A detailed study of reduced-basis tight-binding models of electrons in semiconducting quantum wells is presented. The focus is on systems with degenerate valleys, such as silicon in silicon germanium heterostructures, in the low-density limit, relevant to proposed quantum computing architectures. Analytic results for the bound states of systems with hard-wall boundaries are presented and used to characterize the valley splitting in silicon quantum wells. The analytic solution in a no-spin-orbit model agrees well with larger tight-binding calculations that do include spin-orbit coupling. Numerical investigations of the valley splitting for finite band offsets are presented that indicate that the hard-wall results are a good guide to the behavior in real quantum wells.

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