Study on optical properties and strain distribution of InAs/InGaAs sub-monolayer quantum dot heterostructure with multiple stacking layers

This study examines the photoluminescence (PL) properties and strain distribution in InAs/InGaAs heterostructure for varying number of sub-monolayer (SML) quantum dot stacks (nSML). High resolution x-ray diffraction (HRXRD) probes the strain effects, whereas PL spectroscopy evaluated the optical response. The ground-state transition energies calculated from PL experiments were found to be 1.19, 1.13, 1.11, 1.12 eV for 4, 6, 8 and 10 stacks respectively. It was observed that, with the increasing nSML, the PL peak emission energy has an initial blue shift and later a red shift, due to build-up of strain energy propagating from the bottom layers of InAs quantum dots (QDs). The activation energies (Ea) calculated from temperature-dependent PL (TDPL) measurements are 414, 279, 260 and 231 meV for 4, 6, 8 and 10 stacks respectively. The Raman characterization results explores on the strain relaxation effects by observing the shift and broadening in TO and LO phonon peaks of GaAs bulk material. The strain energy distribution along the growth direction (z-direction) was studied using nextnano++ simulations. The relative change in hydrostatic and biaxial strain at a particular z - position was calculated to be 3.2% and 5.5% respectively These strain components are of prime importance in understanding the position of conduction and valence band energy levels and finally the band gap energy. Thus, with these articulated results, we conclude that sample with 6 SML stacks is the optimum choice for fabricating optoelectronic devices operating in long range infrared telecommunication regime.