SnO_2：F薄膜的光电特性
摘要
透明导电薄膜，象SnO2:F薄膜有着很多的优点，由于它们的独特属性，比如高电导率，可见光区高透过，红外光区的高反射，非常好的化学稳定性，热稳定性等，以上所提到的属性，使它可以应用到很多的领域，例如制备太阳能电池的透明电极，显示设备，高灵敏度的气敏设备，绝缘低辐射玻璃等。有很多的方法制备SnO2:F薄膜，但溅射法和溶胶—凝胶法是相当简单和便宜的，这篇论文详细介绍了溶胶—凝胶法在玻璃基板上制备SnO2:F薄膜。
这篇论文共包括四个部分：第一部分为基础知识，介绍了SnO2:F薄膜的光电属性；第二部分 介绍了测量薄膜光学常数的两种方法；第三部分介绍了在玻璃基板上制备SnO2:F薄膜的具体方法和过程；第四部分对样品数据进行了分析和讨论。这里我们重点介绍一下实验部分与测量的结果。
基础理论部分
包括半导体能带理论，光学特性测试技术，电磁波在等离子体中传播理论。
实验部分
在我们的工作中，锡的先驱液，用纯的SnCl4.5H2O解析,溶剂是酒精与水的混合物。制成的溶液包括每升0.5-0.9摩尔的SnCl4 和 酒精与水的混合物。NH4F 按照F/Sn 比为0-1.2的比例加入。
实验装置如图1所示
图1.实验装置图
它包括一个超声波发生装置和沉积反应堆。SnCl4溶液装在玻璃烧瓶中，通过底部的传感器来产生溶胶。由传感器产生的超声波，穿过水和烧瓶底部，在SnCl4溶液的表面聚焦，产生一个喷泉。2Mz的传感器产生的雾滴直径大概在3-4微米左右，适合溶胶法的工作条件。作为载气的压缩气体，带着产生的雾滴到反应堆。底板的支架是一个旋转的平板,固定在加热器上，喷嘴宽60毫米，长50毫米，厚度1.5毫米，固定在旋转板上方60毫米的高度。底板的温度用热电偶控制，信号被反馈到一个自动温度调节装置。所有的SnO2:F薄膜都沉积在玻璃底板上。通过透射光谱和椭偏仪测量薄膜的光学常数。红外光谱测量通过Hitachi U－4100分光光度计，面电阻通过四探针仪器来测量。
样品制备
直到目前，甲醇和乙醇一直被用于溶胶方法制备薄膜。但溶液有一个严重的缺点，就是在高温基板处极易燃烧。在我们的工作中，我们选择
SnCl4作为SnO2膜的先驱液，NH4F作为掺杂。为了安全起见，我们增加了溶液中水的成分，根据沉淀过程原理，沉淀的条件被严格限制。
不同的溶液成分的实验结果，列在表1。沉积参数为底板温度450，喷嘴与底板距离60mm，载气8L/MIN，溶液中包括 0.7M SnCl4·5H2O, 0.4M NH4F。
表1. 溶液成分，可操作性，膜表面性质，面电阻
C2H5OH百分比含量
可操作性
膜表面性质
面电阻
(Ω/sq.)
95%C2H5OH/5% H2O
易燃烧
乳白色
19,22,84
80% C2H5OH/20% H2O
易燃烧
乳白色
16,18,42,
60%C2H5OH/40% H2O
较易燃烧
透明
7,10,8
50%C2H5OH/50% H2O
不易燃烧
透明
2,2,1
25% C2H5OH/75% H2O
不易燃烧
乳白色
2,4,5
通过表1可以看出50% C2H5OH/50% H2O成分沉积的薄膜，面电阻为2Ω/sq，不仅易操作，而且适合制成高质量的SnO2:F薄膜。
光学常数测量
厚度同样也是影响薄膜性能的一个重要参数，在我们的研究过程中，用了两种方法来测量薄膜的厚度，第一种方法：透射光谱的方法；第二种方法：利用椭偏仪测量。
透射光谱法是一种方便快捷的方法，它利用可见光波段的干涉条纹，来计算膜厚度和折射率。根据干涉原理2nd=m，透射光会产生干涉条纹，当m=1.2.3..时，对应着光谱的波峰位置，当m=0.5,1.5,….时对应着光谱的波谷位置，我们用相邻的波峰与波谷的数据作差，就会得到厚度
，其中，为波峰与波谷所对应的波长，可以从光度计直接读出，n为该波长的折射率，可以利用文献[1]中所给的经验公式
计算得到。
其中s为基底的折射率，TM,Tm分别为该波长对应的极大值与极小值。我们用的仪器是TU-1901双光束分光光度计。测量程序是用Cbuilder软件开发的。我们利用已知数据的样品对该方法进行校准，得到的误差为2%。椭偏仪测量方法是一种非常精确的方法，它利用反射光的偏振方向变化，来计算薄膜的厚度和折射率。我们用以上两种方法分别对3个样品进行了测量，分别得到了以下的数据：
表2. 厚度测量结果
透射光谱测量, nm
椭偏仪测量, nm
样品1
319±10
369.2
样品2
649±10
571.7
样品3
253±10
272.3
图2.样品的可见光透射曲线
掺杂比例
表3的数据表明当溶液中0.3－0.5 mol NH4F 和 0.7 mol SnCl 4·5H2O的比例时，面电阻低且膜表面的质量好，对应着较高的导电率。
表 3. 实验数据
前驱液 SnCl4·5H2O
浓度 (mol 1-1)
NH4F浓度
(mol 1-1)
面电阻
(Ω/sq.)
