Phase separation and ordering in InGaN alloys grown by molecular beam epitaxy

In this study, we investigated phase separation and long-range atomic ordering phenomena in InGaN alloys produced by molecular beam epitaxy. Films grown at substrate temperatures of $\text{700–750\hspace{0.17em}°}\mathrm{C}$ with indium concentration higher than 35% showed phase separation, in good agreement with thermodynamic predictions for spinodal decomposition. Films grown at lower substrate temperatures (650–$\text{675\hspace{0.17em}°}\mathrm{C})$ revealed compositional inhomogeneity when the indium content was larger than 25%. These films, upon annealing to $\text{725\hspace{0.17em}°}\mathrm{C},$ underwent phase separation, similar to those grown at the same temperature. The InGaN films also exhibited long-range atomic ordering. The ordering parameter was found to increase with the growth rate of the films, consistent with the notion that ordering is induced at the growth surface. The ordered phase was found to be stable up to annealing temperatures of $\text{725 °}\mathrm{C}.$ A competition between ordering and phase separation has been observed, suggesting that the driving force for both phenomena is lattice strain in the alloy.