Under Vacuum Photoluminescence Study of Vertically Stacked InAs/GaAs Quantum Dots

This work presents a study of photoluminescence (PL) in vacuum from vertically stacked InAs/GaAs quantum dots on (100) N+ oriented GaAs substrate. A PL system in ultra-high vacuum that was coupled onto a molecular beam epitaxy (MBE) chamber was used in order to avoid the oxidation of the quantum dots. After carrying out the PL of the first layer, the same sample has been returned back to the MBE chamber to grow a second, third, forth and fifth layer of QDs, where after every layer the sample has been taken out of the MBE to the PL system. A clear double peak structure revealing a bimodel size distribution of the QDs has been shown by the power and the temperature dependent PL studies. This bimodel size distribution of the QDs has been also confirmed by an atomic force microscopy (AFM) image. A blue shift in the PL was observed after the deposition of the second layer due to the generation of a strain field which results in the formation of a second QD layer with different structure and dimensions compared to the first QD layer. The present observations can help improve understanding the dependence of the optical properties of InAs/GaAs QDs on inter-diffusion of In and Ga atoms during the growth of a new layer due to annealing effect.