  In this paper we present a detailed analysis of the structural, electronic,
and optical properties of an $m$-plane (In,Ga)N/GaN quantum well structure
grown by metal organic vapor phase epitaxy. The sample has been structurally
characterized by x-ray diffraction, scanning transmission electron microscopy,
and 3D atom probe tomography. The optical properties of the sample have been
studied by photoluminescence (PL), time-resolved PL spectroscopy, and polarized
PL excitation spectroscopy. The PL spectrum consisted of a very broad PL line
with a high degree of optical linear polarization. To understand the optical
properties we have performed atomistic tight-binding calculations, and based on
our initial atom probe tomography data, the model includes the effects of
strain and built-in field variations arising from random alloy fluctuations.
Furthermore, we included Coulomb effects in the calculations. Our microscopic
theoretical description reveals strong hole wave function localization effects
due to random alloy fluctuations, resulting in strong variations in ground
state energies and consequently the corresponding transition energies. This is
consistent with the experimentally observed broad PL peak. Furthermore, when
including Coulomb contributions in the calculations we find strong exciton
localization effects which explain the form of the PL decay transients.
Additionally, the theoretical results confirm the experimentally observed high
degree of optical linear polarization. Overall, the theoretical data are in
very good agreement with the experimental findings, highlighting the strong
impact of the microscopic alloy structure on the optoelectronic properties of
these systems.
