Electronic subbands for Al_xGa_1-xAs/GaAs multilayer and superlattice structures

We have carried out calculations of the conduction bandstructure for GaAs/Al_xGa_1-xAs (0<x≤1) multilayer structures with very thin layers. We report results for the case of a small number of layers for which the quasi-continuous bandstructure of a large superlattice is a poor approximation. Using a multivalley effective mass approach which includes nonparabolicity, we find that for large aluminum concentrations and thin layers the lowest bound state is derived from the X valley and is localized mainly in the alloy layers. The structures investigated have a range of design parameters which is useful for superlattice modulation-doped field-effect transistors.