Effect of spacer layer thickness on the optical properties of stacked InAs/InAlAs quantum wires grown on InP (001)

Stacked structures containing InAs quantum wires (QWRs) have been successfully grown on In0.52Al0.48As/InP(001) by solid-source molecular beam epitaxy (MBE). The influence of the In0.52Al0.48As spacer layer thickness (SLT) on the structural and optical properties has been studied by means of transmission electron microscopy (TEM), atomic force microscopy (AFM) and photoluminescence (PL). A large full width at half maximum of the PL peak (FWHM=120 meV) has been observed on a structure with a single layer of wires. In contrast, a stacked structure with a SLT of 10 nm presents a PL peak FWHM reduced to 92 meV, which shows that the stacking process improves the wire size homogeneity. Polarized photoluminescence (PPL) experiments carried out on the stacked structures show a strong polarization anisotropy (35%) when the SLT is in the 10–15 nm range. On the contrary, for SLT equal to 5 nm, a weak degree of polarization is obtained (P∼6%) combined with a red shift of the PL line. This behaviour is attributed to vertical electronic coupling between the InAs QWRs when the SLT is lowered to within the 5 nm range.