【摘要】：SiC表面重構(gòu)的發(fā)生會(huì)引起表面態(tài)密度增加,這使得SiC材料表面的電學(xué)、光學(xué)等特性不同于體內(nèi)的原子,極大地影響了 SiC功率器件的性能。因此本課題基于Valence-Mending概念對(duì)4H/6H/3C-SiC重構(gòu)表面進(jìn)行了 S吸附計(jì)算,希望得到解開SiC重構(gòu)表面的理論模型與方法,從而為實(shí)驗(yàn)驗(yàn)證提供更好的理論依據(jù),最終達(dá)到改善器件穩(wěn)定性的目的。本課題主要采用第一性原理計(jì)算,從吸附能、鍵長(zhǎng)、鍵角的恢復(fù)能力、態(tài)密度、成鍵布居以及電荷布居分析等方面,對(duì)4H/6H/3C-SiC重構(gòu)表面分別進(jìn)行了 S原子的吸附分析,并對(duì)Si材料(2x1)重構(gòu)表面分別進(jìn)行了H、C、O、S、Se 五種原了的吸附比較,進(jìn)而分析表面重構(gòu)結(jié)構(gòu)由于外來(lái)原子的引入而向體結(jié)構(gòu)恢復(fù)的程度,探索S吸附對(duì)器件特性的改善情況。主要結(jié)論如下:1.吸附S原子后重構(gòu)體系的表面能都會(huì)不同程度的降低,結(jié)構(gòu)趨于穩(wěn)定,表面態(tài)數(shù)量下降,S原子與重構(gòu)鍵發(fā)生作用,重構(gòu)結(jié)構(gòu)有向體結(jié)構(gòu)恢復(fù)的趨勢(shì),這與本課題小組在實(shí)驗(yàn)方面的結(jié)果相吻合。2.對(duì)不同初始吸附位和不同覆蓋率下的SiC不同重構(gòu)表面進(jìn)行S原子的吸附對(duì)比,結(jié)果發(fā)現(xiàn),4H/6H-SiC表面兩種重構(gòu)結(jié)構(gòu)的最佳初始吸附位是TOP位,((?)×(?))R30°(以下簡(jiǎn)稱(?))重構(gòu)和(3x3)重構(gòu)的最佳吸附率分別是1/2ML和1/3ML。3C-SiC表面(3x2)重構(gòu)的最佳初始吸附位是H3位,最佳吸附率是11/6ML; (2x1)重構(gòu)的最佳初始吸附位是B位,最佳吸附率是1/2MIL。3.吸附的S原了解開表面重構(gòu)鍵的能力對(duì)不同重構(gòu)結(jié)構(gòu)是不一樣的。其中4H-SiC重構(gòu)表面的鍵長(zhǎng)、鍵角恢復(fù)程度比6H-SiC稍大;相比于(3x3)重構(gòu),(?)重構(gòu)的鍵角恢復(fù)更明顯,吸附能更低,結(jié)構(gòu)更穩(wěn)定,S原子對(duì)(?)亟構(gòu)結(jié)構(gòu)的恢復(fù)影響更大。而3C-SiC表面重構(gòu)鍵的恢復(fù)較之4H/6H-SiC更明顯;相比于(3x2)重構(gòu),(2x1)重構(gòu)的吸附能更低,結(jié)構(gòu)更穩(wěn)定,鍵長(zhǎng):、鍵角的恢復(fù)程度稍高,S吸附對(duì)(2x1)重構(gòu)面的解重構(gòu)貢獻(xiàn)要大些。4.吸附S原子后,4H/6H/3C-SiC表面重構(gòu)結(jié)構(gòu)均有向體結(jié)構(gòu)恢復(fù)的趨勢(shì),但恢復(fù)能力不同。其中4H-SiC表面重構(gòu)結(jié)構(gòu)的恢復(fù)程度比6H-SiC稍大,而3C-SiC的重構(gòu)表面受S原子的影響最大,重構(gòu)結(jié)構(gòu)恢復(fù)最為理想,同時(shí)立方結(jié)構(gòu)體系的表面吸附能相對(duì)較小,表面穩(wěn)定性更強(qiáng)。5.對(duì)Si表面(2x1)重構(gòu)結(jié)構(gòu)分別進(jìn)行了 H、C、O、S、Se五種原子的吸附比較,發(fā)現(xiàn)吸附原子均有向最穩(wěn)定的吸附位置B位移動(dòng)的趨勢(shì),表面非對(duì)稱的硅硅二聚物由于外來(lái)原子的引入變成了對(duì)稱結(jié)構(gòu),且不同吸附原子對(duì)應(yīng)的重構(gòu)表面鍵長(zhǎng)、鍵角恢復(fù)能力相差較大。對(duì)于吸附原子H、C、O、S、Se來(lái)說(shuō),鍵角的最高恢復(fù)率分別是18%、19%、21%、51%、20%,故當(dāng)吸附原子為S且吸附率為1/2ML下的B位吸附時(shí),表面重構(gòu)結(jié)構(gòu)的鍵角恢復(fù)程度最大。
[Abstract]:The occurrence of SiC surface reconstruction will increase the density of states on the surface, which makes the surface electrical and optical properties of SiC materials different from the atoms in the body, which greatly affects the performance of SiC power devices. Therefore, based on the concept of Valence-Mending, the S adsorption calculation of the reconstructed surface of 4H/6H/3C-SiC is carried out in order to obtain the theoretical model and method of unraveling the reconstructed surface of SiC, so as to provide a better theoretical basis for experimental verification. Finally, the stability of the device is improved. In this paper, the adsorption of S atoms on the reconstructed surface of 4H/6H/3C-SiC was carried out from the aspects of adsorption energy, bond length, recovery ability of bond angle, density of states, bonding population and charge population analysis. The adsorption of the reconstructed surface of Si material (2x1) was compared with that of the original five kinds of se, and then the degree of the surface reconstruction structure being restored to the bulk structure due to the introduction of foreign atoms was analyzed, and the improvement