A comparative study of Dots-in-a-Double-Well (DDWELL) heterostructures with SK, SML and coupled SK-on-SML as active region

Abstract

A comparative study of Stranski-Krastanov (SK), sub-monolayer (SML) and coupled SK on SML InAs quantum dots as active region in InGaAs/GaAs/AlGaAs DDWELL heterostructure was done. Incorporation of additional high band gap confinement enhancing (CE) Al_xGa_1-xAs barrier helps to create new energy levels, increase the absorption coefficient, reduce dark current and improve crystalline quality of the heterostructure. This is because of the CE barrier which reduces In-adatom out-diffusion. Three different DDWELL heterostructure A, B and C with active regions as SK, SML and SK on SML respectively, had been modelled using the Nextnano simulation tool keeping all other parameters same. Photoluminescence (PL) emission wavelength, biaxial strains and hydrostatic strain profiles of heterostructures A, B and C were compared. Hydrostatic strain with less magnitude leads to better carrier confinement within the conduction band, and biaxial strain with high magnitude increases splitting between heavy-hole and light- hole bands, generating a red-shift in PL emission wavelength. It can be observed from the computed result that biaxial and hydrostatic strain in the SK QD are enhanced in structure C compared to A. Likewise, biaxial strain and hydrostatic strain in the SML QD stacks are enhanced in structure C compared to B. PL emission wavelength of structures A, B, and C were observed to be 1116nm, 864nm and 1170nm respectively. Therefore, structure C exhibits minimum strain among the heterostructures and highest PL emission wavelength for SWIR applications.