氧化物半导体纳米线肖特基势垒的传输特性及其控制方法研究
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摘要
在本论文的研究中,我们研究了表面态和势垒结构对CuO、ZnO等氧化物半导体纳米线肖特基势垒输运特性的影响,基于对表面态和势垒结构的调控,探索了几种对纳米线肖特基势垒输运特性进行调控的方法。在此基础上,发展了几种基于纳米线肖特基势垒的新型光电功能器件。
在研究表面态对CuO纳米线肖特基势垒输运的影响时,我们发现了表面态在纳米线表面的条状分布特性,并发展了一种对纳米线表面态进行空间分布成像的方法。另外,我们提出了部分耗尽的肖特基势垒二维结构模型,利用该模型,对CuO纳米线背靠背肖特基势垒结构中与接触长度比有关的整流特性,以及ZnO纳米线肖特基势垒光电二极管的不饱和光电流特性进行了解释。
我们探索和发展了多种对势垒的输运特性进行调控的方法:构筑了三肖特基势垒结构,研究了该结构中势垒间输运特性的相互影响;发展了AFM刻蚀和电沉积结合烧结等两种钝化悬空键的有效方法;提出了一种利用局域光照对纳米线背靠背结构中的两个势垒分别进行控制的方法。另外,在ZnO纳米线背靠背肖特基势垒结构中,在电学脉冲的控制下,可以对两个势垒的势垒高度分别进行控制,使正负电流表现出独立的开关特性,以此为基础,发展了双向可控肖特基势垒整流器和三稳态存储器等新原理性器件。
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.
在研究表面态对CuO纳米线肖特基势垒输运的影响时,我们发现了表面态在纳米线表面的条状分布特性,并发展了一种对纳米线表面态进行空间分布成像的方法。另外,我们提出了部分耗尽的肖特基势垒二维结构模型,利用该模型,对CuO纳米线背靠背肖特基势垒结构中与接触长度比有关的整流特性,以及ZnO纳米线肖特基势垒光电二极管的不饱和光电流特性进行了解释。
我们探索和发展了多种对势垒的输运特性进行调控的方法:构筑了三肖特基势垒结构,研究了该结构中势垒间输运特性的相互影响;发展了AFM刻蚀和电沉积结合烧结等两种钝化悬空键的有效方法;提出了一种利用局域光照对纳米线背靠背结构中的两个势垒分别进行控制的方法。另外,在ZnO纳米线背靠背肖特基势垒结构中,在电学脉冲的控制下,可以对两个势垒的势垒高度分别进行控制,使正负电流表现出独立的开关特性,以此为基础,发展了双向可控肖特基势垒整流器和三稳态存储器等新原理性器件。
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.
引文
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[3]JU S, LEE K, JANES D B. Low operating voltage single ZnO nanowire field-effect transistors enabled by self-assembled organic gate nanodielectrics [J]. Nano Lett., 2005, 5: 2281-2286.
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[9]SOCI C, ZHANG A, XIANG B, et al. ZnO nanowire UV photodetectors with high internal gain [J]. Nano Lett., 2007, 7: 1003-1009.
[10]LI Q H, WAN Q, LIANG Y X, et al. Electronic transport through individual ZnO nanowires [J]. Appl. Phys. Lett., 2004, 84: 4556-4558.
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[15]LI H J, LU W G, LI J J, et al. Multichannel ballistic transport in multiwall carbon nanotubes [J]. Phys. Rev. Lett., 2005, 95: 086601.
[16]MANOHARA H M, WONG E W, SCHLECHT E, et al. Carbon nanotube Schottky diodes using Ti-Schottky and Pt-Ohmic contacts for high frequency applications [J]. Nano Lett., 2005, 5: 1469-1474.
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[18]HEO Y W, TIEN L C, NORTON D P, et al. Pt/ZnO nanowire Schottky diodes [J]. Appl. Phys. Lett., 2004, 85: 3107-3109.
[19]KIM J R, OH H, SO H M, et al. Rectifying diode made of individual gallium nitride nanowire [J]. Phys. E, 2003, 18: 225-226.
[20]MARTEL R, DERYCKE V, LAVOIE C, et al. Ambipolar electrical transport in semiconducting single-wall carbon nanotubes [J]. Phys. Rev. Lett., 2001, 87: 256805.
[21]HEINZE S, TERSOFF J, MARTEL R, et al. Carbon nanotubes as Schottky barrier transistors [J]. Phys. Rev. Lett., 2002, 89: 106801.
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[23]PARK W I, YI G C, KIM J W, et al. Schottky nanocontacts on ZnO nanorodarrays [J]. Appl. Phys. Lett., 2003, 82: 4358-4360.
[24]CHENG K, CHENG G, WHANG S J, et al. Surface states dominative Au Schottky contact on vertical aligned ZnO nanorod arrays synthesized by low-temperature growth [J]. New J. Phys., 2007, 9: 214.
[25]NAM C Y, THAM D, FISCHER J E. Disorder effects in focused-ion-beam deposited Pt contacts on GaN nanowires [J]. Nano Lett., 2005, 5: 2029-2033.
[26]ZHANG Z Y, JIN C H, LIANG X L, et al. Current-voltage characteristics and parameter retrieval of semiconducting nanowires [J]. Appl. Phys. Lett., 2006, 88: 073102.
[27]LONG Y, CHEN Z, WANG W, et al. Electrical conductivity of single CdS nanowire synthesized by aqueous chemical growth [J]. Appl. Phys. Lett., 2005, 86: 153102.
[28]LAO C S, LIU J, GAO P, et al. ZnO nanobelt/nanowire Schottky diodes formed by dielectrophoresis alignment across Au electrodes [J]. Nano Lett., 2006, 6: 263-266.
[29]HARNACK O, PACHOLSKE C, WELLER H, et al. Rectifying behavior of electrically aligned ZnO nanorods [J]. Nano Lett., 2003, 3: 1097-1101.
[30] Shalish I, Temkin H, Narayanamurti V. Size-dependent surface luminescence in ZnO nanowires [J]. Phys. Rev. B, 2004, 69: 24540.
[31]PAN Z W, DAI Z R, WANG Z L, et al. Nanobelts of semiconducting oxides [J]. Science, 2001, 291: 1947-1949.
[32]JIANG X, HERRICKS T, XIA Y. CuO nanowires can be synthesized by heating copper substrates in air [J]. Nano Lett., 2002, 2: 1333-1338.
[33]DU G H, TENDELOO G V. Cu(OH)2 nanowires, CuO nanowires and CuO nanobelts [J]. Chem. Phys. Lett., 2004, 393: 64-69.
[34]CHING W Y, XU Y N, WONG K W. Ground-state and optical properties of Cu2O and CuO crystal [J]. Phys. Rev. B, 1989, 40: 7684-7695.
[35]MUSA A O, AKOMOLAFE T, CARTER M J. Production of cuprous oxide, a solar cell material, by thermal oxidation and a study of its physical and electrical properties [J]. Sol. Energ. Mat. Sol. C., 1998, 51: 305-316.
[36]MALKOVA N, NING C Z. Surface states of wurtzite semiconductor nanowires with identical lateral facets: a transfer-matrix approach [J]. Phys. Rev. B, 2006, 74: 155308.
[37]LEAO C R, FAZZIO A, DASILVA A J R. Si nanowires as sensors: choosing the right surface [J]. Nano Lett., 2007, 7: 1172-1177.
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