MBE growth and properties of low-density InAs/GaAs quantum dot structures

We present the results of a comprehensive study carried out on morphological, structural and optical properties of InAs/GaAs quantum dot structures grown by Molecular Beam Epitaxy. InAs quantum dots were deposited at low growth rate and high growth temperature and were capped with InGaAs upper confining layers. Owing to these particular design and growth parameters, quantum dot densities are in the order of 4-5x10⁹ cm^-2 with emission wavelengths ranging from 1.20 to 1.33 Aμm at 10 K, features that make these structures interesting for single-photon operation at telecom wavelength. High resolution structural techniques show that In content and composition profiles in the structures depend on the particular epitaxial growth conditions used to reduce the density of quantum dots. Carrier recombination dynamics in quantum dots is studied by analysing the integrated photoluminescence (PL) intensity and recombination times as functions of the temperature. Arrhenius plots of the integrated PL show two activation energies implying two decay processes. The first one is associated to thermal escape of carriers from quantum dot to wetting layer states; the second one is consistent with the thermal population of quantum dot dark states, as suggested by time resolved PL measurements.