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.

• Received 12 July 1990

DOI:https://doi.org/10.1103/PhysRevB.42.9562