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用于电-光应用的等离子体辅助低温电子束沉积的NiO薄膜

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发表于 2018-3-15 10:29:39 | 显示全部楼层 |阅读模式
Plasma assisted low temperature electron beam deposited NiO thin films for electro-optic applications
用于电-光应用的等离子体辅助低温电子束沉积的NiO薄膜

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 36, 031501 (2018)
https://doi.org/10.1116/1.5013126
Mustafa Burak Cosar
  Metallurgical and Materials Engineering Department, Middle East Technical University, Universiteler Mah. Dumlupinar Blv. No:1, 06800 Cankaya, Ankara, Turkey; Microelectronics, Guidance and Electro-Optics Division, Aselsan Inc., Cankırı Yolu 7. Km, 06750

ABSTRACT
摘要


This study aims to create high quality nickel oxide (NiO) thin films at low temperatures, which is a prerequisite for coatings on temperature sensitive substrates. NiO chunks were evaporated by electron beam source, and NiO thin films were deposited at a thickness value around 250 nm.

Depositions were performed at different experimental conditions: oxygen flow rate, deposition temperature, deposition rate, and plasma assistance. Deposited films were analyzed with regard to the structural, optical, and electrical aspects. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy results reveal that films are grown in cubic nickel oxide phase with preferred orientation of (111) plane. Nonstoichiometry of NiO films increases with increasing oxygen flow rate and plasma assistance leads to stoichiometric NiO films. Needle, spherical, and cuboidal particle formation were seen in scanning electron microscopy (SEM) images. Grain size, lattice parameter, and grain morphology were used to explain the variations in optical and electrical properties. It was seen that the mobility of the films increases with oxygen flow rate because of enhanced grain size revealed by XRD calculations and SEM images. Plasma assistance dramatically lowers the resistivity to 150 Ω cm compared to nonassisted films possessing resistivities on the order of megaohm centimeter values. Although plasma assistance results in low mobility [0.2 cm2/(V s)], enhanced sheet carrier concentration (1.1 × 1013 cm−1) was found to be the major factor leading to high conductivity. This situation is related to denser films with higher crystallinity, which was detected from the refractive index spectrum and confirmed by SEM analysis. Optical absorption studies at 400–600 nm wavelengths revealed that absorption can be minimized by deposition under high oxygen flow rate, high deposition temperature, and low deposition rate conditions. Optical band gaps can be tuned by varying the oxygen flow rate, deposition temperature, and deposition rate. It was seen that the Fermi level and valence band minima of the films highly depend on the oxygen flow rate and can be engineered by manipulating the flow rate of oxygen and deposition conditions.

        本研究的目的是在低温下制造高质量的氧化镍(NiO)薄膜,这是在温度敏感基材上涂层的先决条件。NiO块体通过电子束源蒸发,经沉积的NiO薄膜的厚度约为250nm。在不同的实验条件下进行沉积:氧气流量,沉积温度,沉积速率和使用等离子体辅助手段。对沉积的膜进行了结构、光学和电气性质诸项分析。X-射线衍射(XRD)和X-射线光电子谱的结果表明,膜中生长的立方氧化镍相在(111)面择优取向。NiO薄膜的非化学计量配比随氧气流量的增加而增加,而等离子体辅助会导致化学计量配比的NiO薄膜。在扫描电子显微镜(SEM)图像中可见针状、球形和立方形颗粒的形成。使用晶粒尺寸、晶格参数和晶粒形态来解释光学和电学性质的变化。可以看出,随着氧气流量的增加,薄膜的迁移性增加,这是因为XRD计算和SEM图像揭示其晶粒尺寸增大。与未使用等离子体辅助方法得到的兆欧厘米数量级电阻率相比,等离子体辅助方法显著地降低电阻率至150Ωcm。虽然等离子体辅助导致低迁移率[0.2cm2 /(Vs)],但增强的薄层载流子浓度(1.1×1013cm-1)被认为是导致高电导率的主要因素。这种情况与更高密度的薄膜结晶度有关,这是从折射率光谱中检测到的,并可通过SEM分析确认。在400-600 nm波段的光吸收研究表明,通过在高氧流率、高沉积温度和低沉积速率条件下的沉积,可以使光吸收最小化。光学带隙可以通过改变氧气流量、沉积温度和沉积速率来调整。可以看出,薄膜的费米能级和价带极小值高度依赖于氧气流量,并且也可以通过操纵氧气流量和沉积条件来进行设计。



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