Investigations on heterogeneously coupled Submonolayer (SML) on Stranski-Krastanov (SK) quantum dot heterostructures with higher (0.1ML/sec) and lower (0.05ML/sec) growth rates

We are studying here the heterogeneously coupled Submonolayer (SML) on Stranski-Krastanov (SK) quantum dot (QD) heterostructures. The consolidation in SML on SK heterostructure has been observed by varying growth rate as 0.05 and 0.1 ML/sec. The barrier thickness between SK and SML QDs has also been varied as 5, 7.5, and 10 nm. Pphotoluminescence(PL) study shows transition of carriers with dot size distribution. The peak from SK QDs is prominent in PL spectra of both growth rate samples. The absence of SML peak from the PL might be due to the tunnelling of carriers from SML to SK QDs, which follows the SK ground energy states for recombination. SML peak is visible only in low growth rate sample for barrier thickness of 10 nm, as with higher barrier thickness there is reduction in the probability of tunnelling of carriers. Samples with lower growth rate shows bimodal dot size distribution at barrier thickness 7.5nm, whereas higher growth rate samples shows monomodal dot size distribution. Compressive strains were extracted from high-resolution X-Ray diffraction (HRXRD) measurement. From the HRXRD measurement, it has been found that the strain decreases with increasing barrier thickness. Low growth rate samples have less strain as compared to high growth rate samples. In the lower growth rate samples, PL peak is red shifted as compared to higher growth rate samples due to less strain in the heterostructures and larger size QDs. Therefore, this study will be useful for advanced optoelectronic applications.