S吸附对SiC表面重构影响的第一性原理研究
发布时间：2018-10-15 17:11
【摘要】：SiC表面重构的发生会引起表面态密度增加,这使得SiC材料表面的电学、光学等特性不同于体内的原子,极大地影响了 SiC功率器件的性能。因此本课题基于Valence-Mending概念对4H/6H/3C-SiC重构表面进行了 S吸附计算,希望得到解开SiC重构表面的理论模型与方法,从而为实验验证提供更好的理论依据,最终达到改善器件稳定性的目的。本课题主要采用第一性原理计算,从吸附能、键长、键角的恢复能力、态密度、成键布居以及电荷布居分析等方面,对4H/6H/3C-SiC重构表面分别进行了 S原子的吸附分析,并对Si材料(2x1)重构表面分别进行了H、C、O、S、Se 五种原了的吸附比较,进而分析表面重构结构由于外来原子的引入而向体结构恢复的程度,探索S吸附对器件特性的改善情况。主要结论如下:1.吸附S原子后重构体系的表面能都会不同程度的降低,结构趋于稳定,表面态数量下降,S原子与重构键发生作用,重构结构有向体结构恢复的趋势,这与本课题小组在实验方面的结果相吻合。2.对不同初始吸附位和不同覆盖率下的SiC不同重构表面进行S原子的吸附对比,结果发现,4H/6H-SiC表面两种重构结构的最佳初始吸附位是TOP位,((?)×(?))R30°(以下简称(?))重构和(3x3)重构的最佳吸附率分别是1/2ML和1/3ML。3C-SiC表面(3x2)重构的最佳初始吸附位是H3位,最佳吸附率是11/6ML; (2x1)重构的最佳初始吸附位是B位,最佳吸附率是1/2MIL。3.吸附的S原了解开表面重构键的能力对不同重构结构是不一样的。其中4H-SiC重构表面的键长、键角恢复程度比6H-SiC稍大;相比于(3x3)重构,(?)重构的键角恢复更明显,吸附能更低,结构更稳定,S原子对(?)亟构结构的恢复影响更大。而3C-SiC表面重构键的恢复较之4H/6H-SiC更明显;相比于(3x2)重构,(2x1)重构的吸附能更低,结构更稳定,键长:、键角的恢复程度稍高,S吸附对(2x1)重构面的解重构贡献要大些。4.吸附S原子后,4H/6H/3C-SiC表面重构结构均有向体结构恢复的趋势,但恢复能力不同。其中4H-SiC表面重构结构的恢复程度比6H-SiC稍大,而3C-SiC的重构表面受S原子的影响最大,重构结构恢复最为理想,同时立方结构体系的表面吸附能相对较小,表面稳定性更强。5.对Si表面(2x1)重构结构分别进行了 H、C、O、S、Se五种原子的吸附比较,发现吸附原子均有向最稳定的吸附位置B位移动的趋势,表面非对称的硅硅二聚物由于外来原子的引入变成了对称结构,且不同吸附原子对应的重构表面键长、键角恢复能力相差较大。对于吸附原子H、C、O、S、Se来说,键角的最高恢复率分别是18%、19%、21%、51%、20%,故当吸附原子为S且吸附率为1/2ML下的B位吸附时,表面重构结构的键角恢复程度最大。
[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 掳(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.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304.24
本文编号：2273231
[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 掳(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.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304.24
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