Theoretical investigation to study the influence of strain on the band lineups of core/shell nanostructures

Abstract

Abstract A class of quantum dots (QD) known as core–shell quantum dots (CSQDs) where a lower band gap material is enclosed by a higher band gap material, are highly confined nanoparticles, that project altered properties like enhanced carrier confinement, stability, and reduced recombination. The strain generated, due to the formation of a heterojunction-like structure near the CSQD boundary, has a direct impact on its opto-electronic properties by altering the band positions of the materials. In this work, we aimed to understand the impact of strain generated near such heterojunction due to the presence of two different materials as core and shell on its optical band lineup to comprehend the observed enhanced optical properties of such structures. Here, we have assumed a general model comprising ZnTe core surrounded by a ZnSe shell. Initially, to start, the CSQD structure was considered with a core size of 3 nm and a shell of 1.2 nm. A crossover from type-I to type-II in optical band line up was observed with an increase in shell thickness. The estimated value of the highest conduction band offset ∼60% was obtained for a shell width of 1.2 nm, i.e. the unstrained state, while the largest valence band offset ∼100% was obtained for the shell width of 1 nm.