Thermodynamic and kinetic processes involved in the growth of epitaxial GaN thin films

Our experimental results using reactive magnetron sputtering, combined with earlier literature, are used to understand the thermodynamic and kinetic processes involved in GaN film growth and the limiting factors involved in the incorporation of nitrogen during the growth process. We show that GaN films fabricated with low pressure growth techniques (<0.1 Torr) such as sputtering and molecular beam epitaxy are formed under metastable conditions with a nonequilibrium kinetically limited reaction. For these methods, the growth process is controlled by a competition between the forward reaction, which depends on the arrival of activated nitrogen species at the growing surface, and the reverse reaction whose rate is limited by the unusually large kinetic barrier of decomposition of GaN. In practice, the thermally activated rate of decomposition sets an upper bound to the growth temperature.