Optimization of the confinement energy of quantum-wire states in T-shaped GaAs/AlxGa1-xAs structures.

Abstract

We report on an optimization of the wire confinement energies of the confined electronic states at the T-shaped intersection of GaAs and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As 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\ensuremath{\cdot}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. \textcopyright{} 1996 The American Physical Society.