Localization versus field effects in single InGaN quantum wells

The optical properties of InxGa1-xN quantum wells (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)less than or equal to6 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)greater than or equal to8 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)less than or equal to6 nm and the dominance of field effects for L(z)greater than or equal to8 nm. (C) 2004 American Institute of Physics.