Optimization of the confinement energy of quantum-wire states in T-shaped GaAs/Al xGa 12xAs structures

We report on an optimization of the wire confinement energies of the confined electronic states at the
T-shaped intersection of GaAs and Al xGa 12xAs quantum wells. These structures can be produced by the
cleaved edge overgrowth technique. We present an analytical model for the confinement to give insight into the
basic mechanism. The optimization of the confinement energy is done by calculations in a six-band k•p
approximation for the valence band and in an isotropic effective-mass approximation for the conduction band.
The confined valence-band states are only weakly bound at the T-shaped intersection due to the large and
anisotropic hole effective masses. Employing optimized sample parameters, confinement energies for the
free-electron-hole pairs are nearly doubled compared to symmetric structures, and 34 meV are predicted for a
3-nm overgrown GaAs well. This is expected to be further enhanced by the Coulomb interaction, that is
neglected in the numerical model. The experimental structures grown using the optimized geometry show wire
confinement energies of up to 54 meV, which is significantly larger than KT at room temperature and larger
than previously reported.