Electronic and optical properties of polar, semi- and non-polar InGaN QDs: the role of second-order piezoelectric effects

Abstract

In this work, we study the impact of second-order piezoelectricity on total built-in field, electronic and optical properties of InGaN/GaN quantum dots grown along different crystallographic directions. The calculations are carried out in the frame of a symmetry-adapted k · p model. Special attention is paid to the impact of Coulomb effects (excitonic effects) on the results. Overall our calculations reveal that for a c-plane system with 20% In, Coulomb effects and second-order piezoelectric effects are of secondary importance for the electron hole wave function overlap. For the semi- and non-polar systems, we find that Coulomb effects are essential to achieve an accurate description of their electron and hole wave function overlap. This stems from the observation that in the here studied systems the built-in field is strongly reduced compared to the c-plane dot. Overall, our calculations reveal that second-order piezoelectricity significantly affects the results in the non-polar case, resulting for instance in a noticeably larger oscillator strength and therefore shorter radiative lifetimes compared to the studied semi-polar system. The here calculated radiative lifetimes of the semi- and non-polar structures are in good agreement with reported experimental literature data.