Evidence for multiple chemical ordering in AlGaN grown by metalorganic chemical vapor deposition

In contrast to the GaN/InN system where there is a misfit of about 10%, the misfit between AlN and GaN is only 2.5%, and one would expect the growth of AlGaN to be more stable. In this work, it is shown that the growth of AlGaN can be complicated. Even in the low Al composition range, 10%–15%, many types of chemical ordering take place: AlN/GaN (1:1), $Al0.25Ga0.75N(3:1)$ only recently noticed in InGaN, and we show evidence for an additional type of chemical ordering which corresponds to $Al0.16Ga0.84N(10:2).$ The three types were found to coexist in the same layers, meaning that the growth may lead to nonhomogeneous composition in the AlGaN layer.