The Growth Of Epitaxial Ba Ti O3 / Zn O Heterojunction And Electrical Properties

The rapid development of information technology in the world cannot leave the nonvolatile memory continuously improve performance. In order to obtain excellent performance of new type memory, a large number of researchers are looking for a substitute for conventional memory. In this research area, we found variety of oxide material have resistance switch phenomenon,most of the material have the potential applications for nonvolatile memory. Most of the traditional mechanism of nonvolatile memory can be divided into two categories, one kind is ion mechanism, the other is electronic mechanism, compared with the ion mechanism, the electronic mechanism usually to explain the resistance switch. However, the defect is closely related to resistive switching and difficult to control. Thus the conventional resistive switching memory has not got a great success in the commercialization. Ferroelectric/semiconductor heterojunction is always the hot device application, it features by the interfacial effect and the photonic band gap is adjustable, so the structure design and research has become a new bright spot. Heterostructures composed of semiconductor materials with spontaneous lattice polarizations bear exciting opportunities for employment of ferroelectric state variables as additional degree of freedom for device applications. Ferroelectric/semiconductor heterojunction as resistive switching device has been found to show a large switching ratio in recent years, since the barrier height and width are adjustable at the same time. A broad category of materials and structures have been found to be used as memristors, and a typical memristor is constructed from either capacitorlike or planar metal-oxide-metal(MIM) structures. ZnO is a kind of typical semiconductor, and BaTiO3 lattice mismatch between the smaller, less than 2 %, so BaTi O3/ZnO epitaxial heterojunction should be easily obtained. In this paper, BaTiO3/ZnO epitaxial heterojunction was grown by pulsed laser deposition(PLD).In this paper, we first used of four different orientations(ACMR) sapphire substrates were prepared by different orientation of epitaxial ZnO thin films, and further characterization of their properties. Then we explored by pulsed laser deposition conditions of preparation of epitaxial BaTiO3/ZnO heterojunction, through the sample preparation we found in the polarity of the ZnO thin film on the easy formation of epitaxial BaTiO3/ZnO heterojunction, but in nonpolar ZnO thin film preparation is difficult. We grow in the samples of electrode by the sputtering process for electrical measurement, and the structure is Au/Ba TiO3/(Au) ZnO/sapphire(ACMR). After the I-V scanning of devices to make use of Keithley 2400, found with the same conditions on the different substrate preparation device of the I-V characteristics are different, we use schottky thermionic emission model respectively to fit their IV curve to calculate the effective barrier height, barrier height difference is what leads to the phenomenon of different reasons. And we also found in the same substrate(a-plane sapphire) with different laser energy of the preparation of the sample voltage and current response are also different, rectification effect was observed for the system grown in high energy, while bipolar resistive switching was exhibited for those grown in low energy. By the samples of C-V test and theory of interface states, our samples interface type belongs to the donor-like interface state, belong to the positive charge interface defects. The calculation of surface state density of samples, we found that the surface state density is smaller for the sample grown at a higher laser energy, and the barrier height increases while the surface state density reduces. We used the Fermi energy level pinning effect and charge transfer theory to explain the reasons of this phenomenon occurs, and expounds the BaTiO3/ZnO heterojunction asymmetric rectifier feature. Under the low temperature of the samples, we also to the electrical test, found our samples of electrical performance is indeed can test temperature changing, by calculating the ideal factor changes.