Direct coupling of heavy-hole free excitons in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells with free excitons in the GaAs barrier

Enhanced emission due to heavy-hole free-exciton (HHFE) collapse in narrow (${\mathit{L}}_{\mathit{z}}$≤50 Å single ${\mathrm{In}}_{0.1}$ ${\mathrm{Ga}}_{0.9}$As/GaAs quantum wells was observed when the excitation energy was resonant with the GaAs-barrier free-exciton energy. The observed resonant excitation behavior along with the marked difference in the effect of an applied magnetic field on the HHFE emission strength for the cases of nonresonant and resonant excitation is consistent with a model of direct coupling between the GaAs-barrier free-exciton level and the ${\mathrm{In}}_{0.1}$ ${\mathrm{Ga}}_{0.9}$As-quantum-well heavy-hole free-exciton level. The direct coupling between the GaAs-barrier free-exciton level and the quantum-well HHFE level is a result of wave-function overlap accomplished by extension of the HHFE wave function into the barrier region. As a result of this direct coupling, when several ${\mathrm{In}}_{0.1}$ ${\mathrm{Ga}}_{0.9}$As quantum wells of different sizes are present in the same sample, excitation at the GaAs-barrier free-exciton formation energy simultaneously resonantly excites HHFE emission from all of the ${\mathrm{In}}_{0.1}$ ${\mathrm{Ga}}_{0.9}$As wells for the well sizes studied (${\mathit{L}}_{\mathit{z}}$≤50 Å).