氧化镉基纳米结构薄膜的制备及应用性能研究

发布时间：2018-07-12 19:24

本文选题：脉冲激光沉积 + 磁控溅射　；参考：《吉林大学》2014年博士论文

【摘要】：氧化镉(CdO)是属于II-VI族的一种直接窄带隙n型半导体氧化物，在常温下具有立方NaCl晶体结构。CdO薄膜本身具有大量的本征点缺陷，如氧空位(Vo)和镉间隙原子(Cdi)等缺陷，它们作为浅施主为CdO提供了大量的载流子，使其具有较低的电阻率(10-3~10-4Ω cm)。CdO的禁带宽度(Eg)为2.2eV，对应的波长为550nm，位于太阳光谱在可见光波段能量最强值510nm附近。因此，CdO以其高载流子浓度、低电阻率、可见光区域高透过率等特点，被广泛的应用于透明电极、太阳能电池、光电晶体管和气敏传感器等领域。然而，CdO的禁带宽度过窄极大地限制了其在光电器件领域的应用。为了与其它TCOs薄膜竞争，在提高CdO的电学性能的同时，通过掺杂其它元素或调解工艺参数增加其禁带宽度来提高薄膜在可见光波段的透过率范围，改善其光学性能。本论文对CdO薄膜的光学、电学和气敏性等性质进行了系统的总结，详细介绍了CdO的各种实际应用和制备方法，同时对CdO薄膜的研究方向进行了展望。采用磁控溅射法和脉冲激光沉积技术制备CdO基薄膜，通过调节化学计量比或掺杂过渡元素、稀土元素(Gd、Ce、In)等途径来制备导电性好、可见光区域透过率高的透明CdO薄膜。在此基础上，将Gd和In掺杂的CdO薄膜沉积在p-Si上制备异质结太阳能薄膜电池并研究其电学性能，探究CdO基薄膜作为太阳能薄膜电池的可能性。使用单束飞秒激光技术在CdO薄膜表面诱导出周期纳米条纹结构，并将该微型结构薄膜制成CdO/p-Si异质结。我们希望这些研究能够拓展CdO纳米材料在光电器件和太阳能薄膜电池等领域的应用。利用X射线衍射仪(XRD)、X射线光电子能谱(XPS)、衍射透射电子显微镜(TEM)、高倍透射电子显微镜(HRTEM)、场发射扫描电子显微镜(FE-SEM)及场发射扫描电子显微镜配套的能谱仪(EDS)对薄膜的成分和微观组织进行了分析和观察；利用紫外-可见光分光光度计(UV-VIS)、霍尔效应仪(Hall)对薄膜的光学和电学性能进行了表征；采用电流-电压(I-V)伏安特性曲线对异质结的电学性能进行了表征。具体的实验内容和结果如下： 1.利用脉冲激光沉积法(PLD)在普通玻璃衬底上制备未掺杂CdO薄膜，氧气气氛压强为10Pa，衬底温度为室温(25℃)，靶材为纯度99.99%CdO粉末制备的陶瓷靶。研究了不同脉冲激光能量密度(10~25J/cm2)下获得的CdO薄膜的晶体结构、光学和电学性能影响。结果表明所有薄膜为多晶CdO立方晶体结构，沿着[200]方向高度择优生长。随着激光能量密度的下降，薄膜的平均晶粒尺寸变化较大，由108.3nm变为21.1nm。晶粒尺寸的不断减小使得薄膜应力增加并导致薄膜表面Cd和O原子扩散速率改变，薄膜内以氧空位(Vo)为主的缺陷逐渐增多，而这些缺陷能级使得本征CdO薄膜的自由电子浓度增加。拥有最小晶粒尺寸的CdO薄膜在可见光区域内具有高的光学透过率(~92%)，明显变宽的禁带宽度(3.33eV)，高的载流子浓度(1.25×1021cm-3)和低的电阻率(2.8×10-4cm)。使得该实验方法和工艺条件下制备的晶粒尺寸较小的CdO薄膜在太阳能电池、透明薄膜电极和其它光电子设备具有广泛的应用前景。 2.通过射频磁控溅射法(RFMS)在普通玻璃衬底上沉积了铈(Ce)和钆(Gd)共掺杂氧化镉透明导电薄膜。气体气氛总压强为10Pa，其中氩气(Ar)气体流量为40sccm，氧气(O2)气体流量为10sccm，衬底温度为400℃，靶材为纯度99.99%的CdO、CeO2和Gd2O3粉末充分混合制备的陶瓷靶。研究了不同Ce和Gd含量对CdO薄膜晶体结构、光学和电学性能的影响。Ce和Gd的掺杂促进所有薄膜沿[200]方向的择优生长，(200)晶面衍射角(θ)逐渐变小，晶格常数(a)逐渐变大。0.4at.%Ce和0.8at.%Gd掺杂的薄膜具有最佳的光电学性能，在可见光区域内具有高的光学透过率(~85%)，光学禁带宽度增大为2.99eV，电阻率达到最小值3.3×10-4Ω cm。当Ce和Gd的掺杂含量进一步增加到0.5at.%和1.0at.%时，晶界散射和电离杂质散射作用的增强导致薄膜的光学和电学性能下降。因而，适当的Ce和Gd掺杂能够改善CdO薄膜的光学和电学性能，使其在透明导电材料方面具有重要的应用价值。 3.通过脉冲激光法(PLD)在石英玻璃基底上沉积了钆(Gd)和铟(In)共掺杂氧化镉透明导电薄膜。氧气气氛压强为10Pa，衬底温度为200℃，靶材为纯度99.99%的CdO、In2O3和Gd2O3粉末充分混合制备的陶瓷靶。XRD分析证实所有薄膜具有立方NaCl晶体结构，具有高度(200)择优取向。而XPS分析表明In的掺杂导致了In2O3相的出现。随着Gd和In的掺杂含量的不断增加，薄膜的晶粒尺寸由40nm逐渐减小为23nm。