Influence of dot size distribution and interlayer thickness on the optical property of closely stacked InAs/GaAs quantum dots with growth interruption

Abstract

We investigated the effect of dot size distribution and interlayer thickness on the optical property of closely stacked self-assembled InAs/GaAs quantum dot (QD) structures with growth interruption for 30 s using an As2 source. The structural property was optimized by changing the growth parameters, such as growth temperature, growth time and group III/V ratio. As the stacking number was increased, the size of truncated pyramid-shaped QDs became larger in both height and width, maintaining an on-top vertical alignment with a dot density of ∼5.2–5.9 × 1010 cm−2. Compared to the single QD layer, five closely stacked QDs with the GaAs interlayer are found to exhibit a significant improvement of their photoluminescent (PL) intensity, indicating a slight shift of the PL peak position toward the high-energy side. The use of a thin GaAs interlayer of 3 nm in the QDs enhanced the blue shift, which is attributed to the dominant strain-induced intermixing or loss of indium atoms in the InAs QD layers. For the interlayer thicker than about 7 nm, the blue shifts are correlated to the dominant high-energy excited state transitions due to the successive state filling of the ground and higher excited states in the QDs. The energy separation of double PL peaks, originating from two different excited states, was kept at around 50 meV at room temperature. A possible mechanism concerning this phenomenon was also discussed.