Influences of dot-in-a-well structure and GaAs insertion layer on InP-based InAs quantum dots

The structural and optical properties of InAs quantum dots (QDs) embedded in an In 0.85 Ga 0.15 As 0.32 P 0.68 matrix with the emission wavelength of 1.10 µm (1.1Q-InGaAsP) on InP were modified by adopting an In 0.69 Ga 0.31 As 0.67 P 0.33 (1.35 µm, 1.35Q-InGaAsP) quantum-well (QW) structure (dot-in-a-well, DWELL) and by inserting an additional GaAs layer right below the QDs. The spatial QD density with the DWELL structure and the GaAs insertion layer was reduced by 53% from that for the simple InAs QDs with only a 1.1Q-InGaAsP barrier (reference sample). However, the photoluminescence intensity was improved by more than 2.5 times compared to that of the reference sample. These results are discussed in terms of the increase in the capture probability of carriers due to the 1.35Q-InGaAsP QW and the relatively strong localization of carriers according to variations in the wetting layer and the distances among QDs.