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.

Thermal stability of InxGa1-xN/GaN multiple quantum wells with InN mole fraction of ∼0.23 and ∼0.30 was investigated by postgrowth thermal annealing. Low temperature photoluminescence spectroscopy was employed to determine the temperature dependence of the interdiffusion coefficient of In and Ga in InGaN/GaN quantum wells. The interdiffusion process is characterized by a single activation energy of about 3.4±0.5 eV and governed by vacancy-controlled second-nearest-neighbor hopping. Due to composition inhomogeneity, lower diffusivity is observed at the early stage of thermal annealing.

The temperature dependence of the radiative recombination zone in InGaN/GaN multiple quantum well light-emitting diodes is investigated. From the electroluminescence spectra measured at various temperatures, it is found that there are two peaks at about 400 and 460 nm, which can be assigned as Mg-related and quantum well transitions, respectively. The behavior of these two peaks with temperature is modeled by the two rate equation. Based on this model, we deduce the activation energy of Mg in GaN films to be about 126 meV, which is consistent with reported results obtained by other techniques.

We report the study results of an InGaN/GaN multiple quantum well structure with a nominal indium content of 25%. The high-resolution transmission electron microscopy and x-ray diffraction show clear indium aggregation and phase separation. Stimulated emission data always show two major peaks in spectrum. The long-͑short-͒ wavelength peak is assigned to the recombination of localized state carriers ͑free carriers͒. At low temperatures or optical pump levels, the localized-state recombination dominates the stimulated emission; however, at high temperatures or pump levels, the free-carrier recombination becomes dominant. The peak position corresponding to localized states changes little in spectrum as temperature or pump level varies. This result is attributed to carrier overflow, strain relaxation, and carrier shielding in increasing temperature or carrier supply.

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