所有薄膜在可见光范围内都有很高的透过率(~85%)。尤其是2at.%Gd和4at.%In掺杂的CdO薄膜在可见光波段的透过率高达92%，其相应的禁带宽度为3.56eV。在相同实验条件下，将这些薄膜沉积在p-Si衬底上制得p-n异质结。样品的I-V特性曲线表明实验制得的异质结具有二极管特性，而且在光照条件下表现出了明显的光伏效应。3at.%Gd和6at.%In掺杂的CdO薄膜表现出最佳的光伏特性。其光电转换效率达到了7.5%，填充因子为63%，饱和电流密度(Jsc)和开路电压(Voc)分别为11.4mA/cm2和1.04V。实验结果表明掺杂Gd和In的CdO薄膜在太阳能薄膜电池方面具备潜在应用价值。 4.利用脉冲激光沉积法(PLD)在普通玻璃衬底上制备未掺杂CdO薄膜，氧气气氛压强为10Pa，衬底温度为25℃。将制得的薄膜在马弗炉里进行退火处理，退火温度和退火时间分别为200℃和30min。使用单光束飞秒激光脉冲在CdO薄膜表面上采用不同的脉冲重复频率进行周期纳米条纹结构诱导。输出激光脉冲的中心波长为800nm，脉冲宽度为100fs，重复频率为1~2500Hz可调，，单脉冲能量为2mJ。由FE-SEM观察可知，经过2000个脉冲数照射后，CdO薄膜表面出现短周期条纹微型结构，条纹周期为150~170nm。当脉冲数大于2000时，CdO表面开始出现蓬松的纳米泡沫的微型结构。配套积分球的UV-VIS测试表明具有飞秒激光微型结构的CdO薄膜具有宽频高吸收的特性。而Hall效应测试表明，当脉冲数为2000时，CdO薄膜获得最高的载流子浓度为1.9×1021cm-3和最低电阻率为1.3×10-5Ωcm。在此基础上，利用飞秒激光微型结构薄膜来制备的CdO/p-Si异质结，在暗态和光照两种环境下均表现出良好的整流特性。光照条件I-V特性曲线表明异质结具有光伏特性，测得最佳的太阳能电池开路电压Voc为0.55V，短路电流Jsc为6.8mA/cm2，填充因子为29.1%，转换效率为1.1%。飞秒激光微型结构薄膜的宽频高吸收特性使其在很多的光电器件领域，如光伏器件、电荷藕合器件和光探测器等具有潜在的应用前景。
[Abstract]:Cadmium oxide (CdO) is a direct narrow band gap n type semiconductor oxide which belongs to the II-VI family. The.CdO thin film with cubic NaCl crystal structure at normal temperature has a large number of intrinsic point defects, such as oxygen vacancy (Vo) and cadmium gap atom (Cdi), which provide a large number of carriers for the shallow donor for CdO, and make it have a lower resistivity. The forbidden band width (Eg) of (10-3~10-4 Omega cm).CdO is 2.2eV and the corresponding wavelength is 550nm, located near the maximum energy value of the solar spectrum in the visible light band. Therefore, CdO is widely used in transparent electrodes, solar cells, phototransistors and gas sensitive transmission with its high carrier concentration, low resistivity and high transmittance in visible light region. However, the narrow band width of CdO restricts its application in the field of optoelectronic devices. In order to compete with other TCOs films, in order to improve the electrical properties of CdO, increase the band gap by doping other elements or mediation process parameters to improve the transmittance range of the thin film in the visible light band and improve its light. Learning performance.
