Exciton binding energies from an envelope-function analysis of data on narrow quantum wells of integral monolayer widths inAl0.4Ga0.6As/GaAs

Abstract

Heavy- and light-hole exciton transitions were observed from isolated quantum wells in two wafers of ${\mathrm{Al}}_{0.4}$ ${\mathrm{Ga}}_{0.6}$As/GaAs produced by molecular-beam epitaxy using interrupted growth at the heterointerfaces. The transitions can be assigned to well widths that are integral multiples of a GaAs monolayer width with the integers between 6 and 25. Direct measurements of the barrier-layer band gap and barrier-layer exciton binding energy were also made. A detailed envelope-function analysis of this unique data set revealed the necessity of using a soft-edge potential well rather than a square well when analyzing such narrow wells. A reduction in exciton binding energies of 2.5 meV from free charge arising from unintentional barrier doping of ∼1×${10}^{14}$ ${\mathrm{cm}}^{\mathrm{-}3}$ was found. Exciton binding energies for wells between 17 and 70 Å are deduced from the analysis.