Pulsed Laser Deposition And Photoelectric Characteristics Of SrTiO₃/Nb:SrTiO₃ Heterojunctions

Fabrication of high quality and multifunction thin films and devices plays an important role in the development of integrated optics and photoelectric technology. Pulsed laser deposition (PLD) is one of the most advanced methods for film growth. In this thesis, SrTiO₃ films and its heterostructures SrTiO₃/Nb:SrTiO₃ have been fabricated using PLD method and the electrical and photoelectrical characteristics of the junctions have been investigated.The fundamental physics involving laser-material interaction and laser-plasma interaction during PLD process has been studied thoroughly. The impacts of deposition parameters such as the pulse energy density, the laser pulse frequency, the oxygen pressure, the substrate temperature and the substrate species on film growth have been investigated systematically.SrTiO₃ thin films were deposited on Nb: SrTiO₃ substrates with different Nb doping levels using PLD method. Optimized deposition parameters were employed to achieve smooth epitaxial films with high crystalline perfection. X-ray diffractometer (XRD), transmission electron microscope (TEM) and confocal Raman micro-spectroscopy were used for the microstructure analysis. The characteristics of SrTiO₃/Nb:SrTiO₃ heterojunctions were found to be modulated by the Nb doping levels of substrates.The electrical transport and photoelectrical properties of SrTiO₃/Nb:SrTiO₃ heterojunctions have been investigated. The hysteretic current-voltage curves, remarkable resistance switching phenomena and multi-resistance states were observed and the results have been discussed by considering the role of defects in the interfacial depletion region of the heterojunctions. The photoconductivity and photovoltaic effects of SrTiO₃/Nb:SrTiO₃ heterojunctions under ultraviolet light irradiation have been measured. These behaviors depend on the Nb doping levels of substrates and the junction with higher Nb concentration in the substrate shows larger photoconductivity. Furthermore, photovoltaic effects in the junction with multi-resistance states have been found to correlate with its resistance states. In the junction with high Nb doping level, defects with high concentration create a considerable number of defect energy levels, which act as "traps" of electrons, in the electrical band structure of interface. When external electrical field or light are applied, trapping or detrapping of electrons by these defects result in the resistance switching, multi-resistance states and particular photovoltaic phenomena. This work is helpful for understanding fundamental physics of light-matter interaction and is useful for fabrication of novel photoelectric devices.