NiO 是一種岩鹽結構的 p-type 半導體。其應用相當廣泛，如透明導電薄膜、太陽能電池、電致變色及氣體感測器，這些應用都和 NiO 薄膜的導電性質息息相關。雖然過去有許多研究著眼於濺鍍參數和薄膜性質間的關係。然而，關於 NiO 薄膜的導電性質仍有幾個問題一直尚未釐清。
首先是關於主導 NiO 薄膜導電機構的主要缺陷。根據缺陷化學，p-type 半導體的主要載子為電洞，其源自於晶體結構中產生金屬離子的空位或氧離子的插入。然而，何者是 NiO 薄膜中的主要缺陷，多年來一直有所爭議。再者，當 NiO 薄膜曝露在大氣時，其電阻率會隨時間增加而增加，一般稱之為電性時效。電性時效的問題在 n-type 半導體中並不常見；在 p-type 半導體，相關的研究也鮮少被討論。然而，這個現象對於元件的壽命及應用卻有極為重大的影響。因此，不論是時效機構的探討或是時效現象的抑制對於 NiO 薄膜的研究都相當重要。最後則是討論有關 NiO 薄膜在真空環境下退火，薄膜從 NiO 還原成純 Ni的現象。過去雖然曾經有相關的報導被提出，但還原的機構仍尚未明朗。有鑑於此，本研究將針對以上所提及的主題設計相關實驗，以材料的觀點對於導電機構、時效機構、時效抑制及退火還原提出相關的研究結果。
關於導電機構方面。本研究以 NiO 陶瓷靶進行薄膜濺鍍沉積，利用濺鍍時的工作氣氛調整薄膜成份並沉積計量比不同的雙層薄膜。接著以 SIMS 及 XPS 進行縱深成份分析。結果顯示計量比的改變和薄膜中的 Ni 成份變化有關，NiO 薄膜中主要的缺陷應為 Ni 空位。此外，為了更進一步驗證實驗結果，本研究利用同步輻射吸收光譜量測計量比不同之 NiO 薄膜中的 Ni 及 O 原子配位數。結果顯示，當薄膜中過多的氧降低並趨近於理論值時，薄膜中 Ni 之最臨近的 O 原子 (first shell) 配位數並無太大變化；而 Ni 之最臨近的 Ni 原子 (second shell) 配位數會隨之增加並趨近於理論值。配位數的結果顯示 NiO 薄膜計量比的變化亦是導因於 Ni 原子數量的改變。因此，本研究判定非計量比之 NiO 薄膜中主要的點缺陷為 Ni 空位。
在電性時效方面，本研究將沉積後的 NiO 薄膜放置於不同的乾燥氣氛 (H2、CO、O2、CO2、N2及 Ar) 及不同濕度的 Ar下，量測薄膜在各種氣氛及濕度中，電阻隨時間的變化情形。結果顯示，還原性氣體和水氣吸附在 NiO 薄膜表面是造成電性時效的主要原因。這些吸附在薄膜表面的氣氛會和 NiO 形成化學鍵，鍵結的過程將電子傳導進入薄膜和電洞中和，造成薄膜電阻升高。
由於電性時效的結果導因於薄膜的表面吸附，且表面吸附和薄膜表面結構有關。因此，本研究分別利用增加基板溫度及 Li 掺雜來調整薄膜的表面結構以抑制時效的性質。研究結果顯示，提高基板溫度可以使 NiO 的優選方位由原來極性的 (111) 轉變為非極性的 (200)，且此轉變是從薄膜的最表面開始往基板方向進行。極性的 (111) 面具有較多懸鍵，會加速氣氛和薄膜的反應，的在薄膜表面生成非極性的 (200) 面可以有效降低時效速率。
Li 掺雜方面，本研究在 NiO 陶瓷靶上黏貼1~15片的 Li2O 圓錠，以共濺鍍的方式沉積不同 Li 含量的 NiO 薄膜。沉積後的薄膜分別以 WDS 及 ICP-MS 對薄膜進行定量分析。分析後得本研究之 Li 掺雜量範圍為0~16.18 at.%。研究結果發現，掺雜的 Li 容易偏析在空位或薄膜表面等缺陷位置。最初加入的 Li 填補到原本薄膜的 Ni 空位位置，造成薄膜非計量比程度及導電度下降。隨著 Li 含量的持續增加，部分的 Li 會偏析在薄膜的表面並且形成塊狀的凸起物。這些富 Li 的凸起物覆蓋在薄膜的表面可以隔絕大氣中的水氣和薄膜反應。此外，Li 掺雜後 (111) 面的繞射峰強度會隨之下降，顯示 Li 掺雜可以抑制 (111) 面的成長，因此 Li 掺雜亦可有效抑制 NiO 薄膜電性時效的問題。
在退火還原方面，本研究以不同的退火溫度、基板材料、退火氣氛及分析方法進行解析。結果發現，退火還原的現象和薄膜的計量比有關，且還原的部分主要是發生在薄膜最表面的100 nm處。

NiO has the rock salt structure of p-type semiconductors. Its electrical conductivity has made NiO useful in a wide range of applications, such as transparent conductive films, solar cells, electrochromic devices, and gas sensors. Although a number of reports have discussed the properties of sputtered NiO films for various parameters, some electrical properties of sputtered NiO are still unclear.
