GaN基稀磁半导体薄膜的制备与性能研究

发布时间：2018-05-30 04:38

本文选题：LMBE + GaMnN　；参考：《山东师范大学》2014年博士论文

【摘要】：随着半导体技术的发展，半导体芯片中晶体管的特征尺寸从十几年前的0.35μm缩小为目前最先进的22nm，这使得芯片的集成度提高了成千上万倍，同时芯片中晶体管器件之间的绝缘层的厚度也在不断地减小。进一步发展下去，当缘层的厚度减小到一定程度将会出现量子隧道效应从而导致绝缘层失效，进而会导致整个集成电路无法工作。此外，光刻工艺也是半导体技术发展的一个主要瓶颈。总之，半导体芯片中晶体管的特征尺寸不可能无限减小，其发展空间已经十分有限，要进一步提高芯片的集成度和性能就必须寻找新的出路。近年来发展起来的自旋电子学有望同时利用稀磁半导体（DMS）材料中电子的电荷和自旋两个自由度，从而为芯片集成度的提高和电路性能的提升提供了广阔的空间。在稀磁半导体中，由于磁性离子固有的磁矩与能带中电子自旋之间存在耦合交换作用，从而导致了许多新奇的物理现象，例如磁致绝缘体-金属转变、反常霍尔效应、束缚磁极化子、巨塞曼分裂、巨法拉第效应和负磁阻效应等。这些新奇的物理特性为一些新技术的发展提供了条件，使其在磁感应器、高密度非易失性存储器、光隔离器、半导体激光器和自旋量子计算机等领域有广阔的应用前景。因此，稀磁半导体材料受到了各国科学家的关注，成为近年来的研究热点。要研制实用化的自旋电子器件就必须制备出能在室温下具有铁磁性并能与现有半导体器件制造工艺相兼容的新型稀磁半导体材料，这也是目前的研究重点。自从2000年Science杂志报道了以GaMnN为代表的GaN基稀磁半导体材料的居里温度可能达到室温以上，很多研究小组对GaN基稀磁半导体材料进行了大量的研究并取得了一定的进展。但是，由于所用的实验设备、生长条件、处理工艺以及掺杂元素的种类和数量等条件都不尽相同，所以实验结果很分散。即使是同一种材料，不同研究小组报道的结果也有很大差异，甚至得出相反的结论。对稀磁半导体材料铁磁性的起源问题还存在争议。本文在多种实验条件下进行了大量的研究，期望找到最佳实验条件制备出理想的GaMnN稀磁半导体材料。AlGaN材料也是GaN系列材料的一种，以GaN/AlGaN异质节为基础的高迁移率晶体管在超高频、耐高温和大功率器件领域有着很多潜在的应用。本文研究了稀土金属Tb掺杂的GaN和AlGaN材料的各种性质，以及Cr和Sm共同掺杂的AlGaN材料，希望在提高居里温度以及实现磁性可控方面有所突破。主要研究成果如下： 1.用LMBE方法在蓝宝石衬底上成功制备了居里温度高达340K的GaMnN稀磁半导体薄膜。N2压强对薄膜的性质有很大的影响，随着N2压强从7.0Pa减小到0.75Pa，薄膜的结晶质量变好了，晶粒尺寸变大了，同时样品的饱和磁化强度（Ms）也增强了。当N2压强进一步减小到0.15Pa时，薄膜的结晶质量变差了，晶粒尺寸变小了并伴随着龟裂纹，同时样品的Ms也减弱了。从我们的实验结果看，制备GaMnN稀磁半导体薄膜的最佳N2压强为0.75Pa。在样品生长的过程中通过调节N2压强，就可以生长出具有特定磁性的GaMnN薄膜。 2.退火处理工艺对GaMnN薄膜的性质有很重的影响。未经过退火处理的样品的结晶质量很差属于非晶GaMnN薄膜。随着退火时间从5min增加到25min，样品的结晶质量逐渐提高。然而，过长的退火时间又会导致样品的结晶质量变差，我们的实验结果表明，在1000℃下最佳退火时间为25min。我们制备的GaMnN薄膜样品中Mn离子既有+2价也有+3价，而它们的比例也随退火时间的变化而变化，这对磁性有很重要的影响。可以通过控制退火时间使样品具有较好的结晶质量，同时具有特定的磁性。 3.离子注入过程会对晶格造成损伤，导致薄膜的结晶质量变差。退火处理工艺可以部分地修复晶格的损伤，但与原生样品相比晶格略有膨胀。GaN:Tb和AlGaN:Tb两种样品在室温下都表现出了铁磁性，这可以用束缚极化子（BMP）理论来解释。与GaN:Tb相比，AlGaN:Tb样品中的原子平均饱和磁矩数值几乎是GaN:Tb样品中的两倍，我们推断AlGaN:Tb样品中的Al原子会对整个样品的总磁矩造成影响，这还需要进一步研究论证。 4.在室温下，，Cr和Sm共掺杂的AlGaN样品呈现出铁磁性并且存在巨磁矩效应，特别是在900℃下退火处理的样品的巨磁矩效应更加明显。巨磁矩效应可能来源于两个方面：一个是Cr3+离子和Sm3+离子之间3d-4f耦合，另一个是AlGaN晶格中的Cr3+-BMP和Sm3+-BMP之间的耦合，也可能两者都有。我们的研究表明，可以通过调节在AlGaN薄膜中掺杂的Cr离子和Sm离子的数量以及比例来调节薄膜的磁性。
[Abstract]:With the development of semiconductor technology, the characteristic size of transistors in semiconductor chips has been reduced from 0.35 mu m to the most advanced 22nm at present. This makes the chip's integration increased thousands of times, and the thickness of the insulating layer between transistors in the chip is also decreasing. Further development, when the edge layer is thick. A certain degree will reduce to a certain extent, the quantum tunneling effect will lead to the failure of the insulating layer, which will lead to the failure of the entire integrated circuit. In addition, the lithography process is also a major bottleneck in the development of semiconductor technology. In a word, the characteristic size of transistors in semiconductor chips can not be reduced infinitely, and the development space has been very useful. In order to further improve the integration and performance of chips, we must find new ways.
In recent years, the development of spintronics is expected to make use of the two degrees of freedom of electron charge and spin in the thin magnetic semiconductor (DMS) material, which provides a broad space for the enhancement of the chip integration and the improvement of the circuit performance. In dilute magnetic semiconductors, the existence of the intrinsic magnetic moments of the magnetic separation and the electron spin in the energy band exists in the dilute magnetic semiconductor. Coupling exchange, resulting in many new physical phenomena, such as magnetic insulator metal transition, anomalous Holzer effect, bound magnetopolaron, giant Zeeman splitting, giant Faraday effect and negative magnetoresistance effect. These new physical properties provide conditions for the development of some new technologies to make it in magnetic sensors, high density and non easy. There is a wide range of applications in the fields of loss of memory, optical isolator, semiconductor laser and spin quantum computer. Therefore, thin magnetic semiconductor materials have attracted the attention of scientists from all countries and become a hot spot of research in recent years. To develop practical spin electronic devices, it is necessary to produce ferromagnetic and can be available at room temperature. New thin magnetic semiconductor materials, which are compatible with semiconductor manufacturing processes, are also the focus of current research. Since 2000, Science magazine reported that the Curie temperature of GaN based dilute magnetic semiconductors, represented by GaMnN, may reach room temperature. Many research teams have done a lot of research on GaN Based Diluted Magnetic Semiconductor Materials. Some progress has been made. However, as the experimental equipment, the growth conditions, the processing technology and the variety and quantity of the doped elements are different, the experimental results are very scattered. Even the same material, the results of the different research groups are very different, and even the opposite conclusion is reached. The issue of the origin of ferromagnetism is still controversial.
