Ga掺杂ZnO透明导电薄膜的制备与光电性能研究
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摘要
氧化锌(ZnO)是II-VI族直接带隙(3.3eV)半导体氧化物,由于其优良的光电特性等,在发光器件、紫外探测器、太阳能电池、气敏元件以及声表面波器件等领域得到了广泛的应用。与现在常用的透明导电(TCO)薄膜ITO和SnO2:F薄膜相比,ZnO薄膜具有价格便宜,在活性氢和氢等离子体环境下稳定性高等优点而备受青睐。为提高ZnO的导电性能,常采用Al、In、Ga等元素掺杂,由于Ga的离子半径和共价键长度(0.62 ?和1.26 ?)与Zn非常相近(0.74 ?和1.34 ?),高掺杂浓度下导致ZnO的晶格畸也较小,因此,有必要研究Ga掺杂ZnO(GZO)薄膜,以期获得质量更优的TCO膜。
本文采用射频磁控溅射法在玻璃衬底上制备了高质量的GZO透明导电膜,研究了衬底温度、Ga掺杂浓度、薄膜厚度等对薄膜性能的影响;用XRD、AFM、SEM、XPS和紫外-可见双光束分光光度计等测试手段对沉积的薄膜进行了表征和分析;研究了薄膜的结构、电学、光学、热电性能。通过实验和研究分析,得出以下主要结果:
1.制备的GZO薄膜为六角纤锌矿多晶结构,具有(002)择优取向,晶粒大小为10~30nm,适量的Ga掺杂浓度及衬底温度能够提高结晶质量,增大晶粒尺寸,使薄膜表面更加致密。
2. XPS分析表明:Zn和Ga元素分别以Zn2+和Ga3+形式存在,未发现其它价态的Zn和Ga元素,薄膜中Ga含量比靶中Ga含量稍高。
3.膜厚、掺杂浓度、衬底温度对GZO薄膜的电阻率有较大影响,增大厚度、中等掺杂浓度、中等衬底温度,利于获得高导电性能。
4. GZO薄膜的可见光透射率平均值均在80%以上,随着掺杂浓度的提高,薄膜的光吸收边会向短波方向移动,发生“蓝移”现象,重掺杂又会导致“红移”产生,这与“B-M”效应和多体效应的联合作用有关。
5. GZO薄膜具有较强的热电效应,温差电动势为负,表明GZO为n型导电;随着膜厚增加,赛贝克系数增大;1at.%Ga掺杂时,Seebcek系数绝对值为最大值74.77μV/K。
6. GZO薄膜具有较强的磁阻效应,磁阻随磁场强度和薄膜迁移率的增大而增大。磁场强度为2.15T时,3at%Ga掺杂GZO薄膜的磁阻率为最大值0.77%。
7.综合光、电性能,提出沉积GZO薄膜的优化工艺条件为:掺杂浓度3at.%,衬底温度300℃,工作压强2Pa,靶基距7cm,功率160W。在此条件下制备的ZnO:Ga薄膜电阻率为1.44×10-3?.cm,平均透光率在80%以上,达到了透明导电膜的性能要求。
As a sort of optic-electrical information materials, transparent conductive oxide take up an extremely position. It can be widely used in many fields such as light-emitting device (LED, LD), solar cells, ultraviolet detectors, sensors, surface acoustic wave devices, flat panel liquid crystal displays, transparent electrodes and received extensive attention. Zinc oxide (ZnO) is a II-VI oxides with wide bandgap,which is n-type semiconductor material with hexagonal crystal structure. Defects and were easy to dope in ZnO, Compared to tin oxide (ITO) and SnO2, the abundant raw materials, low cost, relatively low deposition temperature and stability in hydrogen plasma environment are all the advantages it has, Ga doped ZnO films (GZO) have excellent optical properties comparable to the ITO thin films (high visible light transmittance and low resistivity), which has become one of the hot area of research.
The surface morphology and structural properties were studied by XRD, SEM, AFM, UV-visible, spectrophotometer was used to detect transmission, reflectance and other optical properties of film in all the spectral region.
Van der Pauw method was applied to measure the electrical properties and analyze the conduction mechanism of thin films. This paper also studied the thermal characteristics and the magnetoresistive characteristics of GZOthin film. Through experiments and analysis, the following conclusions were shown as follows:
1. GZO films are polycrystalline with hexagonal structure and (002) preferred orientation. The grain size is 10 ~ 30nm. the appropriate amount of Ga doping concentration and substrate temperature can improve the crystalline quality, increase the grain size and make the surface of films more dense.
2. XPS analysis shows that: Zn and Ga elements existed in Zn2+ and Ga3+ form, respectively. No other valence can be found. The Ga content of the films is higher than the target.
3. Thickness, doping concentration, and substrate temperature have greater impacts on the resistivity of the GZO films, increasing the thickness, appropriate amount of doping concentration, substrate temperature can obtain a high conductivity.
4. The average visible light transmittance of thin film samples were above 80%, with the doping concentration increased, the optical absorption edge shifted to the shortwave, which is called "blue shift". Heavily doped level would lead to emergence of "red-shift".
5. GZO film has strong thermal effect, the EMF of GZO film is negative, indicating that GZO film is n-type conductor; as the film thickness increases, Seebeck coefficient increases; 1at.% Ga-doped sample has the maximum absolute value of Seebcek coefficient for 74.77μV / K.
6. GZO film has strong magnetoresistance. The reluctance increased with the increases of magnetic field strength and Hall mobility. When the magnetic field strength of 2.15T, the maximum reluctance was 0.77%, which can be obtained for the 3at% Ga doped GZO films.
