Coupling of geometric confinement and magnetic confinement in In0.09Ga0.91As/GaAs quantum wells in magnetic fields with varying orientations.

Abstract

High excitation photoluminescence investigations of a 30-nm-wide ${\mathrm{In}}_{0.09}$${\mathrm{Ga}}_{0.91}$As/GaAs quantum well have been performed in magnetic fields up to B=10 T with varying orientations and have been compared with the results of detailed numerical calculations. The coupling between the quantum-well confinement potential and the magnetic confinement potential is controlled by the tilt angle \ensuremath{\vartheta} of the magnetic field relative to the quantum-well growth direction. For magnetic fields normal (\ensuremath{\vartheta}=0) and parallel (\ensuremath{\vartheta}=90\ifmmode^\circ\else\textdegree\fi{}) to the quantum-well plane the two confinement potentials are decoupled. In parallel orientation the magnetic quantization enhances only the geometric one. With increasing magnetic field the length scale that determines the quantization changes from the quantum-well width to the magnetic length. In contrast, in a normal magnetic field, B induces, independently of the geometric quantization, the in-plane Landau quantization. Spectral lines arising from intersubband transitions between Landau levels of different quantum-well subbands cross each other when they come close. For all other field orientations the two confinement potentials are coupled. This coupling generates hybridized electronic levels, in which both geometric and magnetic quantization are mixed. Transitions involving levels of different symmetry cross, whereas transitions involving levels of the same symmetry anticross when they approach each other. In addition, the number of strongly allowed transitions is increased near the anticrossing regime due to the exchange of character between the levels.