膜表面性质
0.7
0
12,14,28
透明 或 发白
0.7
0.1
4,9,11
透明
0.7
0.2
3,6,8
透明
0.7
0.3
2,3,7
透明
0.7
0.4
2,3,5
透明
0.7
0.5
3,6,8
透明
0.7
0.6
4,12,20
透明
SnO2:F薄膜红外反射
SnO2:F薄膜的红外反射率，对于研究低辐射玻璃是非常重要的，但直到现在有关的报道仍然
Transparent conducting films such as SnO2 with fluorine doping are of widespread interest because of their unique properties. These include: high electrical conductivity; good transmittance in visible spectrum region and high reflectance in infrared wavelengths; excellent chemical, mechanical and thermal stability. The above mentioned properties make them very useful for many fields of application: transparent electrodes for silicon and Cds/Cdte solar cells, display devices, high sensitive gas sensors and high-insulation low-emissivity glasses.
This paper is divided into four parts, the first part is the theory about photoelectric characteristic of SnO2:F film ;the second part is about the determination of optical index; the third part is deposition of SnO2:F film;the last one is discussion and result.
In this paper we demonstrate how to deposit a good-quality fluorine-doped film, including tin precursor solution preparation, solvent composition, carrier gas and deposition temperature. The mechanism of fluorine doping is discussed on the basis of experimental results and relationship between the sheet resistances and infrared transmission spectra of SnO2:F are shown in the present paper.
There are many processes for deposition of SnO2 films, but spray pyrolysis and pyrosol deposition process are fairly simple and inexpensive. Several years ago atmospheric pressure chemical vapour deposition(APCVD) was mostly used as deposition process for oxide thin film in industrial application, and pyrosol process was a laboratorial technique only. Recently, pyrosol process has developed rapidly and will definitely find application in industry in the near future.
The fluorine-doped SnO2 films(SnO2:F films) have been produced for improvement of their optical and electrical properties, especially for decreasing electrical resistance, but the mechanism concerning fluorine doping is reported very limited up to now.
The experimental set-up for deposition of SnO2:F films is shown in Fig1.
It consists of an ultrasonic atomizer and a deposition reactor. A glass flask containing SnCl4 solution was used for generation of aerosol by a transducer installed under the bottom of the flask. The ultrasound generated by the transducer penetrates the water, glass bottom and slightly focused near by the SnCl4 solution surface to raise up a “geyser”. The droplets generated by transducer working at 2Mz in our system are 3-4 μm and are suitable for pyrosol process. Compressed air was used as carrier gas to carry the mist to deposition reactor. The outer covering of the reactor consists of a upper glass cover and a lower ceramic sleeve which is located nearly to the heater. The substrate holder is a rotating plate mounted above the heater. The nozzle has a flat bill of 60 mm in width, 50mm in length, and 1.5mm in thickness on the inside and is fixed at a height of 50-60mm above the rotating plate. Temperature of substrate was measured by using a thermocouple and the signal was fed to a thermostat to control the temperature of substrate.
All the SnO2:F film depositions were carried out on silica-coated soda-lime glass substrates (10cm×10cm). The film thickness was determined by transmission spectra in the visible region measured with TU-1901 UV-VIS spectrophotometer of Beijing Purkinje General Instrument Co., Ltd and a ellipsometer for comparison. The infrared transmission spectra was measured with Hitachi U－4100 Spectrophotometer up to 2500nm.The sheet resistance of the SnO2:F film was measured with a four-point probe.
