  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.
