  We investigate the radiative and nonradiative recombination processes in
planar (In,Ga)N/GaN(0001) quantum wells and (In,Ga)N quantum disks embedded in
GaN$(000\bar{1})$ nanowires using photoluminescence spectroscopy under both
continuous-wave and pulsed excitation. The photoluminescence intensities of
these two samples quench only slightly between 10 and 300 K, which is commonly
taken as evidence for high internal quantum efficiencies. However, a
side-by-side comparison shows that the absolute intensity of the Ga-polar
quantum wells is two orders of magnitude higher than that of the N-polar
quantum disks. A similar difference is observed for the initial decay time of
photoluminescence transients obtained by time-resolved measurements, indicating
the presence of a highly efficient nonradiative decay channel for the quantum
disks. In apparent contradiction to this conjecture, the decay of both samples
is observed to slow down dramatically after the initial rapid decay.
Independent of temperature, the transients approach a power law for longer
decay times, reflecting that recombination occurs between individual electrons
and holes with varying spatial separation. Employing a coupled system of
stochastic integro-differential equations taking into account both radiative
and nonradiative Shockley-Read-Hall recombination of spatially separate
electrons and holes as well as their diffusion, we obtain simulated transients
matching the experimentally obtained ones. The results reveal that even
dominant nonradiative recombination conserves the power law decay for
(In,Ga)N/GaN{0001} quantum wells and disks.
