Electrostatic fields and compositional fluctuations in (In,Ga)N/GaN multiple quantum wells grown by plasma-assisted molecular-beam epitaxy

We investigate the recombination mechanism in (In,Ga)N/GaN multiple quantum wells grown by plasma-assisted molecular-beam epitaxy. It is shown that for a thorough understanding of the spontaneous emission from these structures both electrostatic fields and compositional fluctuations have to be taken into account. The influence of the internal electrostatic fields is examined by continuous-wave and time-resolved photoluminescence as a function of well width. The transition energies and radiative decay times are shown to be in agreement with the quantum-confined Stark effect in these structures. The temperature dependence of the radiative decay time is measured to probe the dimensionality of the system. For a quantitative understanding, a rate-equation model is utilized for analyzing the data. At low temperatures, recombination is governed by localized states whereas for high temperatures extended states dominate. This analysis shows that the localization depth in these structures is below 25 meV.