InGaN-based multiple quantum wells (MQWs) are the key structures for high efficiency, long lifetime violet, blue, and green light emitting diodes and laser diodes. During the epitaxial growth of InGaN/GaN structures and during the fabrication of devices, active layers undergo several high-temperature treatments. The distribution of the indium composition and the strain in quantum wells may be changed due to spinodal decomposition and interdiffusion of indium and gallium across the interface of quantum well and barrier after these thermal treatments. This can lead to a change of emission properties of MQWs.
Here we present results on temperature-dependent site-selective photoluminescence, photoluminescence excitation and time-resolved luminescence study of three In0.15Ga0.85N/GaN MQWs with well-widths of 2, 3, 4-nm, upon thermal annealing at 800 0C for 30 min. Our results imply on nontrivial dependence of MQWs emission properties upon thermal annealing. Blueshift of luminescence and pronounced changes in the absorbance are attributed to domination of spinodal decomposition for the thin wells. While pronounced redshift in luminescence and increase in the excitation lifetime is attributed to prevalence of strain-induced field-effect for the thicker MQWs. These changes are related to the enhancement of indium segregation and rise in the built-in electric field effect of as-grown samples of various thicknesses.

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