层状α-GaGeTe晶体及其少层薄膜的物性研究

自石墨烯于2004 年被发现以来，二维（2D）材料在材料科学、纳米技术以及量子研究领域带来了革命性的变化。这类材料因其独特的物理特性（高电子迁移率、优异的光学性质、高强度和高弹性模量等优势）和丰富的化学性质（高表面积比、优异的催化性能和光化学活性等）而受到广泛的关注。特别是在量子物理方面，2D 材料为研究量子限域效应引起的电子结构变化、非平庸的拓扑属性及非常规的超导属性等物理性质提供了新的研究平台。GaGeTe 作为2D 材料家族中的一种，其块材被预测可能表现出非平庸的拓扑态，其少层薄膜的能带结构易受到层数、外加电场、磁场以及应力等多种内外部因素的显著影响，展现出极其丰富的物理特性。不仅如此，研究者们验证了GaGeTe 的多数载流子为空穴且在空气中较稳定，这在已知的2D 材料中相对罕见。然而，关于少层GaGeTe 薄膜的能带结构随层数变化的问题，科学界仍存在争议。探测GaGeTe 薄膜光学信号的过程中激光或加热可能对GaGeTe 造成损伤，导致缺乏对其本征光学信号（如拉曼光谱）的实验分析。因此，本论文将重点研究GaGeTe 晶体及其少层2D 形态的本征物理特性。

本论文首先通过布里奇曼方法获得高质量的GaGeTe 单晶，并通过改良剥离方法获得少层甚至单层的GaGeTe 薄膜样品。通过改进实验方法，我们先后获得了GaGeTe 薄膜的本征光学衬度谱、拉曼光谱和电输运特性。研究结果显示，GaGeTe的光学衬度谱和拉曼光谱显著依赖于薄膜的层数，且通过角分辨偏振拉曼光谱的探测，我们确认了GaGeTe 薄膜具有明显的各向异性。不仅如此，300 nm SiO₂/Si衬底上的少层GaGeTe 薄膜的光学衬度谱在550 nm 以及600-700 nm 波段有明显的衬度峰，因此通过绿光和红光波段的滤波片观察少层GaGeTe 薄膜更明显，这一结果与理论计算结果相似。基于这些结果，本论文开发了使用MATLAB 的图像分析技术，对少层GaGeTe 的明场及暗场成像中红色（R）、绿色（G）和蓝色（B）通道的衬度值进行分析，发展了一种适用于多种2D 薄膜材料的低损伤的光学厚度分析方法。此外，本论文还通过电学测量发现GaGeTe 薄膜材料在低温小磁场条件下表现出负磁阻现象和弱局域效应。因此，本论文的研究结果不仅揭示了本征的GaGeTe 薄膜在光电器件和微电子领域的潜在应用潜力，还为其他2D 材料的研究以及高性能器件应用的开发提供了有力的技术支持和研究基础。

Since the discovery of graphene in 2004, two-dimensional (2D) materials have revolutionized materials science, nanotechnology, and quantum research. These materials attract attention due to their wide distribution, unique physical properties (Combining the advantages of high electron mobility, desirable optical properties, high strength, and high elastic modulus.), and rich chemical properties (Including high surface area to volume ratio, excellent catalytic performance, and photochemical activity, among others.). In quantum physics, 2D materials provide a new platform for studying changes in electronic structure due to quantum confinement, non-trivial topological properties, and unconventional superconductivity. GaGeTe, a member of the 2D material family, is predicted to exhibit non-trivial topological states in its bulk form, and the band structures of its fewlayer films are significantly influenced by factors such as layer number, applied electric fields, magnetic fields, and stress, displaying a range of physical properties. Furthermore, researchers verified that the main carriers of GaGeTe are holes and GaGeTe films are stable in air, which is relatively rare in known 2D materials. GaGeTe has been verified to exhibit stable p-type characteristics, which are rare in 2D materials. However, the band structure of GaGeTe films with varying layers remains controversial, and the analysis of optical and electrical signals due to layer number changes is incomplete. Experimental analyses of intrinsic optical signals (such as Raman spectroscopy) are lacking due to damage from lasers or heating during detection. This thesis will focus on the intrinsic physical properties of GaGeTe crystals and their few-layer 2D forms.

In this thesis, high-quality GaGeTe single crystals were obtained using the Bridgman
method, and few-layer or even monolayer GaGeTe film samples were acquired through improved exfoliation techniques. By refining experimental methods, we obtained the intrinsic optical contrast spectroscopy, Raman spectroscopy, and electrical transport properties of GaGeTe films. Our research indicates that GaGeTe’s optical contrast and Raman spectra are strongly layer-dependent, and angle-resolved polarized Raman spectroscopy has revealed significant anisotropy in the film. Additionally, the optical contrast spectroscopy of GaGeTe films on 300 nm SiO₂/Si substrates exhibited distinct contrast peaks at 550 nm and 600-700 nm, making the films more visible under green and red light filters, which is consistent with the theoretical calculations. Based on these results, we developed an image analysis technique using MATLAB to analyze the red (R), green (G), and blue (B) channel contrast values in bright and dark field imaging of GaGeTe films, creating a non-destructive thickness analysis method for various 2D materials. Moreover, electrical measurements revealed that GaGeTe films exhibit negative magnetoresistance and weak localization effects under low temperature and small magnetic field conditions. The findings of this thesis not only highlight the potential applications of GaGeTe films in optoelectronic devices and microelectronics but also provide strong technical support and a research foundation for the study of other 2D materials and the development of high-performance device applications.

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