Optical polarization property of laterally aligned quantum dots

This work emphasizes on the optical polarization property of three kinds of quantum dot (QD) structures, namely, binary quantum dots (bi-QDs), linearly aligned quantum dots (LAQDs), and QDs aligned on a cross-hatch pattern. Such property was investigated by means of photoluminescence spectroscopy as well as theoretical calculation. It was found out from calculation that linear polarization degree (PD) of the LAQDs strongly depends on spacing, size, and number of QDs in the alignment. In particular, closer spacing, smaller dot size, or more number of QDs in the alignment gives rise to a higher PD value. For isolated QDs, the extent of shape isotropy strongly affects the PD. In the experimental point of view, optical properties of the three kinds of structures were investigated by means of temperature-dependent-, excitation-power-dependent-, and polarization-resolved photoluminescence spectroscopy. Measurements on a bi-QD sample and two LAQD samples reveal that the temperature-dependent PD for these nanostructures originates from coupling among the QDs. On the other hand, QDs on a cross-hatch pattern did not show the temperature-dependent behavior; the amount of PD that was observed for this type of sample merely comes from the shape anisotropy of individual QDs. By comparing these results, the physics behind the observed behaviors of these nanostructures is better understood and this will help produce higher-efficiency devices for the era of nanotechnology.