Effects of rapid thermal annealing on the optical properties of InAs quantum dots with asymmetric ingaas layers

Photoluminescence (PL) spectroscopy was used to investigate the effects of rapid thermal annealing (RTA) on self-assembled InAs quantum dot (QD) structures having asymmetric In _0.15Ga _0.85As layers. After RTA, the PL spectra from the InAs QDs were blue-shifted and showed significant narrowing of the PL linewidth, compared with as-grown (unannealed) samples. In particular, the PL peak positions of the annealed QD samples, which had one InAs QD layer inserted between two In _0.15Ga _0.85As layers, were blue-shifted about 200 meV at annealing temperatures up to 750°C. This was about twice as large as the blue-shift observed for a QD sample with three InAs QD layers separated by an In _0.15Ga _0.85As/GaAs heteorostructure. The suppression of the blue-shift is attributed to reduced intermixing of indium atoms under the strain field within or nearby the QDs. The energy-level spacing between the ground states and the first excited states decreased as the annealing temperature was increased. This reduction in energy-level spacing is largely related to changes in the QD shape and size, especially changes in the aspect ratio (height/width) that result from annealing.