Heavy-light hole mixing at zinc-blende (001) interfaces under normal incidence

The reduced point symmetry C-2v of a zinc-blende-based (001) interface allows mixing between heavy- and light-hole states even under normal incidence. We have generalized the envelope function approximation to take into account such a mixing by including off-diagonal terms into boundary conditions for the envelopes. The normal off-diagonal hole reflection from a GaAs/AlAs(001) heterointerface as well as Gamma-point interband matrix elements in GaAs/AlAs multilayered structures have been calculated and the results have been compared with those obtained by pseudopotential and tight-binding calculations. The best fit with the numerical calculations gives for the dimensionless heavy-light hole mixing coefficient values t(l-h)=0.9 and 0.32. The theory of exchange splitting of excitonic levels in type II GaAs/AlAs superlattices has been extended to include not only the heavy-light hole mixing but also an admixture of spin-orbit-split states in the heavy-hole wave function. An agreement between theory and experiment for the anisotropic exchange splitting has been achieved for t(l-h)=0.5 A tight-binding model has been used to relate the microscopic parameters with coefficients in the boundary conditions for the hole envelope function. The tight-binding model estimation of t(l-h)=0.44 is in reasonable agreement with the other estimations of t(l-h).