In this paper, the properties of optical, electrical and gas sensitivity of CdO films are systematically summarized. Various practical applications and preparation methods of CdO are introduced in detail. At the same time, the research direction of CdO films is prospected. CdO based films are prepared by magnetron sputtering and pulsed laser deposition, by adjusting the stoichiometric ratio or doping transition element. Gd, Ce, In, etc. are used to prepare transparent CdO thin films with good conductivity and high transmittance in visible region. On this basis, Gd and In doped CdO films are deposited on p-Si to prepare heterojunction solar thin film batteries and their electrical properties are studied. The possibility of the CdO based thin film as a solar thin film battery is explored. Single beam flight is used. Second laser technology induces the periodic nanoscale stripe structure on the surface of the CdO film, and makes the microstructural thin film into CdO/p-Si heterojunction. We hope that these studies can expand the application of CdO nanomaterials in the fields of photoelectric devices and solar thin film batteries. Using X ray diffractometer (XRD), X ray photoelectron spectroscopy (XPS), diffraction transmission electricity The composition and microstructure of the films were analyzed and observed by TEM, HRTEM, field emission scanning electron microscopy (FE-SEM) and field emission scanning electron microscopy (EDS). The optical and electrical properties of the films were used by ultraviolet visible Photometer (UV-VIS) and Holzer effect instrument (Hall). The properties were characterized, and the electrical properties of the heterojunction were characterized by the current voltage (I-V) volt ampere characteristic curve. The specific experimental contents and results were as follows:
1. the amorphous CdO film was prepared by pulsed laser deposition (PLD) on the ordinary glass substrate. The oxygen atmosphere pressure was 10Pa, the substrate temperature was room temperature (25 C) and the target was prepared by the purity of 99.99%CdO powder. The crystal structure, optical and electrical properties of the CdO film obtained under different pulse laser energy density (10~25J/cm2) were studied. The results show that all the thin films are polycrystalline CdO cubic crystal structure, and the growth of the average grain size is higher along the [200] direction. With the decrease of the laser energy density, the average grain size of the thin film varies greatly. The decrease of the grain size from 108.3nm to the 21.1nm. grain size makes the film stress increase and lead to the change of the Cd and O atom diffusion rate on the surface of the film. The defects of the oxygen vacancy (Vo) in the film increase gradually, and these defect levels increase the free electron concentration of the intrinsic CdO film. The CdO thin films with the smallest grain size have high optical transmittance (~92%) in the visible region, the broadened band gap (3.33eV), high carrier concentration (1.25 x 1021cm-3) and low resistance. The rate (2.8 x 10-4cm) makes the CdO thin films with smaller grain size prepared under the experimental and technological conditions have a wide application prospect in solar cells, transparent thin film electrodes and other photoelectron devices.
