Binding energy of excitons to neutral donors inIn0.1Ga0.9As/GaAs quantum wells

The well-width dependence of the binding energy (${\mathit{E}}_{\mathrm{BE}}$) of excitons to neutral donors in high-quality, narrow, pseudomorphic ${\mathrm{In}}_{0.1}$ ${\mathrm{Ga}}_{0.9}$As/GaAs single-quantum-well structures was obtained via low-temperature photoluminescence measurements. It is observed that ${\mathit{E}}_{\mathrm{BE}}$ varies smoothly with well widths for wells that vary from two monolayers (5.7 Å) to ten monolayers (28.5 Å) in width. The results are understood on the basis of simple physical arguments. Additionally, a previously unobserved transition was found for both undoped and donor-doped, two-monolayer-wide ${\mathrm{In}}_{0.1}$ ${\mathrm{Ga}}_{0.9}$As/GaAs quantum wells. This transition is identified with a bound-to-bound transition and is shown to have a significantly faster time-resolved photoluminescence response than those of both the heavy-hole–free-excitonic and neutral-donor–bound-excitonic transitions.