Theory of the hole subband dispersion in strained and unstrained quantum wells

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Abstract
We use the spherical model to derive simple selection rules for the mixing and dispersion of light- and heavy-hole subbands in both strained and unstrained quantum-well systems. The valence-subband structure of such systems can display surprising features with, for instance, the highest hole band being light-hole-like in the well plane near the zone center and strongly nonparabolic at larger wave vectors. We use the infinite square-well potential to show how these and other unintuitive features in the valence-subband dispersion can be understood in terms of interactions between the two highest heavy-hole subbands and the highest light-hole subband. Finally, we give guidelines for optimizing the valence-subband structure for specific applications: first to achieve maximal light-hole behavior and second for a highly nonparabolic band structure for nonlinear devices.