Fine-tuning of electron Eigen energy states in GaAs1-xNx capped InAs sub-monolayer quantum dots

The capping layer (CL) overgrowth process is a very mandate step to preserve the quantum dot (QD) basic parameters necessary for enhanced device performance. It is a well-known aspect that the strain fields inside QD(CL) gets altered both along [100] (perpendicular) and [001] (parallel) directions, when employed with an appropriate CL thickness and composition (%). In this study, we report on the InAs Sub-monolayer (SML) QDs capped by a tensile-strained CL: GaAs1−xNx (2 ML thick), to lessen the net compressive strain in the system. A 8-band k.p simulation was performed in this regard to understand the change in optical and strain properties, for varying dilute Nx contents (x): 1.5, 1.8, 2.2 and 2.5% respectively. Firstly, the hydrostatic (biaxial) strain along [001] inside QD region increases (decreases) with increasing x(%) and this supposedly should blueshift photoluminescence (PL) spectra. Secondly, the changes in band structure across the conduction and valence bands (CB, VB) gave some clear insights on the PL redshift. The CB minima in CL gets lowered, accounting for reduced carrier confinement and not due to the strain counterparts. The tensile strain nature of CL has a larger band gap bowing parameter that helps in this stronger redshift in PL energy. By this lowering of CB energy in CL, the electron eigen levels inside QD shift downwards, reducing the bandgap of the same. Finally, the simulated PL energy values at 19 K for varying N% was found to be 1.06, 1.02, 0.96, and 0.92 eV finding it suitable for laser applications.