  In this work the broadening of interband transitions in InGaN/GaN quantum
wells (QWs) resulting from structural inhomogeneities is analyzed. The role of
polarization-induced electric field in the mechanism behind the inhomogeneous
broadening observed in photoluminescence (PL) and electromodulated reflectance
(ER) spectra of InGaN QWs dedicated to green/blue lasers is explained. Spectra
of both polar and non-polar QWs are simulated within the random QW model
distinguishing contributions of individual transitions taking into account QW
inhomogeneities (QW width and indium content fluctuations). On this basis we
interpret the ER and PL spectra measured for a polar multiple QW InGaN/GaN
structure. The built-in electric field shifts the emission wavelength to red,
and enhances the broadening of optical transitions. It is clearly shown that
for polar QWs the Stokes shift can be easily overestimated if PL spectra are
compared with ER spectra since the intensity of the fundamental transition
observed in ER spectra significantly decreases with the increase in QW width.
In this way ER signal related to excited states start to dominate. This effect
is strongly enhanced by QW inhomogeneities.
