Kinetic Monte Carlo Simulation Of Deposition Of Perovskite Ferroelectric Thin Film By Pulsed Laser Deposition

Current interest in ferroelectric thin film results from the potential applications in microelectronics, micro electromechanical system (MEMS) and information storing. Perovskite ferroelectric thin films have attracted much attention for the excellent piezoelectric, ferroelectric and pyroelectric properties. Pulsed laser deposition (PLD) is a conventional growth technique used for the growth of complex muticomponent thin films because of the ability to preserve the target stoichiometry. There are a lot of reports on PLD growth of perovskite ferroelectric thin film, but the initial growth stage has rarely been studied. The three-dimensional growth mechanism of perovskite ferroelectric thin film under a given condition is still controversial, and the effects of various experimental parameters also need to be further understood. Kinetic Monte Carlo (KMC) method could provide atomic-scale point of views on the growth of thin films, and was usually used to simulate the growth of metal and semiconducting thin films. However, few simulations were performed on the perovskite ferroelectric thin films because of the complexities of lattice structure and growth mechanism. In this thesis, a two-dimensional and a three -dimensional KMC models are developed to simulate the submonolayer and three-dimensional growths of perovskite ferroelectric thin film via PLD, respectively. Taking BaTiO3 thin film for example, we investigate the effects of various experimental parameters on PLD growth of perovskite ferroelectric thin film. The main contents are given as follows.Based on the traditional energy-dependent KMC models, we developed a two-dimensional KMC model to consider not only deposition of atoms and surface diffusion of adatoms but also bonding of adatoms according to perovskite structure. Born-Mayer-Huggins (BMH) potential is introduced to calculate the interactions between adatoms, and the bonding ratio is defined to reflect the crystinity of thin film. The effects of substrate temperature, laser pulse repetition rate and incident kinetic energy on the growth of BaTiO3 thin film at the submonolayer regime were investigated. The results show that the island density decreases with substrate temperature, laser pulse repetition rate and incident kinetic energy. The bonding ratio of atoms is enhanced by the increase of substrate temperature at the range of T >700 K, laser pulse repetition rate, and incident kinetic energy at the range of E K<9.6 eV. The substrate temperature hardly influences the growth of BaTiO3 thin film when T <700 K.A three-dimensional KMC model, including the deposition, diffusion and bonding of atoms, is developed to simulate the three-dimensional growth of BaTiO3 thin film via PLD. The overhanging is permitted in the deposition and diffusion of atoms, and the atoms are bonded according to perovskite structure. Born-Mayer-Huggins (BMH) potential is introduced to calculate the interactions between adatoms. The adatoms have to overcome the Ehrilich -Schwoebel (ES) potential when they diffuse to subjacent atomic layers. We investigated the effects of incident kinetic energy, laser pulse repetition rate and mean deposition rate on the three-dimensional growth mode and surface roughness of BaTiO3 thin film. Our results show that the saturated coverage of each atomic layer is about 0.75. The growth mode of BaTiO3 thin film transforms from island growth mode to layer-then-island growth mode with the increase of incident kinetic energy and decrease of laser pulse repetition rate, and the surface roughness decreases accordingly. BaTiO3 thin film grows in layer-then-island growth mode at Fa ver=1.0 ML/s and 0.1 ML/s. It grows in island growth mode at Fa ver=0.5 ML/s, and the surface roughness is larger than the former two.The effects of substrate temperature and incident kinetic energy on bonding ratio are in agreement with the experimental results of Roemer et al. and Duan et al. respectively, and the effect of laser pulse repetition rate on surface roughness is in agreement with the experimental results of Kim et al. This indicates the validity of our models. Our simulations provide better understanding of PLD growth of perovskite ferroelectric thin films and theoretical guideline for the materials design of perovskite ferroelectric thin film.