Up to the present, methanol and ethanol were used for most research works in the pyrosol process. But alcohol solvents have a serious weakness of flammability especially near by a high-temperature substrate in air. In this work we have chosen SnCl4·5H2O as precursor of SnO2 film and NH4F as dopant. For the purpose of safety, an increase of water content in the solvent has been expected. According to the deposition mechanism of pyrosol process, the deposition parameters are critical under the inf
这篇论文共包括四个部分：第一部分为基础知识，介绍了SnO2:F薄膜的光电属性；第二部分 介绍了测量薄膜光学常数的两种方法；第三部分介绍了在玻璃基板上制备SnO2:F薄膜的具体方法和过程；第四部分对样品数据进行了分析和讨论。这里我们重点介绍一下实验部分与测量的结果。
基础理论部分
包括半导体能带理论，光学特性测试技术，电磁波在等离子体中传播理论。
实验部分
在我们的工作中，锡的先驱液，用纯的SnCl4.5H2O解析,溶剂是酒精与水的混合物。制成的溶液包括每升0.5-0.9摩尔的SnCl4 和 酒精与水的混合物。NH4F 按照F/Sn 比为0-1.2的比例加入。
实验装置如图1所示
图1.实验装置图
它包括一个超声波发生装置和沉积反应堆。SnCl4溶液装在玻璃烧瓶中，通过底部的传感器来产生溶胶。由传感器产生的超声波，穿过水和烧瓶底部，在SnCl4溶液的表面聚焦，产生一个喷泉。2Mz的传感器产生的雾滴直径大概在3-4微米左右，适合溶胶法的工作条件。作为载气的压缩气体，带着产生的雾滴到反应堆。底板的支架是一个旋转的平板,固定在加热器上，喷嘴宽60毫米，长50毫米，厚度1.5毫米，固定在旋转板上方60毫米的高度。底板的温度用热电偶控制，信号被反馈到一个自动温度调节装置。所有的SnO2:F薄膜都沉积在玻璃底板上。通过透射光谱和椭偏仪测量薄膜的光学常数。红外光谱测量通过Hitachi U－4100分光光度计，面电阻通过四探针仪器来测量。
样品制备
直到目前，甲醇和乙醇一直被用于溶胶方法制备薄膜。但溶液有一个严重的缺点，就是在高温基板处极易燃烧。在我们的工作中，我们选择
SnCl4作为SnO2膜的先驱液，NH4F作为掺杂。为了安全起见，我们增加了溶液中水的成分，根据沉淀过程原理，沉淀的条件被严格限制。
不同的溶液成分的实验结果，列在表1。沉积参数为底板温度450，喷嘴与底板距离60mm，载气8L/MIN，溶液中包括 0.7M SnCl4·5H2O, 0.4M NH4F。
表1. 溶液成分，可操作性，膜表面性质，面电阻
C2H5OH百分比含量
可操作性
膜表面性质
面电阻
(Ω/sq.)
95%C2H5OH/5% H2O
易燃烧
乳白色
19,22,84
80% C2H5OH/20% H2O
易燃烧
乳白色
16,18,42,
60%C2H5OH/40% H2O
较易燃烧
透明
7,10,8
50%C2H5OH/50% H2O
不易燃烧
透明
2,2,1
25% C2H5OH/75% H2O
不易燃烧
乳白色
2,4,5
通过表1可以看出50% C2H5OH/50% H2O成分沉积的薄膜，面电阻为2Ω/sq，不仅易操作，而且适合制成高质量的SnO2:F薄膜。
光学常数测量
厚度同样也是影响薄膜性能的一个重要参数，在我们的研究过程中，用了两种方法来测量薄膜的厚度，第一种方法：透射光谱的方法；第二种方法：利用椭偏仪测量。
透射光谱法是一种方便快捷的方法，它利用可见光波段的干涉条纹，来计算膜厚度和折射率。根据干涉原理2nd=m，透射光会产生干涉条纹，当m=1.2.3..时，对应着光谱的波峰位置，当m=0.5,1.5,….时对应着光谱的波谷位置，我们用相邻的波峰与波谷的数据作差，就会得到厚度
，其中，为波峰与波谷所对应的波长，可以从光度计直接读出，n为该波长的折射率，可以利用文献[1]中所给的经验公式
计算得到。
其中s为基底的折射率，TM,Tm分别为该波长对应的极大值与极小值。我们用的仪器是TU-1901双光束分光光度计。测量程序是用Cbuilder软件开发的。我们利用已知数据的样品对该方法进行校准，得到的误差为2%。椭偏仪测量方法是一种非常精确的方法，它利用反射光的偏振方向变化，来计算薄膜的厚度和折射率。我们用以上两种方法分别对3个样品进行了测量，分别得到了以下的数据：
表2. 厚度测量结果
透射光谱测量, nm
椭偏仪测量, nm
样品1
319±10
369.2
样品2
649±10
571.7
样品3
253±10
272.3
图2.样品的可见光透射曲线
掺杂比例
表3的数据表明当溶液中0.3－0.5 mol NH4F 和 0.7 mol SnCl 4·5H2O的比例时，面电阻低且膜表面的质量好，对应着较高的导电率。
表 3. 实验数据
前驱液 SnCl4·5H2O
浓度 (mol 1-1)
NH4F浓度
(mol 1-1)
面电阻
(Ω/sq.)
