Photoluminescence up-conversion in ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructures

We propose ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructures as a model system to study the phenomenon of photoluminescence (PL) up-conversion and demonstrate low-temperature up-converted PL (UPL) in these heterostructures. We find that a mechanism to prevent up-converted carriers in the ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ layer from thermalizing back to the GaAs layer is essential for efficient UPL. We also find that neither a type-II band alignment nor existence of long-lived intermediate states is an essential requirement of UPL. The results of time-resolved UPL measurements are interpreted within the current models.