The role and growth of strain – reducing layer by molecular -beam epitaxy in a multi – stack InAs/(In,Ga)As sub - monolayer quantum dot heterostructure

Abstract

Abstract The present study focuses on a growth strategy to achieve a uniform (and larger) dot size distribution in a multi-stack InAs/InGaAs sub-monolayer (SML) quantum dot (QD) heterostructure by capping with a varying InxGa1-xAs (x = 0.15) layer thickness (Y). The InxGa1-xAs layer serves both as matrix medium for the dot growth and strain - reducing layer (SRL) to preserve the QD morphology from decomposition. The dots capped by an optimum SRL or capping layer (CL) thickness will alleviate from dot segregation or intermixing, surface diffusion and dot inhomogeneity effects, thus paving way to grow a nearly defect - free quantum dot heterostructure. The experimental calculations on low – temperature (19 K), high – excitation power (1.1 kW/cm2) photoluminescence (PL) revealed ground – state (GS) emission energies at 1.12, 1.14, 1.09 eV for 2, 4, and 6 ML SRL thickness respectively. While, the presence of QD excited state (ES) transitions has been analysed using PL - excitation (PLE) spectroscopy, as the CL will highly alter the band offsets as well as strain inside QDs. The interfacial structural quality, strain relaxation in QDs due to SRL was inspected through high-resolution X – ray diffraction (HRXRD) and Raman measurements. The self – consistent Schrodinger – Poisson solver based on 8 – band k.p formulation was used to evaluate the PL energy and strain profile as a comparison to experimental data. Hence, the sample containing 2 ML CL thickness showed superior results in terms of PL emission and strain, which leads towards the growth of uniform QDs for photodetector (PD) applications operating in the short – wave infrared (SWIR) regime (λ: 0.9 μm–2.5 μm, Energy: 1.377 eV - 0.495eV).