Modulation of the characteristics of Bismuth thin films by a variety of thin down methods——morphology, crystalline and electrical properties

• Main Authors: Xinyou Liu, 劉心佑
• Other Authors: 林浩雄
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/967n9h

碩士 === 國立臺灣大學 === 電子工程學研究所 === 107 === In this thesis, the bismuth (Bi) film is grown on heavily doped, lightly doped ‎Silicon dioxide substrate, Silicon dioxide/ Silicon (SiO2/Si) substrate and ALD-grown aluminum oxide substrate by molecular beam epitaxy (MBE System). The thickness of the bismuth film is reduced by four different methods, and high-resolution X-ray diffraction (HRXRD), X-ray reflectometer (XRR), transmission electron microscope (TEM), scanning electron microscope (SEM), atomic force microscopy (AFM) is applied for measurement and material analysis during those reduction. Also, the electrical properties were checked. We found that sulfuric acid diluted with 125 times water can etch the bismuth film slowly. The mechanism of etching the bismuth film is preliminarily studied, that is, it will be etched faster at the grain boundary, so the longer etching time will bring island shape. And the conductivity followed the percolation theory. In addition, for the first time we applied UV-Ozone oxidation to reduce the thickness of the bismuth film and we found a suitable oxidation temperature. When the oxidation time is one hour, above 120°C, the bismuth is completely oxidized. We have found that the oxidation products under this condition are bismuth oxide and bismuth suboxide. The sheet resistance of the bismuth film during the oxidation process appears in three stages and eventually reaches saturation at a fixed temperature. At the same time, the longitudinal lateral oxidation anisotropy of bismuth is also consistent with its structural characteristics. Next, we studied the properties of bismuth thin film grown on the oxide layer and thinned its thickness by plasma etching (RIE) to investigate the electric field effect of it. The transistor exhibits the property of electronic conduction (N-channel FET), and a highest mobility of 486 cm^2/(Vs). Finally, we successfully used the mechanical exfoliation method to obtain a bismuth film of less than 100 nm on a 300 nm SiO2 substrate by Nitto tape. Using TEM and electron backscatter (EBSD) technics, we analyzed the direction perpendicular to the substrate follows (003) or (012). We also made theoretical values for the corresponding colors of the different thickness of the film on the substrate.