Isotropic and anisotropic growth models for the sublimation vapour transport process.

The sublimation vapour transport method is a widely used technique for the production of optoelectronic materials, such as aluminium nitride (AIN). One-step reaction with two vapour species, i.e. aluminium (Al) vapour and nitrogen (N2) gas, is widely assumed and diffusion-controlled growth mechanism with thermodynamic equilibrium calculations is usually used in the open literature. In this paper, the diffusion transport model, aluminium vapour dominated model and nitrogen dominated model are summarized/proposed. The operating conditions in which different models can be employed are identified. The predicted growth rates using different models are compared with each other and with the experimental data. A kinetic-controlled growth model is also developed considering surface kinetics. Furthermore, an anisotropic sublimation growth model is proposed for the first time, in which aluminium vapour or nitrogen dominated model is applied along the c-axis and the kinetic model is employed perpendicular to the c-axis. The model is used to predict the transition temperature at which the morphology of the crystal changes. [ABSTRACT FROM AUTHOR]