Carrier repopulation process for spatially-ordered InAs/InAlGaAs quantum dots

From the transmission electron microscope image, the seven-stacked InAs/InAlGaAs QDs on an InP substrate were spatially ordered instead of usual on-top vertical alignment. The increasing rate of the QD size became almost saturated by increasing the number of layers. The photoluminescence (PL) intensity for the seven-stacked InAs/InAlGaAs QDs was decreased up to 60K and remained almost stable at the temperature range from 60 to 220K. And then, the intensity was again drastically decreased with further increasing temperature. The emission peak was first red-shifted at the ratio of 0.446 meV/K from 20 to 60K. However, the degree of the red-shift in the emission peak from 60 to 220K was decreased at the negligibly small ratio of 0.028 meV/K. Above 220K, the emission peak was again significantly decreased at the ratio of 0.323 meV/K. While increasing the temperature, the carrier lifetimes obtained from the PL decay profiles for the seven-stacked QDs initially enhanced and then, almost stable at a certain temperature range. Finally, the PL decay time was decreased with further increasing temperature. These behaviors can be explained by the partial repopulation process of thermally excited carriers among QDs.