MOMENTUM MIXING ENHANCEMENT OF BAND NON-PARABOLICITY IN GAAS-GA1-XALXAS SUPERLATTICES

We present pseudopotential calculations of the conduction and valence mini-band non-parabolicity in GaAs-Ga//1// minus //xAl//xAs superlattices of period approximately 80 Angstrom with various well widths. We find an order of magnitude difference between the non-parabolicity in structures with very narrow approximately 5 Angstrom and wider approximately 40 Angstrom wells. We relate this effect to the competition between quantum-size effects and zone-folding enhanced momentum mixing involving higher levels of X character. We show that the variation of the non-parabolicity of the electron energy with respect to its wavevector across the small Brillouin zone takes on a complicated form which arises due to the anti-crossing behaviour of the higher conduction and lower valence mini-band states. Our results show that non-linear properties of semiconductor superlattices are a sensitive function of the form and position of the higher lying mini-bands which are normally ignored in simple models.