Localization versus field effects in single InGaN quantum wells

The optical properties of ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ quantum wells $\text{(x=0.13)}$ have been studied by cathodoluminescence (CL) spectroscopy. A blueshift of the quantum well emission is observed with increasing excitation density, which can be explained by considering (a) band filling of in-plane potential fluctuations caused by compositional inhomogeneities, or (b) screening of piezoelectric fields inside the well. We have used time-resolved CL spectroscopy to distinguish between the two effects. The onset and decay of the relaxation and recombination kinetics are measured by using rectangular excitation pulses with ultrafast on and off switching and with pulse lengths sufficiently long to ensure excitation into quasi-steady-state conditions. For well widths of $L_z\text{⩽6\hspace{0.17em}}\mathrm{nm},$ a redshift is observed after the electron beam is switched on and a further redshift occurs after the electron beam is switched off. For $L_z\text{⩾8\hspace{0.17em}}\mathrm{nm},$ a blueshift is observed after the electron beam is switched on and a redshift is observed after the electron beam is switched off. We attribute the different behaviors to the dominance of localization effects for $L_z\text{⩽6\hspace{0.17em}}\mathrm{nm}$ and the dominance of field effects for $L_z\text{⩾8\hspace{0.17em}}\mathrm{nm}.$