本文選題：碳化硅　切入點：氫鈍化表面　出處：《江蘇大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：碳化硅(SiC)是一種物理化學(xué)性質(zhì)優(yōu)良、應(yīng)用前景廣闊的的寬禁帶半導(dǎo)體材料。無論是作為結(jié)構(gòu)材料還是功能材料,SiC表面的結(jié)構(gòu)及其相應(yīng)的物理化學(xué)性質(zhì)對其在諸多領(lǐng)域的應(yīng)用至關(guān)重要,特別是氫鈍化的4H-SiC(0001)表面,由于其在新一代電子器件以及二維納米薄膜制備領(lǐng)域獨特的優(yōu)勢,對其表面的微觀結(jié)構(gòu)、狀態(tài)以及物理化學(xué)性質(zhì)進行原子尺度的深入探索顯得尤為重要。本研究基于第一性原理計算,從原子尺度系統(tǒng)研究了七種代表性的點缺陷(包括ISi、IC、VSi、VC、CSi、SiC、CSiSiC)對氫鈍化的4H-SiC(0001)表面結(jié)構(gòu)的影響,并系統(tǒng)考察了這幾類表面缺陷與兩種常用表面改性金屬原子(Ag、Mo)之間的相互吸附作用以及對表面電子能帶結(jié)構(gòu)的影響。具體內(nèi)容和結(jié)論如下:首先,我們計算了位于氫鈍化4H-SiC(0001)面的七種點缺陷的形成能和微觀結(jié)構(gòu),細致考察了以上點缺陷隨著深度變化對近鄰晶格變形的影響程度,并分析晶格變形與形成能之間的關(guān)系,從而系統(tǒng)比較以上缺陷分別在4H-SiC體相、理想(0001)表面和氫鈍化(0001)表面的形成能大小關(guān)系及相應(yīng)的熱力學(xué)穩(wěn)定性。此外,我們分別研究了晶胞大小、化學(xué)勢對點缺陷形成能的影響,并根據(jù)形成能大小估算了這些缺陷的在不同溫度下的熱力學(xué)濃度。結(jié)果表明,填隙缺陷的結(jié)構(gòu)在氫鈍化面是不穩(wěn)定的。除了碳填隙缺陷和碳空位缺陷,其他缺陷的形成能隨層數(shù)的增加而增加。而且除反位缺陷,其他缺陷的形成能比體內(nèi)缺陷的形成能低,但是比理想表面的形成能高。其次,通過計算結(jié)合能,我們比較了氫鈍化4H-SiC(0001)表面不同點缺陷對兩種金屬原子(Ag、Mo)吸附性強弱,并結(jié)合二次差分電荷密度對其相互作用下的電荷轉(zhuǎn)移及成鍵情況進行了細致的表征分析,揭示了其相互作用強弱差異的主要原因,同時在理論上解釋了SiC表面金屬離子注入后,其表面金屬化以及表面潤濕性提高的微觀物理機制。計算結(jié)果表明,與無缺陷的氫鈍化表面相比,帶有懸掛鍵的點缺陷(如空位、填隙原子)能夠顯著提高對Ag(Mo)的吸附性能。其最高吸附性能提高比例分別高達4150%(238.1%)。另外,通過電子能帶和態(tài)密度計算,我們分析比較了點缺陷以及吸附金屬原子對氫鈍化4H-SiC(0001)表面的電子性質(zhì)的影響。結(jié)果顯示,對(0001)表面進行氫鈍化能夠消除理想表面的附加能級,使得導(dǎo)帶底和價帶頂上移。表面點缺陷以及吸附的金屬能夠在禁帶區(qū)域引入附加能級,其中以深能級為主。金屬Ag(Mo)的吸附能夠增加體系的磁矩,并且吸附Mo引入的附加能級數(shù)目多于Ag。
[Abstract]:Sic is a kind of excellent physical and chemical properties. The structure of sic surface and its corresponding physical and chemical properties are very important for its application in many fields, especially the hydrogen passivated 4H-SiCn0001 surface, which is widely used as a wide band gap semiconductor material, both as a structural material and as a functional material, and its corresponding physical and chemical properties are very important for its application in many fields, especially the hydrogen passivated 4H-SiCn001 surface. Due to its unique advantages in the new generation of electronic devices and the preparation of two-dimensional nanocrystalline films, It is very important to explore the state and physicochemical properties at atomic scale. The effects of seven representative point defects (including ISi-ICVSi-VSi-CSi-CSiC- CSiC- CSiCon) on the surface structure of hydrogen-passivated 4H-SICP _ (0001) have been studied by atomic scale system. The interaction between these kinds of surface defects and two commonly used surface modified metal atoms (Ag-Mo) and their effects on the surface electronic band structure are also systematically investigated. The specific contents and conclusions are as follows: first of all, We have calculated the formation energy and microstructure of seven kinds of point defects located on the hydrogen passivated 4H-SiCn0001) surface. We have carefully investigated the influence of the above point defects on the lattice deformation of the nearest neighbor with the change of depth, and analyzed the relationship between the lattice deformation and the formation energy. Therefore, the relationship between the formation energy and the thermodynamic stability of the above defects on the 4H-SiC, ideal and hydrogen passivated surfaces are systematically compared. In addition, the effects of the cell size and the chemical potential on the formation energy of the point defects are studied respectively. The thermodynamic concentration of these defects at different temperatures is estimated according to the formation energy. The results show that the structure of the interstitial defects is unstable on the hydrogen passivation surface, except for the carbon filling defects and the carbon vacancy defects. The formation energy of other defects increases with the increase of the number of layers. Besides, the formation energy of other defects is lower than that of internal defects, but higher than that of ideal surface. Secondly, the binding energy is calculated. In this paper, we compare the adsorption of two kinds of metal atoms with different defects on the surface of hydrogen passivated 4H-SiO _ (0001), and analyze the charge transfer and bond formation under the interaction of the two metal atoms by combining with the secondary differential charge density. The main reasons for the difference of interaction are revealed, and the microphysical mechanism of surface metallization and surface wettability improvement after metal ion implantation on SiC surface is theoretically explained. In comparison with non-defect hydrogen passivated surfaces, point defects with hanging bonds (such as vacancies, interstitial atoms) can significantly improve the adsorption properties of Agnimo. The highest adsorbability can be increased by up to 4150% and 238.1%, respectively. By calculating the electron band and the density of states, we have analyzed and compared the effects of point defects and adsorbed metal atoms on the electronic properties of the hydrogen passivated 4H-SiCn0001) surface. The results show that hydrogen passivation on the surface can eliminate the additional energy level on the ideal surface. The surface defects and the adsorbed metals can introduce additional energy levels in the gap region, in which the deep level is the main energy level. The adsorption of the metal AgMoMo can increase the magnetic moment of the system. The number of additional energy levels introduced by adsorption Mo is more than that of Ag.
【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O647.3;TQ163.4

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