Light-emitting and laser diodes for green to near-UV region are based on quantum structures with InGaN active region. However, characteristics of devices with multiple quantum wells (MQWs) are not clear so far. One of the most important characteristics of MQWs is the well width. With increasing the well width the emission from MQWs is affected not only by quantum confinement, but by intricate processes due to spinodal decomposition of In and built-in electrical field as well. To maximise spontaneous and stimulated emission, underlying physics should be cleared out and the growth conditions and structure of the MQWs are to be optimised.
Here we present results on high-excitation luminescence spectroscopy in In0.15Ga0.85N/GaN MQWs with various well width. High excitation conditions results in screening of built-in electrical field by free carriers and allowed us to determine the influence of In segregation on optical properties. Optimal quantum well thickness for InGaN/GaN lasing structures is obtained for the well width d = 3 nm. With increasing the well thickness, indium-rich clusters increase in size that results in an occurrence of deeper localization states with longer depopulation time and conventional degradation of the material. Meanwhile in thin wells, increased role of the interfaces states results in enhanced nonradiative recombination.

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