Spin dynamics of charged excitons in ultrathin (In,Al)(Sb,As)/AlAs and Al(Sb,As)/AlAs quantum wells with an indirect band gap

Abstract

The charged exciton recombination and their spin dynamics are studied in ultrathin InSb- and AlSb-based quantum wells (QWs) surrounded by an AlAs matrix characterized by an indirect band gap. Strong material intermixing was observed that results in the QWs being composed of a quaternary ${\mathrm{In}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{y}{\mathrm{As}}_{1\ensuremath{-}y}$ or a ternary ${\mathrm{AlSb}}_{y}{\mathrm{As}}_{1\ensuremath{-}y}$ alloy. The band alignment in these QWs is identified as type I for (In,Al)(Sb,As)/AlAs and type II for Al(Sb,As)/AlAs. The magnetic-field-induced circular polarization of the photoluminescence ${P}_{c}$ is studied as function of the field strength. The observed nonmonotonic behavior of the ${P}_{c}$ dynamics at high magnetic fields is provided by the interplay of negative and positive trions, contributing to the emission. To interpret the experiment, we have developed a kinetic equation model which accounts for the dynamics of the trion spin states and the redistribution of trions between these states as a result of spin relaxation. The model is in quantitative agreement with the experiment and allows us to determine trion radiative lifetimes on the order of hundreds of microseconds, holes in the trion spin-relaxation times also in the hundreds of $\ensuremath{\mu}\mathrm{s}$ range, electrons in the trion spin-relaxation times of hundreds of ns, and heavy-hole $g$ factors of about $+3.5$ for the structures studied.