Abstract
The temperature dependence of the formation of nano-scale indium clusters inInAlGaN quaternary alloys, which are grown by metalorganic chemical vapourdeposition on GaN/Si(111) epilayers, is investigated. Firm evidence is provided tosupport the existence of phase separation, or nano-scale In-rich clusters, by thecombined results of high-resolution transmission electron microscopy (HRTEM),high-resolution x-ray diffraction (HRXRD) and micro-Raman spectra. The resultsof HRXRD and Raman spectra indicate that the degree of phase separation isstrong and the number of In clusters in the InAlGaN layers on silicon substrate ishigher at lower growth temperatures than that at higher growth temperatures,which limits the In and Al incorporated into the InAlGaN quaternary alloys. Thedetailed mechanism of luminescence in this system is studied by low temperaturephotoluminescence (LT-PL). We conclude that the ultraviolet (UV) emission observed inthe quaternary InAlGaN alloys arises from the matrix of a random alloy, and thesecond emission peak in the blue–green region results from the nano-scale indiumclusters.
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