Inhomogeneous broadening of direct optical transitions observed in photoluminescence and modulated reflectance in polar and non-polar InGaN quantum wells studied within the random quantum well model

In this work the random quantum well (RQW) model has been applied to analyze the broadening of interband transitions and the Stokes shift in InGaN/GaN QWs dedicated for green/blue lasers. Both polar and non-polar InGaN QWs were studied and compared for the same magnitudes of QW inhomogeneities (QW width and content fluctuations). Photoluminescence (PL) and electromodulated reflectance (ER) spectra have been simulated within the RQW model and compared between each other. It has been clearly shown that the built-in electric field is the parameter that shifts the emission wavelength to red but at the same time it enhances the broadening of optical transitions. In addition, it has been clearly shown that for polar QWs the Stokes shift can be very easily overestimated if PL spectra are compared with ER spectra since the intensity of fundamental transition observed in ER spectra significantly decreases with the increase in QW width. In this way ER signal related to excited states can dominate in ER spectra. This effect is strongly enhanced by QW inhomogeneities.