7. Take optical, electrical properties into consideration, the optimum conditions for the preparation of GZO film are: Doping concentration of 3at.%, working pressure of 2Pa, power of 160W, target distance of 7cm, on the Substrate temperature of 300℃. The lowest resistivity is 1.44×10-3?.cm, the average light transmission rate is beyond 80%, met the performance requirements of transparent conductive film.The sample with doping concentration of 1at.% has the highest thermoelectric power of 74.77.μV / K.
本文采用射频磁控溅射法在玻璃衬底上制备了高质量的GZO透明导电膜,研究了衬底温度、Ga掺杂浓度、薄膜厚度等对薄膜性能的影响;用XRD、AFM、SEM、XPS和紫外-可见双光束分光光度计等测试手段对沉积的薄膜进行了表征和分析;研究了薄膜的结构、电学、光学、热电性能。通过实验和研究分析,得出以下主要结果:
1.制备的GZO薄膜为六角纤锌矿多晶结构,具有(002)择优取向,晶粒大小为10~30nm,适量的Ga掺杂浓度及衬底温度能够提高结晶质量,增大晶粒尺寸,使薄膜表面更加致密。
2. XPS分析表明:Zn和Ga元素分别以Zn2+和Ga3+形式存在,未发现其它价态的Zn和Ga元素,薄膜中Ga含量比靶中Ga含量稍高。
3.膜厚、掺杂浓度、衬底温度对GZO薄膜的电阻率有较大影响,增大厚度、中等掺杂浓度、中等衬底温度,利于获得高导电性能。
4. GZO薄膜的可见光透射率平均值均在80%以上,随着掺杂浓度的提高,薄膜的光吸收边会向短波方向移动,发生“蓝移”现象,重掺杂又会导致“红移”产生,这与“B-M”效应和多体效应的联合作用有关。
5. GZO薄膜具有较强的热电效应,温差电动势为负,表明GZO为n型导电;随着膜厚增加,赛贝克系数增大;1at.%Ga掺杂时,Seebcek系数绝对值为最大值74.77μV/K。
6. GZO薄膜具有较强的磁阻效应,磁阻随磁场强度和薄膜迁移率的增大而增大。磁场强度为2.15T时,3at%Ga掺杂GZO薄膜的磁阻率为最大值0.77%。
7.综合光、电性能,提出沉积GZO薄膜的优化工艺条件为:掺杂浓度3at.%,衬底温度300℃,工作压强2Pa,靶基距7cm,功率160W。在此条件下制备的ZnO:Ga薄膜电阻率为1.44×10-3?.cm,平均透光率在80%以上,达到了透明导电膜的性能要求。
As a sort of optic-electrical information materials, transparent conductive oxide take up an extremely position. It can be widely used in many fields such as light-emitting device (LED, LD), solar cells, ultraviolet detectors, sensors, surface acoustic wave devices, flat panel liquid crystal displays, transparent electrodes and received extensive attention. Zinc oxide (ZnO) is a II-VI oxides with wide bandgap,which is n-type semiconductor material with hexagonal crystal structure. Defects and were easy to dope in ZnO, Compared to tin oxide (ITO) and SnO2, the abundant raw materials, low cost, relatively low deposition temperature and stability in hydrogen plasma environment are all the advantages it has, Ga doped ZnO films (GZO) have excellent optical properties comparable to the ITO thin films (high visible light transmittance and low resistivity), which has become one of the hot area of research.
The surface morphology and structural properties were studied by XRD, SEM, AFM, UV-visible, spectrophotometer was used to detect transmission, reflectance and other optical properties of film in all the spectral region.
Van der Pauw method was applied to measure the electrical properties and analyze the conduction mechanism of thin films. This paper also studied the thermal characteristics and the magnetoresistive characteristics of GZOthin film. Through experiments and analysis, the following conclusions were shown as follows:
1. GZO films are polycrystalline with hexagonal structure and (002) preferred orientation. The grain size is 10 ~ 30nm. the appropriate amount of Ga doping concentration and substrate temperature can improve the crystalline quality, increase the grain size and make the surface of films more dense.
2. XPS analysis shows that: Zn and Ga elements existed in Zn2+ and Ga3+ form, respectively. No other valence can be found. The Ga content of the films is higher than the target.
3. Thickness, doping concentration, and substrate temperature have greater impacts on the resistivity of the GZO films, increasing the thickness, appropriate amount of doping concentration, substrate temperature can obtain a high conductivity.
4. The average visible light transmittance of thin film samples were above 80%, with the doping concentration increased, the optical absorption edge shifted to the shortwave, which is called "blue shift". Heavily doped level would lead to emergence of "red-shift".
5. GZO film has strong thermal effect, the EMF of GZO film is negative, indicating that GZO film is n-type conductor; as the film thickness increases, Seebeck coefficient increases; 1at.% Ga-doped sample has the maximum absolute value of Seebcek coefficient for 74.77μV / K.
6. GZO film has strong magnetoresistance. The reluctance increased with the increases of magnetic field strength and Hall mobility. When the magnetic field strength of 2.15T, the maximum reluctance was 0.77%, which can be obtained for the 3at% Ga doped GZO films.
7. Take optical, electrical properties into consideration, the optimum conditions for the preparation of GZO film are: Doping concentration of 3at.%, working pressure of 2Pa, power of 160W, target distance of 7cm, on the Substrate temperature of 300℃. The lowest resistivity is 1.44×10-3?.cm, the average light transmission rate is beyond 80%, met the performance requirements of transparent conductive film.The sample with doping concentration of 1at.% has the highest thermoelectric power of 74.77.μV / K.
引文
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