The dominant point defects in sputtered NiO films are unknown. According to defects chemistry, the major carriers of a p-type NiO semiconductor come from the vacancies of metal ions or the interstitial oxygen ions formed in NiO crystal. It is unclear which one is dominant. Sputtered NiO film experiences electrical aging. The resistivity of the sputtered film increases with time exposed to air. Electrical aging is not common in n-type semiconductors and it has been rarely discussed in p-type semiconductors. However, it greatly affects the longevity and applications of devices. Therefore, the study of its mechanism and suppression is very important. Finally, we discuss some reduction properties of NiO film annealed in a vacuum environment. Although reduction has been previously reported, its mechanism is still ambiguous.
To investigate the electrical conduction mechanism, an RF sputter and a NiO target were used to deposit NiO films. The composition of double layer films were adjusted by changing the working gas and the in-depth composition were measured by SIMS and XPS. The results show that the degree of non-stoichiometry of NiO films was determined by Ni content. Also, the coordination numbers of the annealed NiO films were measured by X-ray absorption spectroscopy to confirm the in-depth composition data. The results show that non-stoichiometry NiO contains more oxygen atoms than stoichiometric NiO. When the composition was made close to that of stoichiometry via the annealing process, the first coordination number shell does not change while the second coordination number shell increased, which implies that the composition change results from a change in Ni atoms. It was concluded that Ni vacancies are the dominant point defects that result in the electrical conductivity of NiO films.
To investigate electrical aging, stability tests were performed in various dry atmospheres (H2, CO, O2, CO2, N2 and Ar) and in a humid Ar environment. The stability was determined by measuring the resistance change with time. The results show that electrical aging was caused by the adsorption of reduction gas and water vapor, which injected electrons into the NiO film. These electrons then counteracted with the redundant electric holes and attenuated the charge carriers in the NiO film. This reaction lowered the carrier concentration; the electrical conductivity of NiO film subsequently decayed with time.
Electrical aging is due to gas adsorption; which greatly affected by film structure. In this study, the substrate temperature and Li doping were used to the suppress aging. The results show that an increase of substrate temperature changes the crystal structure. The preferred orientation changes from polar (111) into non-polar (200); this change starts from the top surface to the substrate. The dangling bonds on (111) surface increase the aging phenomena. The formation of non-polar (200) can decrease the aging rate of sputtered NiO films.
For Li doping, the concentration of Li in the thin films was adjusted by placing 0~15 Li2O disks on the target surface. The Li concentration in the films varied from 0 to 16.29 at.%, as determined by WDS and ICP-MS. The results show that the doped Li ions occupy crystal defect sites such as vacancies or segregate on the film surface. Initially, doped Li occupied the Ni vacancies in the film, decreasing electrical conductivity. When the Li concentration was further increased, some Li segregated on the film surface and formed bulges at high Li concentrations. These Li-rich oxides which covered the film surface served as partitions between the film and moisture from the atmosphere. Also, the doping process decreased the (111) peak, which means that it suppresses the formation of the (111) plane. As a result, the Li-doped NiO films show a relatively high arrestment to electrical resistance aging.
The effects of annealing temperature, substrate material, and gas atmosphere on reduction properties were studied. The results show that reduction is also related to the non-stoichiometry of the sputtered NiO films. The reduction occurs from the film surfaces and the reduction depth is about 100 nm.

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