Photoluminescence Studies of Single GaAs/A1 0.37 Ga 0.63 As Quantum Wells with Extended Monolayer-Flat Regions

We present low-temperature photoluminescence (PL) and excitation (PLE) spectra for single GaAs/A1o.37Ga0.63As MBE-grown quantum wells for which growth was interrupted at each interface for 2 minutes. The multiple lines observed in PL and PLE are ascribed to free-exciton emission from extended (>300A) monolayer-flat regions of the wells differing in thickness by one monolayer. The individual lines are the sharpest and best-resolved ever reported for narrow wells. The remaining inhomogeneous widths place limits on the range of alloy fluctuations in the barrier material. Systematic differences in the relative intensity of the multiple peaks in PL and PLE spectra point to rapid lateral transfer from narrower to wider regions of the wells. PLE spectra also imply efficient transfer of excitation through the 300A barriers individual wells. Lower-energy bands due to lightly-bound excitons are also observed, including a slight increase in neutral-acceptor incorporation.