膜表面性质
0.7
0
12,14,28
透明 或 发白
0.7
0.1
4,9,11
透明
0.7
0.2
3,6,8
透明
0.7
0.3
2,3,7
透明
0.7
0.4
2,3,5
透明
0.7
0.5
3,6,8
透明
0.7
0.6
4,12,20
透明
SnO2:F薄膜红外反射
SnO2:F薄膜的红外反射率，对于研究低辐射玻璃是非常重要的，但直到现在有关的报道仍然
Transparent conducting films such as SnO2 with fluorine doping are of widespread interest because of their unique properties. These include: high electrical conductivity; good transmittance in visible spectrum region and high reflectance in infrared wavelengths; excellent chemical, mechanical and thermal stability. The above mentioned properties make them very useful for many fields of application: transparent electrodes for silicon and Cds/Cdte solar cells, display devices, high sensitive gas sensors and high-insulation low-emissivity glasses.
This paper is divided into four parts, the first part is the theory about photoelectric characteristic of SnO2:F film ;the second part is about the determination of optical index; the third part is deposition of SnO2:F film;the last one is discussion and result.
In this paper we demonstrate how to deposit a good-quality fluorine-doped film, including tin precursor solution preparation, solvent composition, carrier gas and deposition temperature. The mechanism of fluorine doping is discussed on the basis of experimental results and relationship between the sheet resistances and infrared transmission spectra of SnO2:F are shown in the present paper.
There are many processes for deposition of SnO2 films, but spray pyrolysis and pyrosol deposition process are fairly simple and inexpensive. Several years ago atmospheric pressure chemical vapour deposition(APCVD) was mostly used as deposition process for oxide thin film in industrial application, and pyrosol process was a laboratorial technique only. Recently, pyrosol process has developed rapidly and will definitely find application in industry in the near future.
The fluorine-doped SnO2 films(SnO2:F films) have been produced for improvement of their optical and electrical properties, especially for decreasing electrical resistance, but the mechanism concerning fluorine doping is reported very limited up to now.
The experimental set-up for deposition of SnO2:F films is shown in Fig1.
It consists of an ultrasonic atomizer and a deposition reactor. A glass flask containing SnCl4 solution was used for generation of aerosol by a transducer installed under the bottom of the flask. The ultrasound generated by the transducer penetrates the water, glass bottom and slightly focused near by the SnCl4 solution surface to raise up a “geyser”. The droplets generated by transducer working at 2Mz in our system are 3-4 μm and are suitable for pyrosol process. Compressed air was used as carrier gas to carry the mist to deposition reactor. The outer covering of the reactor consists of a upper glass cover and a lower ceramic sleeve which is located nearly to the heater. The substrate holder is a rotating plate mounted above the heater. The nozzle has a flat bill of 60 mm in width, 50mm in length, and 1.5mm in thickness on the inside and is fixed at a height of 50-60mm above the rotating plate. Temperature of substrate was measured by using a thermocouple and the signal was fed to a thermostat to control the temperature of substrate.
All the SnO2:F film depositions were carried out on silica-coated soda-lime glass substrates (10cm×10cm). The film thickness was determined by transmission spectra in the visible region measured with TU-1901 UV-VIS spectrophotometer of Beijing Purkinje General Instrument Co., Ltd and a ellipsometer for comparison. The infrared transmission spectra was measured with Hitachi U－4100 Spectrophotometer up to 2500nm.The sheet resistance of the SnO2:F film was measured with a four-point probe.
Up to the present, methanol and ethanol were used for most research works in the pyrosol process. But alcohol solvents have a serious weakness of flammability especially near by a high-temperature substrate in air. In this work we have chosen SnCl4·5H2O as precursor of SnO2 film and NH4F as dopant. For the purpose of safety, an increase of water content in the solvent has been expected. According to the deposition mechanism of pyrosol process, the deposition parameters are critical under the inf
引文
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