Influence of composition and well-width fluctuations on optical gain in (In, Ga)N multiple quantum wells

The influence of composition and well-width fluctuations on the optical gai n in (In, Ga)N multiple quantum wells for different barrier dopings and com positions is studied under quasistationary conditions. Systematic temperatu re- and excitation-density-dependent gain measurements were performed by me ans of the variable-stripe-length method. The correlation between optical p roperties such as gain or temperature behaviour of the laser threshold and the crystal quality of the samples is demonstrated. In addition, by means o f photoluminescence measurements, the temperature dependence of the quantum efficiency is determined, which gives information on the activation proces ses to nonradiative recombination channels. Thermal activation energies obt ained from these measurements can be correlated with the depth of potential minima caused by composition fluctuations in the quantum well. The experim ental temperature-dependent threshold density and gain can be successfully explained by use of a simple model of band-to-band transitions considering localization effects.