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用于電-光應用的等離子體輔助低溫電子束沉積的NiO薄膜

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發表于 2018-3-15 10:29:39 | 只看該作者 回帖獎勵 |倒序瀏覽 |閱讀模式
Plasma assisted low temperature electron beam deposited NiO thin films for electro-optic applications
用于電-光應用的等離子體輔助低溫電子束沉積的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溫下制造高質量的氧化鎳(NiO)薄膜,這是在溫度敏感基材上涂層的先決條件。NiO塊體通過電子束源蒸發,經沉積的NiO薄膜的厚度約為250nm。在不同的實驗條件下進行沉積:氧氣流量,沉積溫度,沉積速率和使用等離子體輔助手段。對沉積的膜進行了結構、光學和電氣性質諸項分析。X-射線衍射(XRD)和X-射線光電子譜的結果表明,膜中生長的立方氧化鎳相在(111)面擇優取向。NiO薄膜的非化學計量配比隨氧氣流量的增加而增加,而等離子體輔助會導致化學計量配比的NiO薄膜。在掃描電子顯微鏡(SEM)圖像中可見針狀、球形和立方形顆粒的形成。使用晶粒尺寸、晶格參數和晶粒形態來解釋光學和電學性質的變化。可以看出,隨著氧氣流量的增加,薄膜的遷移性增加,這是因為XRD計算和SEM圖像揭示其晶粒尺寸增大。與未使用等離子體輔助方法得到的兆歐厘米數量級電阻率相比,等離子體輔助方法顯著地降低電阻率至150Ωcm。雖然等離子體輔助導致低遷移率[0.2cm2 /(Vs)],但增強的薄層載流子濃度(1.1×1013cm-1)被認為是導致高電導率的主要因素。這種情況與更高密度的薄膜結晶度有關,這是從折射率光譜中檢測到的,并可通過SEM分析確認。在400-600 nm波段的光吸收研究表明,通過在高氧流率、高沉積溫度和低沉積速率條件下的沉積,可以使光吸收最小化。光學帶隙可以通過改變氧氣流量、沉積溫度和沉積速率來調整。可以看出,薄膜的費米能級和價帶極小值高度依賴于氧氣流量,并且也可以通過操縱氧氣流量和沉積條件來進行設計。



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