Carrier localization in (InGa)(AsN) alloys

We investigate the origin of radiative recombination in (InGa)(AsN)/GaAs single quantum wells by means of continuous wave and time-resolved photoluminescence (PL) measurements. Samples with different indium and nitrogen concentration were investigated. An analysis of the whole set of data for different excitation densities and lattice temperatures, T, is reported. This analysis provides insights into radiative and non-radiative processes ruling the recombination dynamics and shows the predominant contribution of localized state emission at low T. The nature of these states is further studied by measuring the time necessary (rise time) for their population. We find that the PL rise time in (InGa)(AsN) is independent of temperature and detection energy, thus being not conclusive about the origin of the states involved in the emission processes. On the contrary, magneto-PL measurements show that the shift of the PL peak energy induced by a magnetic field, B, decreases sizably and changes its dependence on B from linear to quadratic when going from low to high temperature. This counterintuitive result shows that radiative recombination at low temperature (T < 100 K) is not excitonic, contrary to previous assignments, and is due to loosely bound electron-hole pairs in which one carrier is localized by N-induced potential fluctuations and the other carrier is delocalized.