Origin of the Broad Lifetime Distribution of Localized Excitons in InGaN/GaN Quantum Dots

TL;DR

This paper explains the broad distribution of exciton lifetimes in InGaN/GaN quantum dots by deriving a decay-time distribution function and showing how internal fields and structural variations cause diverse radiative lifetimes.

Contribution

It introduces an energy-dependent decay-time distribution function and demonstrates how built-in fields and structural variations lead to broad lifetime distributions in quantum dots.

Findings

Decay-time distribution function matches single-QD measurements.

Built-in fields cause sensitive dependence of lifetimes on QD geometry.

Structural variations lead to broad lifetime distributions.

Abstract

We derive an energy-dependent decay-time distribution function from the multi-exponential decay of the ensemble photoluminescence (PL) of InGaN/GaN quantum dots (QDs), which agrees well with recently published single-QD time-resolved PL measurements. Using eight-band k.p modelling, we show that the built-in piezo- and pyroelectric fields within the QDs cause a sensitive dependence of the radiative lifetimes on the exact QD geometry and composition. Moreover, the radiative lifetimes also depend heavily on the composition of the direct surrounding of the QDs. A broad lifetime distribution occurs even for moderate variations of the QD structure. Thus, for unscreened fields a multi-exponential decay of the ensemble PL is generally expected in this material system.