In this paper, a lot of studies have been carried out in various experimental conditions. It is expected to find the best experimental conditions to prepare the ideal GaMnN thin magnetic semiconductor material.AlGaN material as well as a kind of GaN series. The high mobility transistor based on GaN/AlGaN heterojunction has many potential applications in the field of UHF, high temperature and high power devices. The properties of GaN and AlGaN doped with rare earth metal Tb and the Co doped AlGaN materials of Cr and Sm are studied in this paper. It is hoped that there are some breakthroughs in improving the Curie temperature and magnetic controllability. The main research results are as follows:
1. the.N2 pressure of GaMnN thin magnetic semiconductor thin film with Curie temperature up to 340K was successfully prepared by LMBE method on the sapphire substrate. The properties of the thin film were greatly influenced by the.N2 pressure of the thin film. With the decrease of the N2 pressure from 7.0Pa to 0.75Pa, the crystalline quality of the film became better, the grain size became larger, and the saturation magnetization (Ms) of the sample was also enhanced. When N2 pressure was pressed. When the intensity is further reduced to 0.15Pa, the crystalline quality of the film becomes worse, the grain size becomes smaller and the tortoise crack is accompanied by the Ms. From our experimental results, the optimum N2 pressure of the preparation of GaMnN thin magnetic semiconductor thin film is that 0.75Pa. can grow by adjusting the N2 pressure in the process of sample growth. Magnetic GaMnN film.
2. annealing process has a very heavy effect on the properties of GaMnN films. The crystalline quality of the samples without annealing is very poor in the amorphous GaMnN film. As the annealing time increases from 5min to 25min, the crystal quality of the samples increases gradually. However, the long annealing time will lead to the deterioration of the crystal quality of the sample, our experimental knot. The results show that the optimum annealing time at 1000 C is 25min.. The Mn ions in the samples of GaMnN films have both +2 valence and +3 valence, and their proportion also varies with the change of annealing time, which has a very important influence on the magnetic properties.
The 3. ion implantation process can cause damage to the crystal lattice, resulting in the deterioration of the crystalline quality of the film. The annealing process can partially repair the damage of the lattice, but compared with the original sample, two samples of.GaN:Tb and AlGaN:Tb exhibit ferromagnetism at room temperature, which can be explained by the theory of bound polaron (BMP). And GaN:T Compared with B, the average atomic saturation magnetic moment in the AlGaN:Tb sample is almost two times that of the GaN:Tb sample. We infer that the Al atom in the AlGaN:Tb sample will affect the total magnetic moment of the whole sample, which needs further study.
4. at room temperature, the AlGaN samples Co doped by Cr and Sm present ferromagnetism and have giant magnetic moment effect, especially the giant magnetic moment effect of the samples annealed at 900 C. The giant magnetic moment effect may come from two aspects: one is the 3d-4f coupling between the Cr3+ ion and the Sm3+ ion, the other is Cr3+-BMP in the AlGaN lattice and the other is the Cr3+-BMP in the AlGaN lattice and the other is the Cr3+-BMP and the Cr3+-BMP in the AlGaN lattice. The coupling between Sm3+-BMP may also have both. Our study shows that the magnetic properties of the films can be adjusted by regulating the number and proportion of the Cr ions and Sm ions doped in the AlGaN film.
【学位授予单位】：山东师范大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O484.1

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