Adsorption and desorption kinetics of Ga on GaN(0001): Application of Wolkenstein theory

The kinetics of Ga adsorption/desorption on GaN (0001) surfaces is investigated over the temperature range of 680-750 degrees C using real-time spectroscopic ellipsometry. The adsorption and desorption kinetics are described in the framework of the Wolkenstein theory, which considers not only the equilibrium between Ga adsorbed on the surface and Ga in the gas phase but also the electronic equilibrium at the surface. It is shown that, because of the fixed polarization charge existing at the GaN(0001) surface, Ga adsorption and desorption processes involve neutral and charged Ga states. By considering the GaN surface charge involved in the surface processes, we demonstrate that a second-order kinetics more accurately describes Ga desorption, in comparison with conventional models, and yields an apparent activation energy of 2.85 +/- 0.02 eV for Ga desorption consistent with experiments.