Atomistic theoretical study of electronic and polarization properties of single and vertically stacked elliptical InAs quantum dots

Abstract

The demonstration of isotropic polarization response from semiconductor quantum dots (QDs) is a crucial step towards the design of several optoelectronic technologies. Among many parameters that impact the degree of polarization (DOP${}_{[\stackrel{P\vec}{n}]}$) of a QD system, the shape asymmetry is a critical factor. We perform multi-million-atom simulations to study the impact of the elliptical shapes on the electronic and polarization properties of single and vertically stacked InAs QDs. The comparison between a low aspect ratio (AR) and a high AR QD reveals that the electronic and the polarization properties strongly depend on the AR of the QD; the elongation of a tall QD allows tuning of the DOP${}_{[\stackrel{P\vec}{n}]}$ over a much wider range. We then extend our analysis to an experimentally reported vertical stack of nine QDs (9-VSQDs) that has shown significant potential to achieve isotropic polarization properties. We analyze the contribution from the shape asymmetry in the large, experimentally measured, in-plane polarization anisotropy. Our analysis shows that the orientation of the base elongation controls the sign of the DOP${}_{[\stackrel{P\vec}{n}]}$; however, the magnitude of the base elongation has only a very little impact on the magnitude of the DOP${}_{[\stackrel{P\vec}{n}]}$. We further predict that the elliptical shape of the 9-VSQDs can only tune either DOP${}_{[110]}$ or DOP${}_{[\overline{1}10]}$ for the isotropic response. Our model results, in agreement with the TEM findings, suggest that the experimentally grown 9-VSQDs has either a circular or a slightly [$\overline{1}$10] elongated base. Overall, the detailed investigation of DOP${}_{[\stackrel{P\vec}{n}]}$ as a function of the QD shape asymmetry provides a theoretical guidance for the continuing experimental efforts to achieve tailored polarization properties from QD nanostructures for the design of optical devices.