Effective-mass enhancement and nonparabolicity in thin GaAs quantum wells

We study size quantization effects on the conduction band dispersion in GaAs/AlAs quantum wells using a semiempirical tight-binding method. For GaAs well thicknesses between 3 and 11 nm, we find a significant increase of the conduction band mass of up to 50% compared with bulk GaAs. Concomitantly, the confinement reduces the highest achievable group velocities for electrons in the Γ conduction valley of the well by up to 30%. We discuss some of the consequences for quantum-well-based devices.