MIXING OF SUBBANDS IN GAAS/ALAS SUPERLATTICES WITH RANDOMLY DISTRIBUTED LAYER THICKNESSES

The hole subband structure of GaAs/AlAs superlattices with randomly distributed layer thicknesses is studied with the Luttinger-Kohn Hamiltonian in the Wannier-Bloch mixing representation. By use of Dean's method, the eigenvalues and the subband structure of holes are calculated for several samples with various distributions of the random layer thicknesses. From these results, it is seen that the strong mixing of the hole subbands results in large nonparabolicities in the hole subbands. With an increasing degree of randomness, the effect becomes more and more apparent. It is also found that the introduction of the randomness in the layer thicknesses gives rise to a reduction of the energy gaps and the differences between the hole subbands, and an increase of the total widths of the hole minibands. The effect of the mixing on the optical properties is also qualitatively discussed.