Altering the Optical Properties of GaAsSb-Capped InAs Quantum Dots by Means of InAlAs Interlayers

In this work, we investigate the optical properties of InAs quantum dots (QDs) capped with composite In_0.15Al_0.85As/GaAs_0.85Sb_0.15 strain-reducing layers (SRLs) by means of high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) spectroscopy at 77 K. Thin In_0.15Al_0.85As layers with thickness t = 20 Å, 40 Å, and 60 Å were inserted between the QDs and a 60-Å-thick GaAs_0.85Sb_0.15 layer. The type II emissions observed for GaAs_0.85Sb_0.15-capped InAs QDs were suppressed by the insertion of the In_0.15Al_0.85As interlayer. Moreover, the emission wavelength was blueshifted for t = 20 Å and redshifted for t ≥ 40 Å resulting from the increased confinement potential and increased strain, respectively. The ground state and excited state energy separation is increased reaching 106 meV for t = 60 Å compared to 64 meV for the QDs capped with only GaAsSb SRL. In addition, the use of the In_0.15Al_0.85As layers narrows significantly the QD spectral linewidth from 52 to 35 meV for the samples with 40- and 60-Å-thick In_0.15Al_0.85As interlayers.