and the wave function continuity on the heterojunction are formulated at the level of differential equations and are characterized by a single parameter µ, which depends on the heterojunction properties. It is shown that a certain choice of µ leads to nonphysical interface states that fill the entire band gap. Conditions (range of µ) for the absence of such nonphysical states are determined by considering the simplest cases —a single heterojunction and a quantum well..