Modelling of molecular beam epitaxy thin film growth with void defect formation

Molecular beam epitaxy (MBE) thin film growth is widely studied due to its applications in semiconductor devices technology. In this work, we use two discrete models to study the MBE growth in which void defect can be formed. These discrete models are Random Deposition (RD) model with thermal activation and Ballistic Deposition (BD) model with thermal activation. In the RD model with thermal activation, the deposition rule obeys Solid-On-Solid (SOS) condition: bulk vacancy, overhanging of an atom and desorption are not permitted. In the BD model with thermal activation, the SOS condition is not restricted in the deposition process. The diffusion process in which surface atoms can diffuse continuously without the SOS condition is possible in both models. From these models, we found that the substrate temperature has strong effect on morphology, void defect density and roughness of the film. In the RD model with thermal activation, the growth can be divided into two regimes. In the first regime, the temperature is low so the surface atom has low probability to diffuse. As a result, the film is very rough and the void defect density increases with the temperature. The roughness increases rapidly. In the second regime, at higher temperature, the film becomes smooth and the void defect density decreases as the temperature increases. The roughness increases slowly. In the BD model with thermal activation, when the substrate temperature increases, the film becomes smooth and the void defect density decreases while the roughness increases slower.