A novel heterostructure with multilayer Stranski-Krastanov QDs heterogeneously coupled to Submonolayer QDs for enhanced optical and material characteristics

摘要

This paper presents a novel heterostructure with multilayer Stranski-Krastanov (SK) quantum dots (QDs) heterogeneously coupled to Submonolayer (SML) QDs that shows better performance in terms of both optical and material characteristics. The 2.5 ML InAs/GaAs multilayer SK QDs are grown on the 6 stack 0.3 ML InAs SML QDs using a Molecular Beam Epitaxy system. Multilayer includes single, bi, tri, penta, hepta and ten-layer SK QDs and a different growth mechanism is adapted to maintain the dot size similar in each layer irrespective of the residual strain from the bottom layers. Photoluminescence (PL) and high resolution X-ray Diffraction (HRXRD) experiments are done in order to analyze the optical and material characteristics of these grown heterostructures. PL results show that the ground state peak wavelength of SK QD for all the heterostructures is at ～1035 nm, which confirms a uniform dot size for all heterostructures. However, the sample with ten SK QD layers coupled to SML QD has the highest luminescence intensity, lowest full width half maxima (FWHM: ～50 meV), and highest activation energy (～397 meV). A peak at ～947 nm in the PL spectra confirms the presence of SML QDs and the tunneling of carriers from ground state of SML QD to excited state of SK QD is observed. HRXRD results show that the compressive strain experienced by the QDs is reducing with increase in the number of SK QD layers, which depicts ten SK QD layers coupled to SML QD heterostructure as the best even in terms of material characteristics.