2. Ce and gadolinium (Gd) Co doped transparent conductive film are deposited on ordinary glass substrates by RF magnetron sputtering (RFMS). The total pressure of gas atmosphere is 10Pa, in which the gas flow rate of argon (Ar) is 40sccm, oxygen (O2) gas flow is 10sccm, the substrate temperature is 400, the target is 99.99% CdO, CeO2 and Gd2O3 powder is fully mixed. The effects of the content of different Ce and Gd on the crystal structure, optical and electrical properties of CdO films are studied. The doping of.Ce and Gd promotes the preferred growth of all thin films along [200] direction. (200) the diffraction angle of the crystal (theta) becomes smaller and the lattice constant (a) gradually becomes larger in.0.4at.%Ce and 0.8at.%Gd doped films. It is possible to have high optical transmittance (~85%) in the visible light region, the width of optical band gap is increased to 2.99eV, the resistivity is 3.3 x 10-4 Omega cm., when the doping content of Ce and Gd is further increased to 0.5at.% and 1.0at.%, the enhancement of the grain boundary scattering and the enhancement of ionizing impurity scattering leads to the decrease of the optical and electrical properties of the film. The doping of Ce and Gd can improve the optical and electrical properties of CdO thin films, and make them have important application value in transparent conductive materials.
3. the transparent cadmium oxide film Co doped with gadolinium (Gd) and indium (In) was deposited on the quartz glass substrate by pulsed laser method (PLD). The oxygen atmosphere pressure was 10Pa, the substrate temperature was 200, the target material was 99.99% CdO, and the In2O3 and Gd2O3 powder fully mixed with the ceramic target.XRD confirmed that all the thin films had cubic NaCl crystal structure. The XPS analysis shows that the doping of In leads to the appearance of In2O3 phase. With the increase of the doping content of Gd and In, the grain size of the thin film gradually decreases from 40nm to the high transmittance (~85%) in the visible light range of all the 23nm. films (~85%), especially the CdO film doped with 2at.%Gd and 4at.%In in visible light. The transmittance of the band is up to 92%, and the corresponding band gap is 3.56eV. under the same experimental conditions. These films are deposited on the p-Si substrate to produce p-n heterojunction. The I-V characteristic curve of the sample shows that the experimental heterojunction has a diode characteristic, and the apparent photovoltaic effect of.3at.%Gd and 6at.%In is displayed under the light condition. The hybrid CdO film shows the best photovoltaic characteristics. The photoelectric conversion efficiency is 7.5%, the filling factor is 63%, the saturation current density (Jsc) and the open circuit voltage (Voc) are 11.4mA/cm2 and 1.04V. respectively. The results show that the CdO thin films doped with Gd and In are potential applications of the solar thin film battery mask.
4. using pulse laser deposition (PLD) to prepare the undoped CdO film on the ordinary glass substrate, the oxygen atmosphere pressure is 10Pa and the substrate temperature is 25. The annealed film is annealed in the muffle furnace. The annealing temperature and the annealing time are 200 and 30min. using single beam femtosecond laser pulse on the surface of the CdO film. The pulse repetition frequency is induced by the periodic nanoscale fringe structure. The central wavelength of the output laser pulse is 800nm, the pulse width is 100fs, the repetition rate is 1~2500Hz, and the single pulse energy is 2mJ. by FE-SEM. After 2000 pulses, the surface of the CdO film shows a short periodic fringes micro structure, the fringe period is 150~170n M. when the number of pulses is greater than 2000, the micro structure of a fluffy nano foam begins to appear on the CdO surface. The UV-VIS test of the supporting integral ball shows that the CdO film with a femtosecond laser micro structure has the characteristics of wide frequency and high absorption. The Hall effect test shows that the highest carrier concentration of the CdO film is 1.9 x 1021cm-3 when the number of pulses is 2000. On the basis of the minimum resistivity of 1.3 x 10-5 Omega cm., the CdO/p-Si heterojunction prepared by the femtosecond laser micro structure film shows good rectifying characteristics under the dark and light conditions. The I-V characteristic curve of the illumination condition shows that the heterojunction has the photovoltaic characteristics and the optimum open circuit voltage of the solar cell is Voc 0.55V, The short circuit current Jsc is 6.8mA/cm2, the filling factor is 29.1%. The wide frequency and high absorption characteristic of the 1.1%. femtosecond laser micro structure film makes it have potential applications in many optoelectronic devices, such as photovoltaic devices, charge coupling devices and photodetectors.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TB383.2

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