Growth and optical properties of self-assembled type II GaSb/GaAs quantum dots

We report the realization of quantum-sized GaSb dots, of small diameter (~25 nm), on GaAs by molecular beam epitaxy in the Stranski-Krastanow growth mode. With the deposition of 3.1 mono-layers (MLs) GaSb, the average diameter and height of GaSb quantum dot (QD) are 26 nm and 6.2 nm, respectively. In addition, density control was systematically achieved between 2.6×10⁹ and 1.2×10¹⁰ cm^-2 by carefully choosing the amount of GaSb deposited from 2.5 to 3.1 ML. The growth mechanism are discussed in detail. Also, we identify the QD luminescence by photoluminescence obtained at different excitation energies and densities. We show how for these structures not only the spectral position of peaks, but also their relative intensities are critically dependent upon the density of photo-generated carriers. Photoluminescence excitation (PLE) measurements confirm our assignment of the QD related peaks and a feature 25-27 meV higher in energy than the PLE detection energy is discussed in terms of phonon relaxation