Enhanced performance of InAs/InGaAs dot-in-well heterostructure through varying capping thickness

This study is focused on structural and optical properties of multilayer InAs/InGaAs dot-in-a-well (DWELL) heterostructure with varying capping layer thickness. Two samples A and B are considered with 2 monolayer (ML) InAs quantum dots (QDs). The top InGaAs capping layer thickness is varied from 6 to 8 nm from sample A to B, whereas the lower well thickness was kept constant at 2 nm. The ground-state peak in the photoluminescence (PL) spectra shows a blue shift with increased capping layer thickness (sample A: 1148 nm, sample B: 1140 nm). This blue shift is due to the increased well layer thickness, which leads to higher strain and shrinkage in dot size. The activation energy (Ea) is calculated from the temperature dependent PL results using the Arrhenius equation. The activation energy of sample A and B are 181 meV and 152 meV respectively. The higher activation energy leads to a reduction in dark current, which affirms that sample A would be better for the device application. Raman spectroscopy is also carried out to observe different phonon peaks in both samples. For sample B, the broadening of the GaAs transverse optic (TO) mode is higher, which may lead to increased non-radiative carrier recombination. It may also lead to reduction of carrier lifetime. Hence, sample A with lower well thickness would be useful in optoelectronic device application because of its improved optical characteristics.