The information on the variations of indium composition, aggregation size, and quantum-well width is crucially important for understanding the optical properties and, hence, fabricating efficient light-emitting devices. Our results showed that spinodal decomposition could occur in InGaN/GaN multiple quantum wells with indium content in the range of 15%-25% ͑grown with metal-organic chemical-vapor deposition͒. A lower nominal indium content led to a better confinement of indium-rich clusters within InGaN quantum wells. The InGaN/GaN interfaces became more diffusive, and indium-rich aggregates extended into GaN barriers with increasing indium content. It was also observed that indium-rich precipitates with diameter ranging from 5 to 12 nm preferred aggregating near V-shaped defects.

Multiple-component decays of photoluminescence (PL) in InGaN/GaN quantum wells have been widely reported. However, their physical interpretations have not been well discussed yet. Based on wavelength-dependent and temperature-varying time-resolved PL measurements, the mechanism of carrier transport among different levels of localized states (spatially distributed) in such an indium aggregated structure was proposed for interpreting the early-stage fast decay, delayed slow rise, and extended slow decay of PL intensity. Three samples of the same quantum well geometry but different nominal indium contents, and hence different degrees of indium aggregation and carrier localization, were compared. The process of carrier transport was enhanced with a certain amount of thermal energy for overcoming potential barriers between spatially distributed potential minimums. In samples of higher indium contents, more complicated carrier localization potential structures led to enhanced carrier transport activities. Free exciton behaviors of the three samples at high temperatures are consistent with previously reported transmission electron microscopy results.

The results of photoluminescence (PL), detection-energy-dependent photoluminescence excitation (DEDPLE), excitation-energy-dependent photoluminescence (EEDPL), and strain state analysis (SSA) of three InGaN/GaN quantum-well (QW) samples with silicon doping in the well, barrier and an undoped structure are compared. The SSA images show strongly clustering nanostructures in the barrier-doped sample and relatively weaker composition fluctuations in the undoped and well-doped samples. Differences in silicon doping between the samples give rise to the differences in DEDPLE and EEDPL spectra, as a result of the differences in carrier localization. In addition, the PL results provide us clues for speculating that the S-shaped PL peak position behavior is dominated by the quantum-confined Stark effect in an undoped InGaN/GaN QW structure.

Based on wavelength-dependent and temperature-varying time-resolved photoluminescence ͑PL͒ measurements, the mechanism of carrier transport among different levels of localized states ͑spatially distributed͒ in an InGaN/GaN quantum well structure was proposed for interpreting the early-stage fast decay, delayed slow rise, and extended slow decay of PL intensity. The process of carrier transport was enhanced with a certain amount of thermal energy for overcoming potential barriers between spatially distributed potential minimums. With carrier supply in the carrier transport process, the extended PL decay time at wavelengths corresponding to deeply localized states can be as large as 80 ns.