Influence of Sb composition on the band alignment and optical characteristics of strain coupled vertically aligned InAs/GaAsSb quantum dots

Abstract

The influence of the Sb composition both on the band-alignment and the optical characteristics of strain-coupled vertically aligned InAs/GaAsSb Stranski-Krastanov (SK) quantum dots (QDs) embedded on six stack InAs/In_0.15Ga_0.85As Sub-monolayer (SML) matrix has been studied using nextnano simulation tool. A ten-layer strain-coupled InAs SK QDs electronically coupled to six stack SML QDs which has been the optimized structure is utilized in this study. Four different structures with Sb composition of 10%, 14%, 18% and 22% are chosen as a capping layer over InAs QDs and it is found that a transition in the band-alignment from type-I to type-II occurs when the Sb composition is increased above 14%. The optical characteristics have been simulated for these heterostructures which showed a red shift in the photoluminescence (PL) peak values with increase in the Sb composition. The PL peak value of ~1035 nm has been validated with the experimental PL data for the ten-layer InAs/GaAs SK QDs grown on six stack SML QDs without GaAsSb capping. With the similar dot size, the PL peak occurred at ~1115 nm, ~1159 nm, ~1209 nm and ~1284 nm, respectively, for 10%, 14%, 18% and 22% Sb composition structures. Investigation of electron and hole eigen states has been done for these structures. The usage of GaAsSb capping layer (strain reducing layer: SRL) over the InAs SK QDs allows an undulated strain transition from one SK QD layer to the other. The hydrostatic and the biaxial parts of the strain are estimated and a decrease in the hydrostatic compressive strain in the QDs has been observed with increase in the Sb composition. An increase in the biaxial strain with Sb composition has been noticed which result in lowering of the energy band gap and a red shift in the PL emission wavelength. Along with type-II band alignment, the low hydrostatic strain with 22% Sb composition facilitates lower dark current and also a red shifted PL results from ~1035 nm to ~1284 nm shows a promising direction for the realization of several optoelectronic device applications.