Influence of QD Morphology on Photoluminescence in GaSb/GaAs Multilayers*

Due to the predicted composition and strain dependence of type I versus type II band offsets, GaSb/GaAs quantum dots (QDs) are promising for a variety of optoelectronic applications. For GaSb/GaAs multilayers, atomic structures ranging from QDs, quantum rings and clusters have been observed, with photoluminescence (PL) energies ranging from 0.9 to 1.3eV. However, the association of these emission energies with specific nanostructure morphologies remains elusive. We investigate the structural and optical properties of GaSb/GaAs multilayers, with and without 3D nanostructures, using cross-sectional transmission electron microscopy, atom probe tomography (APT), and PL. In both cases, we find PL energies at 1.33eV and 1.49eV, which are attributed to 2D GaSb(As) layers and the GaAs matrix, respectively. For the case with 3D nanostructures, both individual QDs and circular arrangements of QDs, termed QD-rings, are observed. For both cases, Sb-rich cores are apparent, with x_Sb up to 0.40 (individual QDs) and 0.25 (QD-rings). Thus, we attribute 1.08 eV and 1.2 eV emissions to the individual QDs and QD-rings, respectively. Local measurements of the electronic states using scanning tunneling spectroscopy will also be presented.