A theoretical study on strain and optical property of InAs SK quantum dot with varying capping in SK-SML coupled surface quantum dot heterostructure

In the past decade, surface quantum dots (SQDs) have been thoroughly investigated for sensing applications. The SQDs suffer from the limitations of non-uniformity dot distribution and weak oscillator strength, which affect their response to ambient contaminants. We have achieved uniformity by coupling buried quantum dots (BQDs) with SQDs. Moreover, BQDs provide additional carriers to SQDs for enhancing sensitivity. In this study, we have theoretically investigated the impact of varying the capping material of BQDs on their strain and optical properties. Investigations have been carried out with three samples having different capping materials as GaAs (sample A1), InGaAs (sample A2), and InAlGaAs (sample A3). A decreasing trend in the magnitude of hydrostatic strain and an increasing trend in biaxial strain inside the BQD from samples A1-A3 is observed. With a decrease in hydrostatic strain, the conduction band eigenstate lowers towards the band edge resulting in a lowering bandgap. With an increase in biaxial strain, the bandgap lowers due to the heavy hole (HH) and light hole (LH) band splitting. The lowering of the bandgap enhances the luminescence of BQD in sample A3. The computed photo-luminescence (PL) emission wavelength is found to be 1547 nm, 1558 nm, and 1568 nm for GaAs, InAlGaAs, and InGaAs capping respectively. The lowering in the bandgap of BQD leads to band alignment between SQD and BQDs, which may improve the carrier communication between these layers and become a promising candidate for better carrier reservoirs for SQDs in sensor applications.