掺杂InN薄膜的输运性质与磁学性质研究

发布时间：2018-08-17 17:01

【摘要】：半导体器件与半导体材料自身的物理性质有着密切的依赖关系。近些年,人们对Ⅲ-Ⅴ主族半导体表现出浓厚的兴趣。其中,InN在第三主族氮化物半导体中具有最低的有效电子质量,这意味着InN具有高迁移率和高饱和速率,引起广泛关注。随着分子束外延等薄膜生长技术的发展,获得的高质量InN表现出较窄的能隙,约0.6 eV,在In1-xGaxN固溶体中通过改变Ga的含量就可以使其能隙覆盖从近红外到紫外的波段,在光发射二极管中有很好的应用价值,成为重要的光电器件材料。由于材料带隙与通信光纤的波长相当,高质量InN或固溶体可应用于高速长途通讯,在光通信方面有重要应用前景。然而由于生长InN不可避免引入大量N空位,具有强烈的自补偿效应,InN总表现为n型半导体,使得研制P-型InN成为一个难题。论文围绕高质量InN薄膜,利用非平衡离子注入技术,在理论设计的基础上尝试通过Mg,Ba,Zn,Mn掺杂和应力调控向材料中引入受主型缺陷和其他本征缺陷,成功报道了 InN:Ba和InN:Zn的p型传导,成为国际上继Mg表面掺杂形成p型导电的又两个p-InN的案例;除此之外,还报道了 InN中的超导电性和由掺杂、应力分别诱发的铁磁性,发现掺杂InN中超导和铁磁性共存;最后,工作还延伸到极性对氧化物薄膜的调控行为,测得并解释了 SrRu03(1 11)薄膜表面的重构现象,为氧化物相关异质结的研究奠定基础。主要研究包括:1)在两个掺杂InN体系中获得了的p型导电性。InN中的In为+3价,根据半导体掺杂理论,当体系中掺杂+2价的离子时,可以产生替位缺陷,在带隙中产生受主型能级,进而可能得到由空穴为主要载流子的半导体系统。然而由于InN稳定费米能级在导带,体系存在严重的自补偿现象,很难实现空穴掺杂。我们利用第一性原理计算普遍搜寻具有+2价掺杂的离子,发现Mg,Sr,Zn,Mn,Ba等有望成为受主杂质。考虑到这些离子的平衡掺杂的困难,我们提出通过离子注入技术实现非平衡掺杂,获得成功。我们通过离子注入对InN先后进行Ba离子和Zn离子的掺杂,研究它们对InN传导性质的影响。对于InN:Ba薄膜,X射线衍射及掠入射结果表明Ba掺杂成功引入了替位型缺陷。随着掺杂浓度的增加,InN:Ba薄膜的光致发光谱逐渐减弱直至消失,这是由于材料的主体层中存在空穴,表面电子聚集层与其之间存在电势差,阻止光生载流子的复合。另外,霍尔迁移率随着温度先减小又增大的行为也可以判定薄膜是由表面电子聚集层和p型主体层组成。对于InN:Zn薄膜,霍尔系数在低温处是正值,随着温度升高变为负值。霍尔系数符号的变化表明体系中电子和空穴载流子同时存在。温度变化会影响本征载流子的浓度,因此体系会在空穴和电子分别作为主要载流子的状态之间转变。2)获得了基于InN体系的低温超导电行为和铁磁性。研究发现InN和InN:Zn薄膜在3.8 K附近发生了由正常态向超导态的转变。这种超导电性很可能来自于面内的最近邻In原子之间的相互作用。对比以上两种材料,Zn离子掺杂引入的缺陷对磁涡旋线有钉扎作用,从而使得InN:Zn表现出更强的迈斯纳效应。激活能与磁场之间关系的拟合结果,与超导性质来自于二维In原子相互作用的理论一致。研究InN:Zn的迈斯纳效应时,我们发现磁滞回线不仅显示出抗磁性,还有铁磁背景。由于Zn最外层电子只有两个电子,使得掺杂后材料中N原子p轨道没有达到全满,根据洪特定则,p轨道上的电子会出现自旋极化。当这种自旋极化之间出现相互关联时,便可以形成磁长程有序。此外,半导体中的铁磁性还可以来自于其本征缺陷。由于A1203与InN之间有很大晶格失配,直接在A1203上生长InN可以引入In空位本征缺陷。实验和理论研究都表明,由晶格失配导致的In空位会使得InN薄膜表现出铁磁性。3)获得SrRu03(1 11)薄膜(?)×(?)表面重构。SrRu03是一种巡游铁磁性钙钛矿氧化物,其磁性和导电性与薄膜厚度、生长质量及取向相关联,外延SrRu03(111)薄膜具有最强磁性,这一结果引起了人们的极大兴趣。利用脉冲激光沉积,我们生长出高质量的SrRuO3(111)薄膜,并发现薄膜表面出现重构现象。利用角分辨X射线光电子谱,我们分析了薄膜表面原子排布情况,发现重构是来自于有序的氧空位。对薄膜在强氧化性环境下退火可以去除表面重构,进一步在真空下退火,这种重构再次出现。钙钛矿在[111]方向上表现出很强的极性,为了降低表面极性能,原子会自发弛豫或者发生重构。该结果对于基于SrRu03(111)的异质结研究有借鉴意义。
[Abstract]:Semiconductor devices have a close dependence on the physical properties of semiconductor materials. In recent years, people have shown great interest in III-V primary semiconductors. InN has the lowest effective electron mass in third-group nitride semiconductors, which means that InN has a high mobility and high saturation rate, and attracts wide attention. With the development of thin film growth technology such as molecular beam epitaxy, the obtained high quality InN exhibits narrow energy gap, about 0.6 eV. In In1-xGaxN solid solution, the gap can be covered from near infrared to ultraviolet by changing the content of Ga. It has a good application value in photodiodes and becomes an important optoelectronic device material. High-quality InN or solid solution can be used in high-speed and long-distance communication because the band gap of material is equal to the wavelength of communication fiber. It has important application prospects in optical communication. Around the high quality InN thin films, the acceptor-type defects and other intrinsic defects were introduced into the materials through Mg, Ba, Zn, Mn doping and stress regulation on the basis of theoretical design by using non-equilibrium ion implantation technology. The p-type conduction of InN: Ba and InN: Zn was successfully reported, which became the two p-InN doped on the surface of Mg and formed the p-type conduction. In addition, the superconductivity in InN and the ferromagnetism induced by doping and stress are also reported. It is found that superconductivity and ferromagnetism coexist in doped InN. Finally, the work extends to the regulation behavior of polarity on oxide films, and the surface reconstruction of SrRu03 (111) films is measured and explained, which is the study of oxide-related