Use of polytypes to control crystallographic orientation of GaN

Many characteristics of epitaxially grown films depend sensitively on their orientations. In most cases, orientation is uniquely determined by that of the substrate, a correlation established by energy minimization. Here, we show that substrate-independent control of orientation is possible by paths available in kinetically limited growth regimes for materials exhibiting polytypism. Demonstrated for GaN, our intriguing results provide fundamentally new insight into controlling one of the most important structural parameters of epitaxial films. This approach might be readily extended to other III-nitrides and ZnO, which also exhibit polytypism. Our procedures can be easily applied to tailor characteristics of epitaxial films, allowing investigations of new properties such as unipolarity.