of the characteristics of the device by the adsorption of S was explored. The main conclusions are as follows: 1. The surface energy of the reconstructed system decreases in varying degrees after the adsorption of S atoms, the structure tends to be stable, the number of surface states decreases, the S atoms interact with the reconstructed bond, and the reconstructed structure tends to recover. This is consistent with the experimental results of our team. 2. The adsorption of S atoms on different reconstructed surfaces of SiC with different initial adsorption sites and different coverage was compared. It was found that the best initial adsorption sites for the two reconstructed structures on 4H/6H-SiC surface were, (? 脳 (?) R30 擄(hereinafter referred to as (?). The optimal adsorption rates of (3x3) and (3x3) reconstruction are H3 sites for 1/2ML and 1/3ML.3C-SiC surface (3x2) reconstructions, and 11 / 6MLfor (2x1) reconstruction, respectively, and B sites for (2x1) reconstruction, and 1 / 2MIL.3for (2x1) reconstruction, respectively. The ability of the adsorbed S to unravel the surface remodeling bond is different for different reconstructed structures. The bond length of the reconstructed surface of 4H-SiC is slightly larger than that of 6H-SiC, and compared with that of (3x3), (?) The reconstructed bond angle is more obvious, the adsorption energy is lower, the structure is more stable, and the S atom pair (?) The restoration of the structure is more important. Compared with (3x2) reconstruction, the adsorption energy of (2x1) remodeling is lower, the structure is more stable, the bond length is higher: the bond angle is a little higher, and S adsorption contributes more to the (2x1) reconstruction surface. After the adsorption of S atom, the reconstructed structure of 4H/6H/3C-SiC surface has the tendency of body structure recovery, but the recovery ability is different. The recovery degree of surface reconstructed structure of 4H-SiC is slightly larger than that of 6H-SiC, while the reconstructed surface of 3C-SiC is most affected by S atom, and the reconstructed structure is most ideal. Meanwhile, the surface adsorption energy of cubic structure system is relatively small and the surface stability is stronger than that of cubic structure system. The adsorption of the reconstructed structure of the Si surface (2x1) was compared with that of the five kinds of atoms. It was found that the adsorption atoms were moving towards the most stable adsorption sites. The silicon dimer with asymmetric surface changes into a symmetrical structure due to the introduction of foreign atoms, and the reconstructed surface bond length corresponding to different adsorption atoms has a large difference in bond angle recovery ability. The highest recovery rate of the bond angle for the adsorbed atom is 18, respectively. Therefore, when the adsorption atom is S and the adsorption rate is B site adsorption rate of 1/2ML, the recovery degree of the bond angle of the reconstructed surface structure is the greatest.
【學(xué)位授予單位】：西安理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TN304.24

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