【作者】 张海峰；

【导师】 阮圣平；

【作者基本信息】 吉林大学 ， 物理电子学， 2012， 博士

【摘要】 本论文的主要工作为Ti_xZr_1-xO₂固溶体纳米薄膜和Ti_xZr_1-xO₂固溶体纳米线阵列的制备，并以不同形貌的Ti_xZr_1-xO₂纳米材料为基体材料制作了高性能紫外探测器。同时，对制作的紫外探测器的载流子输运机制、金半接触肖特基势垒高度及器件内部增益情况进行了详细的理论分析，取得了以下创新性结果：首先，采用溶胶凝胶法制备了不同Zr和Ti配比的Ti_xZr_1-xO₂固溶体纳米薄膜，并利用XRD，UV-visble，AFM，SEM，XPS等手段对各个薄膜进行了表征。实验发现Zr的掺入不但改善了纯TiO₂和纯ZrO₂纳米薄膜的表面龟裂情况，还使Ti_xZr_1-xO₂纳米薄膜的紫外吸收边发生了不同程度的蓝移，说明Zr的加入改变了复合材料的禁带宽度，为响应范围可调的紫外探测器的制备创造了条件。其次，以不同Zr和Ti配比的Ti_xZr_1-xO₂纳米薄膜为基体材料制作了高性能的MSM型紫外探测器。实验发现，掺入少量的Zr可以大大提高器件的响应度，然而掺入多量的Zr时，器件的响应度虽然会下降，但是器件的响应范围会发生明显的蓝移，根据这一特点，有望制作深紫外日盲型紫外探测器。另外，实验讨论了不同金属电极、不同器件结构对器件性能的影响，并从理论上分析了MSM结构器件载流子的输运机制。同时，本论文首次提出了三极管模型解释MSM结构紫外探测器的增益机制。再次，为了优化基体材料结构，实验采用低温极性水解法直接在FTO透明导电玻璃上制备了Ti_xZr_1-xO₂固溶体纳米线阵列，并采用XRD，SEM， XPS等方式对材料进行了表征，证明了本实验制备的材料为长度4μm、直径20nm、垂直衬底生长的Ti_xZr_1-xO₂纳米线阵列。同时，本文对Ti_xZr_1-xO₂纳米线的生长机制、生长速度及纳米线直径的控制等方面提出了相应的理论模型，为Ti_xZr_1-xO₂纳米线基体在后续电子器件制作、相应半导体工艺研究及载流子输运机制的分析中打好基础。最后，本论文首次以Ti_xZr_1-xO₂固溶体纳米线阵列为基体材料制备了Ag电极的单肖特基结紫外探测器，通过纳米线对少子的限域作用来减少载流子的复合，并对电子提供一维传输的导向作用，在基体材料上优化了器件性能。同时，本文通过三种方法详细计算了Ag/Ti_xZr_1-xO₂接触的肖特基势垒高度，并对器件的载流子传输机制及内部增益情况进行了理论分析。更多还原

