Pulsed Laser Deposition And Epitaxial Growth Of Bi₄Ti₃O₁₂/ZnO Hetero Structure

Electronic information system becomes smaller, faster and lower power consumption, which makes electronics materials become thin films and composite multifunction, also makes electric devices become chip and multi-functional integrated. The integration of ferroelectric thin films and semiconductor thin films would provide new ideas and possibilities for the development of high-performance electronic devices and new functional devices. The exploration of study on the novel ferroelectric/semiconductor heterostructures is significant to science and application.This thesis is to explore the integrated growth of Bi4Ti3O12(BiT) based ferroelectric thin films with ZnO-based semiconductor thin film. The epitaxial integration of (100)-oriented BHT thin film with Al-doped ZnO(AZO) thin films and Co-doped ZnO(Zn1-xCoxO) diluted magnetic semiconductor films is using pulsed laser deposition. The main contents and conclusions of the thesis are as follows.In order to explore the growth conditions of Bi4Ti3O12thin films, the BiT and BHT films were deposited on Pt (111)Ti/SiO2/Si substrates by pulsed laser deposition. The effect of conditions on structure of the films was studied and the comparative study on orientation and properties between BiT and BHT thin films was made. It is indicated that higher depostion temperature, oxygen pressure and laser energy can promote the growth of the non-c-axis-oriented grains in BiT and BHT thin films. The BHT film showed a significant anisotropy of the ferroelectric polarization, and the spontaneous polarization remains along the a-axis. Ho doping greatly improved the leakage and fatigue of BiT thin films.In order to reach the integrated growth of epitaxial BHT/ZnO based heterostructure, epitaxial ZnO-based semiconductor thin films as the base layer are necessary. The epitaxial growth of AZO transparent conductive film and Zn1-xCoxO diluted magnetic semiconductor thin film were studied. The (001)-oriented AZO transparent conductive film and Zn1-xCoxO diluted magnetic semiconductor thin film were epitaxially grown on c-sapphire substrates. The result revealed that the oxygen pressure played a significant impact on the structure and properties of AZO films, and the average transmittance of film grown on13Pa oxygen pressure is more than94%, and whose resistivity is the lowest one, which can be used as the substate for epitaxial growth of BHT films. Epitaxial Zn1-xCoxO thin films deposited in a vacuum environment show room-temperature ferromagnetism, however, after oxygen annealing at high temperature the frerromagnetism disappears and paramagnetic is showing, which can be attributed to the signifacantly increasing of resistivity of Zn1-xCoxO thin films.Finally, the epitaxial (100)-oriented BHT thin film was integrated with the epitaxial (001)-oiented AZO transparent conductive thin film and Zn1-xCoxO diluted magnetic semiconductor thin film. The (100) plane of BHT film has a long-range lattice matching relationship with the (001) plane of ZnO based semiconductor film, the epitaxial relationship in plane is BHT[100]//ZnO<010>. A preliminary exploration of the performance of the BHT/ZnO based semiconductor heterostrecture reveals that BHT(100)/AZO(001) heterostructure shows a transparent feature and the average transmittance of (500nm)BHT/(300nm)AZO heterostructure is higher than89%in the visible wavelength range. Both of the two heterostructure show ferroelectric characteristics and the ramenant polarization of BHT/AZO heterostructure is2.0μC/cm2. The BHT(100)/Zn1-xCoxO(001) heterostructure shows paramagnetic at room temperature.