Electronic structure and optical transitions in InAsSb/InGaAs quantum dots

Self-assembled InAsSb/InGaAs quantum dots are candidates for optical detectors and emitters in the 2-5 micron band with a wide range of applications for atmospherical chemistry studies. While photoluminescence peaks at wavelengths as high as 2.2 /spl mu/m have been measured in InAsSb dots (Qiu and Uhl, 2004), the present study aims at determining the maximum wavelength theoretically achievable. The energy band gap of unstrained bulk InAs/sub 1-x/Sb/sub x/ is smallest for x=0.62 but biaxial strain for bulk InAs/sub 1-x/Sb/sub x/ grown on In/sub 0.53/Ga/sub 0.47/As shifts the energy gap to higher energies and the smallest band gap is reached for x=0.51, which seems therefore to be the preferred concentration for long wavelength optical devices. We next examine how the electronic confinement in the quantum dots modifies these simple considerations. We have calculated the electronic structure of lens shaped InAs/sub 1-x/Sb/sub x/ quantum dots with diameter 37 nm and height 4 nm embedded in a In/sub 0.53/Ga/sub 0.47/As matrix of thickness 7 nm and lattice matched to an InP buffer. The relaxed atomic positions were determined by minimizing the elastic energy obtained from a valence force field description of the inter-atomic interaction. The electronic structure was calculated with an empirical tight binding approach with the parameters obtained from (Jancu et al., 1998). We will further show the variation of the exciton energy and oscillator strength as a function of Sb concentration throughout the region where the electron is confined in the In/sub 0.53/Ga/sub 0.47/As buffer material.