【Abstract】 Sensor, as the interface between system monitoring and research object, plays animportant role in obtaining information. Ultraviolet detector as an important branch oftraditional sensors, has attracted a great deal of interests in civil and military applications.Due to the smaller volume, higher efficiency, lower power dissipation and cost, wide bandgap semiconductors based Ultraviolet detectors have become the mainstream. Studies onthe substrate materials of UV detector were mainly concentrated on GaN and SiC duringthe past years, and extended to some metal oxide, such as ZnO, TiO2in recent years.However, the binary wide-band gap materials have their own limitations, the responsivitystill needs to be improved and the detection range could be extended further. To date, a lotof attention has been paid to the complex oxide materials, such as ZnxMg1-xO, Zn2GeO4and Zr_xTi_1-xO₂due to their improved physical and chemical properties and the tunable bandgap.Zr_xTi_1-xO₂exhibits similar material advantages as pure TiO2and offers a way ofobtaining titania with higher surface area and better thermal stability. In addition, the bandgap of Zr_xTi_1-xO₂can be tuned from3.2eV （TiO2） to7.8eV （ZrO2） by varying the Zrcomposition. Therefore, it has much potential superiority in adjusting its UV absorptionedge and fabricating solar blind UV detector.In this letter, Zr_xTi_1-xO₂nano films were prepared by a sol-gel method and characterizedby means of XRD, SEM, XPS, AFM and UV-visible absorption spectra. The XRD patternsshow that Zr_xTi_1-xO₂solid solution was formed when a few Zr was doped; SEM imagesshow that there was serious crack appear on pure TiO2sample and ZrO2sample surface,and the combination of TiO2and ZrO2would improve the surface smoothness of the film; the UV-visible absorption spectra of Zr_xTi_1-xO₂films shows that the doping of Zr increasesthe UV absorption edge and the band gap of Zr_xTi_1-xO₂; The ratio between Zr and Ti on thefilm surface was semi-quantitatively estimated by XPS spectra, it is found that Zr waseasier react with oxygen due to its lower electronegativity.Based on Zr_xTi_1-xO₂thin films, MSM structure UV electrodes were designed, and the I-Vcharacteristics and the responsivity of the devices were measured. For the Zr_xTi_1-xO₂detectors with lower Zr doping, higher photoresponse was obtained than that of TiO2,which can be explained by the introduction of Zr atom. It is well known that theelectronegativity of zirconium atom is weaker than that of titanium atom. As theisoelectronic impurities of Ti, Zr in the lattice could be treated as hole traps, and thusfurther results in the reduction of Schottky barrier. That is, higher responsivity is obtained.However with further increasing of Zr, the response peaks shift to shorter wavelengthdirection and the photoresponses drop significantly. This is because that the introduction ofZr could not only increase the resistance of the neutral region between electrodes, but alsodecrease the absorption coefficient of Zr_xTi_1-xO₂films. However, the responsivity could beimproved by optimizing the film quality and the distance between electrodes. So thefabricating of high response solar blind UV detector is quite possible.High responsivity metal-semiconductor-metal Zr_xTi_1-xO₂ultraviolet photodetectors withNi, Pt and Au electrodes were identically fabricated to explore the influence of metalelectrodes on device performance. It has been confirmed that when Ni is deposited on topof the Zr_xTi_1-xO₂film, the work function of Ni will decrease. It may be because that theelectron would transfer from Ni to the substrate, which will form a dipole layer between Niand Zr_xTi_1-xO₂, and result in the decrease of SBH, therefore high responsivity was obtained.For the Pt electrodes, it produces the highest Schottky barrier and low Schottky barriercapacitance, so fast recover time was obtained. In addition, different device structures werealso studied to explore the influence on the performance of ultraviolet detectors. Thesandwich structure UV detector fabricated by adding an additional Zr_xTi_1-xO₂lay on theoriginal MSM UV detector, achieves higher responsivity and long-term stability because ofthe three-dimensional structure of back-to-back Schottky junction and the protective effect of metal electrode from corrosion by air, water vapor.The carrier transport mechanism and its gain mechanism for MSM devices were alsoanalyzed in detail. For the significant gain of Zr_xTi_1-xO₂based detector with Au electrodes（967）, the traditional theory was difficult to explain such a high gain. Therefore,phototransistor model was firstly proposed in this paper.The Zr_xTi_1-xO₂nanowire array was prepared via a low-temperature hydrothermal methodand characterized by means of XRD, SEM, and XPS. One-dimensional Zr_xTi_1-xO₂nanowire could decrease the recombination probability of photogenerated electron-hole andlargely increase the photoresponse owing to the fact that the photogenerated holes may betrapped in the surface states of Zr_xTi_1-xO₂nanowire caused by the adsorbed O2. In addition,well-aligned Zr_xTi_1-xO₂NWS arrays have been demonstrated with fast electron transportand straight conduction pathways, which are beneficial in obtaining a faster response time.The diameter and length of the nanowire were20nm and4μm, respectively. For thegrowth mechanism of nanowires, growth unit model and over-saturation growth modelwere proposed to analyze the growth rate and growth mechanism. In addition, thecontrolled growth of the nanowire diameter was also analyzed in detail.Based on the Zr_xTi_1-xO₂nanowire array, Schottky photodiode UV detectors with Agelectrodes were fabricated. Back-side illumination was adopted to increase the lightabsorption effectively. In addition, the Zr_xTi_1-xO₂/Metal Schottky contact characteristicswas researched in detail and the barrier height value was calculated, this Schottky diodedetector with simple fabrication process, low cost and superior performance wouldprovides a new way in fabricating UV imaging arrays. The Schottky barrier height of thedevice was analyzed by theoretical calculations, the thermionic emission theory and theXPS spectra analysis, it is found that the work-function of Ag increased considerably due tothe oxygen adsorbed on Ag, which could greatly increased the Schottky barrier heightbetween Ag and Zr_xTi_1-xO₂. In addition, the Schottky photodiode UV detector also obtainedinternal gain, which may be induced by the reduction of the Schottky barrier at Ag/TiO2interface under illumination.更多还原