Study On Mechanism Of Pulsed Laser Deposition Of ZnO Film

ZnO, a direct large band gap semiconductor material, is a kind of important applicable electron-photonic and piezoelectric material with well electron-photonic prosperity. In various preparation methods, Pulse laser deposition (PLD), with great rapid development in experiment, is reported as one of the best prepared methods. We have investigated the mechanism of pulsed laser deposition in theory to have a comprehensive grasp of process of interaction between laser and material and film deposition mechanism, which is very important to prepare high quality film and study on film physics.The first process of PLD is the interaction of laser and material, namely the meltdown and plasma in the material surface. The ablating model of a bulk target irradiated by a pulsed laser is set up. Using the heat flow equation, the appropriate boundary conditions and initial values, we investigate in detail the temperature distribution of target before the melting; Using the combination of precisely analytical method and integral-approximation method, through solving the heat flow equation, the temperature distribution of solid and liquid phases as functions of time and location are obtained. Consequently, the ablation of target ZnO is calculated.The second process is the directional isothermal and adiabatic expansion. Using the dynamic mode of plasma and hydromechanics, we combine the process of meltdown with pulse laser and plasma expansion to investigate the effect of the laser parameters (power and wavelength). The main innovations and conclusions of this thesis are following:(1) Based on energy balance, we get the melting distribution with time during the research of meltdown. Using sensible bound,initial conditions and the heat flow equation with heat generation term, we investigate in detail the temperature distribution of target before melting. With both the combination of analytical method and integral-approximation method, we solve the heat flow equation to obtain the change of temperature distribution of solid and liquid phases.(2) In expansion of the plasma, we adopt kinetic equations which reflect aeolotropism distribution of plasma, then give aeolotropism of plasma concentration which is spheroid according to those equations. The results from ablation stage are taken as initial factors to discuss the movement of particle in plasma in isothermal and adiabatic expansion stages. According to these evolution disciplines, we get numerical simulation calculation, and the results manifest that laser power and wavelength are distinctive to the film characters.(3) The effects of different laser power and wavelength on film characters are studied on the basis of computer simulation. The results :(1) The higher laser power density is, the worse the flatness is. Namely the lower laser power density can improve the flatness of film, but the lower laser power density is, the slower the velocity of film deposition is. So power density must be suitable. (2) Whatever the wavelength is, the film is not absolutely smooth. The longer the wavelength is, the worse the flatness is. So the short wavelength laser is good for smooth film.