Inhibited carrier transfer in ensembles of isolated quantum dots

We report significant differences in the temperature-dependent and time-resolved photoluminescence (PL) from low and high surface density ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}/\mathrm{GaAs}$ quantum dots (QD’s). QD’s in high densities are found to exhibit an Arrhenius dependence of the PL intensity, while low-density (isolated) QD’s display more complex temperature-dependent behavior. The PL temperature dependence of high density QD samples is attributed to carrier thermal emission and recapture into neighboring QD’s. Conversely, in low density QD samples, thermal transfer of carriers between neighboring QD’s plays no significant role in the PL temperature dependence. The efficiency of carrier transfer into isolated dots is found to be limited by the rate of carrier transport in the ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ wetting layer. These interpretations are consistent with time-resolved PL measurements of carrier transfer times in low and high density QD’s.