Strain-induced conduction-band nonparabolicity of GaAs-GaAs1−xPxsuperlattices

We present the first quantitative account of the effect of momentum mixing on the conduction-band nonparabolicity in strained layer superlattices. We consider GaAs-${\mathrm{GaAs}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{P}}_{\mathrm{x}}$ superlattices with periods in the range 33.3 to 67.2 Å and x from 0.4 to 1.0. We find that the effect of strain-induced changes in the superlattice wave functions can double the nonparabolicity of the first conduction state. The nonparabolicity along the growth axis 〈001〉 is dominated by virtual excitations involving both the valence and higher-lying conduction states. This is in sharp contrast with the case of GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As superlattices where the effect of the valence bands is generally negligible. We show that the relative position of the secondary conduction X minima plays a crucial role in determining the magnitude of the conduction-band nonparabolicity.