Origin of the near-band-edge luminescence in MgxZn1-xO alloys

The carrier dynamics of donor-bound and free excitons, localized in the alloy disorder potential, were investigated for MgxZn1-xO (0.08 <x <0.33) thin films. The measured transients show a fast decrease in the luminescence intensity within the first nanoseconds, followed by a slow, strongly nonexponential decay. Shortly after the excitation pulse, the time-delayed spectra are dominated by the (D-0,X) recombination. With increasing time, the free exciton recombination becomes visible on the high-energy side, dominating the spectra at large times after the excitation pulse. By fitting the transients with nonexponential model decay functions, we can deconvolve the luminescence spectra. As expected, the mean decay time of the excitons localized in the alloy disorder potential significantly increases with increasing Mg content.