Well-width dependence of photoluminescence excitation spectra in GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells

Photoluminescence excitation spectra of high-quality GaAs-${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As quantum wells with various widths have been measured at 77 K. It has been found that the luminescent intensity for excitation photon energies exceeding the barrier band-gap energy exhibits an oscillatory behavior against the well width. The results clearly show that the trapping efficiency of the excited electrons into a well strongly depends on the well width through the resonance and off resonance of the quantum-well levels with the conduction-band bottom of the barrier.