The Studies On The Transport Behaviors And The Controlling Methods Of Oxide Semiconductor Nanowires Schottky Barriers

In this paper, we mainly studied the effects of surface states and barrier geometry on the transport behavior of the oxide semiconductor nanowires Schottky barriers, and investigated some methods to control the transport behavior of the Schottky barriers by controlling the surface states and barrier geometry. On the basis of these researches, some novel electronic and optoelectronic devices were developed.In the chapter 1, we introduced the background and the existing problem on the transport behavior of semiconductor naniwire Schottky barriers.In the chapter 2, we mainly studied the effects of surface states and barrier geometry on the transport behavior of CuO and ZnO nanowire Schottky barriers. The conductive atomic force microscopy was used to study the current image of a single CuO nanowire, and a surface states imaging method was developed. For the CuO nanowire back-to-back Schottky barriers structure, it was found that the rectifying behavior was caused by the asymmetric contact length, which can be well explained by the two-dimensional partly depleted Schottky barrier geometry model and the transmission line model. In addition, the photocurrent properties of a single ZnO nanowire Schottky photodiode showed unsaturated property, which can also be well explained by the two-dimensional partly depleted Schottky barrier geometry model. Under this barrier geometry model, the photocurrent equation of the ZnO nanowire was obtained, which was in good agreement with the experimental results.In the chapter 3, according to the effect of surface states and barrier geometry on the transport behavior of nanowire Schottky barriers, we investigated four methods to control the transport behavior of the nanowire Schottky barriers. Firstly, we used the electron beam lithography method to construct the three Schottky barrier structures, and investigated the effect of one Schottky barrier on the transport behavior of the other Schottky barriers. While, due to the effect of existing organic contaminations on the surface states and transport behavior of nanowire Schottky barriers, we did not obtain the expected results. Secondly, the atomic force microscopy lithography method was used to construct nanostructure on Pt/Cu bilayer electrode, which can effectively passivate the dangling bonds in the Cu-CuxO heterostructure. Thirdly, the electrodepositon and annealing method was used to deposite Cu on CuO nanowire, which can effectively passivate the dangling bonds and decrease the barrier height in the CuO nanowire Schottky barriers about 120 mV. Fourthly, local illumination method was used to illumnate the two Schottky barriers in the CuO nanowire back-to-back Schottky barriers structure respectively, which can not only increase the rectifying ratio, but also decrease the rectifying behavior and change the rectifying directions.In the chapter 4, we studied the electrical switching behavior of the ZnO nanowire back-to-back Schottky barrier structure, in which the positive current and negative current showed independent switching behavior. At +1.5 V bias, the on/off ratio of the positive current was about 105, and at -1.5 V bias, the on/off ratio of the negative current was about 103. The switching behavior of positive and negative current were caused by the barrier height change of right barrier and left barrier respectively, which were possibly caused by the adsorption and desorption of O2 on the surface of ZnO nanowire. Based on this switching behavior, two new-type ZnO nanowire Schottky barrier devices, the two-directional controlled Schottky barrier rectifier and the tristable memory, were developed. The two-directional controlled Schottky barrier rectifier can exhibit the rectifying behavior of both right barrier rectifier and the left barrier rectifier. The rectifying directions of the two rectifiers were opposite, and the rectifying directions can be switched. The rectifying ratio, turn-on voltage and ideal factor of left barrier rectifier were 150, 0.77 V, and 1.33, respectively. The rectifying ratio, turn-on voltage and ideal factor of right barrier rectifier were 3800, -1.05 V, and 1.41, respectively. The tristalbe memory was consisted of three electric memory states: the left barrier rectifying state, the right barrier rectifying state, and the linear state. The logic values of the three states can be obtained by reading the current value of the three states. And the triggered pulse can be used to switch the states among the three states.In the chapter 5, we made a conclusion of the researches of this paper, and expected the future investigations on the semiconductor nanowire Schottky barriers.