Tight-binding analysis of energy-band structures in quantum wires

The tight-binding method is applied to the analysis of the energy bands of GaAs-${\mathrm{Al}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ga}}_{\mathit{x}}$As quantum wires parallel to the [110] orientation. The results indicate that the effective mass of electrons parallel to the quantum wires in the lowest conduction band in a typical case studied can be as much as 50% larger than that of bulk GaAs and that in the second-lowest conduction band even larger. In the valence band, the reduced symmetry of the quantum wire causes enhanced heavy-hole–light-hole mixing and therefore increased nonparabolicities and reduced effective masses of the uppermost valence band. In a case studied this mass was reduced by a factor of 0.65 compared with a similarly dimensioned quantum well. The negative-effective-mass properties of the lower valence subbands are also increased relative to quantum wells. These changes in the energy-band structure would significantly affect mobilities, the transitions between subbands, and lasing characteristics of quantum-wire devices.