heterojunctions. The main research contents are as follows: 1) P-type conductivity in two doped InN systems is obtained. In InN is + 3 valence. According to the theory of semiconductor doping, when ions with + 2 valence are doped in the system, substitution defects can be produced, acceptor-type energy levels can be produced in the band gap, and then the semiconductor system with hole as the main carrier can be obtained. However, it is difficult to realize hole doping due to the serious self-compensation of InN stable Fermi level in the conduction band. We use the first-principles calculation to search for ions with +2 valence doping and find that Mg, Sr, Zn, Mn, Ba and so on are expected to become acceptor impurities. In the case of InN:Ba thin films, X-ray diffraction and grazing incidence show that the substitution defect is successfully induced by Ba doping. With the increase of doping concentration, the photoinduced properties of InN:Ba thin films are studied. The luminescence spectrum gradually weakens and disappears due to the existence of holes in the main layer of the material and the potential difference between the surface electron aggregation layer and the surface electron aggregation layer, which prevents the recombination of photogenerated carriers. NN:Zn thin films have a positive Hall coefficient at low temperatures and a negative Hall coefficient as the temperature increases. The change of Hall coefficient symbols indicates that both electron and hole carriers exist in the system. The superconductivity of InN and InN:Zn thin films at low temperatures and their ferromagnetism have been investigated. It is found that the transition from normal state to superconducting state takes place near 3.8 K. This superconductivity is probably due to the interaction between the nearest in-plane atoms. Compared with the above two materials, the defects introduced by Zn ion doping pin the magnetic vortex lines. In the study of the Meissner effect of InN:Zn, we found that the hysteresis loops not only exhibit diamagnetism, but also ferromagnetic background. There are two electrons that make the p orbital of N atom in the doped material not completely full. According to Hund's rule, the electrons in the p orbital will appear spin polarization. When the spin polarization is correlated with each other, the magnetic long range order can be formed. In addition, the ferromagnetism in semiconductors can also come from its intrinsic defect. There is a large lattice mismatch between InN and SrRu03, and the growth of InN directly on A1203 can introduce in-vacancy intrinsic defects. Both experimental and theoretical studies show that in-vacancy caused by lattice mismatch can make InN films show ferromagnetism. Epitaxial SrRu03 (111) thin films have the strongest magnetism, which is related to the film thickness, growth quality and orientation. This result has aroused great interest. High quality SrRuO3 (111) thin films have been grown by pulsed laser deposition and surface reconstruction has been found. Thin films have been analyzed by angular resolution X-ray photoelectron spectroscopy. It is found that the reconstructions are due to the ordered oxygen vacancies on the surface of the films. Annealing the films in strong oxidizing environment can remove the surface reconstructions and further annealing in vacuum, the reconstructions occur again. Perovskite shows a strong polarity in the [111] direction. In order to reduce the surface polarity, the atoms will relax or spontaneously occur. The results are useful for the study of heterojunction based on SrRu03 (111).
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O484

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