Zno Nanocrystalline Films Of The Structure, Luminescence And Doping

Electron cyclotron resonance plasma assisted pulsed laser deposition (ECR-PLD), is a novel method for film preparation. The regime of ECR-PLD is that the pulsed laser ablation (PLA) plasma and the electron cyclotron resonance (ECR) plasma interact and through which the target film is deposited on the substrate. This technique synthesizes the advantages of both PLD and ECR plasma. Moreover, it affords extra energy to the precursors so that they can migrate on the surface of the depositing film and take positions where their potential energy are lower, hence the films'quality could be improved. Considering this, the method is particularly suitable for film deposition at low temperature. The subject mainly investigated in this thesis is the application of ECR-PLD to ZnO thin film preparation.By means of ECR-PLD, we ablated a high purity metallic zinc target by a second harmonic ns Nd:YAG laser in the environment of the ECR oxygen plasma, and finally prepared high quality nanocrystalline ZnO film. We also applied many testing methods to the analysis and characterization of morphological, structural and optical properties. Atomic force microscopy shows the as-deposited ZnO films exhibit a smooth surface appearance, the cross-sectional view carried out by scanning electron microscope indicates the film thickness after deposition for 60 minutes is about 0.50um. Raman and Fourier transform Infrared spectroscopy confirm the wurtzite structure of ZnO. X-ray diffraction indicates that the growth of ZnO is along the (002) orientation. By fitting the absorption edge of the transmittance spectra in the ultraviolet region, the forbidden bandwidth of our ZnO film was calculated to be about 3.31eV. Spectral test of photo luminescence shows our ZnO thin films exhibit high intensity luminescence when excited by a 325nm UV laser, and the photoluminescence spectra are near-band-edge (NBE) emission rather than deep level emission (DLE).Based on the success of ZnO thin film deposition, we compared the differences of structural and optical properties of ZnO films annealed at different temperature, to investigate the optimal post treatment condition of the ZnO films. The results indicate that the optimal annealing temperature for ZnO thin film prepared by ECR-PLD is around 600℃.Besides silicon, fused silica and sapphire are another two kinds of frequently used substrates in the thin film preparation. Besides, fused silica is the most commonly used dielectric material and sapphire is a very promising high-k dielectric material. Therefore, the combination of these materials and ZnO thin films is worth to study. We found that ZnO films deposited on fused silica and sapphire are similar in principle with that on silicon, but there are still some differences, which tend to be more obvious for those post-annealed ZnO films. The lattice mismatch and thermal mismatch and the resulting strain force between ZnO films and substrates are probably responsible for those differences.We also did some preliminary research on doping during ZnO deposition process performed by ECR-PLD. Mixture gas composed of Oxygen and Nitrogen discharged by ECR is used instead of pure oxygen to achieve the N-doping in the ZnO thin films. ECR discharge make the gas molecular ionized and increase their reactivity in the film preparation, thereby offering the advantageous conditions to N-doping in the ZnO film. The N-doped ZnO films have much weaker photoluminescence than those undoped ones, however they could be improved after thermal annealing.To summarize, in this thesis we presented ZnO thin film preparation by ECR-PLD, and then analyzed and characterized ZnO thin films by many kinds of testing methods. The influences of annealing and substrates on the properties of ZnO thin films are also investigated, based on which, we discussed the growth mechanisms of ZnO thin films. During the recent more than ten years, studying on ZnO has been a hotspot of semiconductor research, and we hope our work may make some contribution to the extensive application in the future.