Gultom Pangihutan, Hsu Chia-Chieh, Lee Min Kai, Su Shu Hsuan, Huang Jung-Chung-Andrew
Department of Physics, National Cheng Kung University, Tainan 701, Taiwan.
Instrument Division, Core Facility Center, National Cheng Kung University, Tainan 701, Taiwan.
Nanomaterials (Basel). 2024 Jan 11;14(2):157. doi: 10.3390/nano14020157.
The exploration initiated by the discovery of the topological insulator (BiSb)Te has extended to unlock the potential of quantum anomalous Hall effects (QAHEs), marking a revolutionary era for topological quantum devices, low-power electronics, and spintronic applications. In this study, we present the epitaxial growth of Cr-doped (BiSb)Te (Cr:BST) thin films via molecular beam epitaxy, incorporating various Cr doping concentrations with varying Cr/Sb ratios (0.025, 0.05, 0.075, and 0.1). High-quality crystalline of the Cr:BST thin films deposited on a c-plane sapphire substrate has been rigorously confirmed through reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) analyses. The existence of a Cr dopant has been identified with a reduction in the lattice parameter of BST from 30.53 ± 0.05 to 30.06 ± 0.04 Å confirmed by X-ray diffraction, and the valence state of Cr verified by X-ray photoemission (XPS) at binding energies of ~573.1 and ~583.5 eV. Additionally, the influence of Cr doping on lattice vibration was qualitatively examined by Raman spectroscopy, revealing a blue shift in peaks with increased Cr concentration. Surface characteristics, crucial for the functionality of topological insulators, were explored via Atomic Force Microscopy (AFM), illustrating a sevenfold reduction in surface roughness as the Cr concentration increased from 0 to 0.1. The ferromagnetic properties of Cr:BST were examined by a superconducting quantum interference device (SQUID) with a magnetic field applied in out-of-plane and in-plane directions. The Cr:BST samples exhibited a Curie temperature (T) above 50 K, accompanied by increased magnetization and coercivity with increasing Cr doping levels. The introduction of the Cr dopant induces a transition from -type ((BiSb)Te) to -type (Cr:(BiSb)Te) carriers, demonstrating a remarkable suppression of carrier density up to one order of magnitude, concurrently enhancing carrier mobility up to a factor of 5. This pivotal outcome is poised to significantly influence the development of QAHE studies and spintronic applications.
由拓扑绝缘体（BiSb）Te的发现所引发的探索已经扩展到挖掘量子反常霍尔效应（QAHE）的潜力，这标志着拓扑量子器件、低功耗电子学及自旋电子学应用的一个革命性时代。在本研究中，我们展示了通过分子束外延法生长Cr掺杂的（BiSb）Te（Cr:BST）薄膜，其中包含了不同Cr/Sb比（0.025、0.05、0.075和0.1）的各种Cr掺杂浓度。通过反射高能电子衍射（RHEED）、X射线衍射（XRD）和高分辨率透射电子显微镜（HRTEM）分析，已严格证实了沉积在c面蓝宝石衬底上的Cr:BST薄膜具有高质量的晶体结构。通过X射线衍射证实BST的晶格参数从30.53±0.05 Å减小到30.06±0.04 Å，从而确定了Cr掺杂剂的存在，并通过X射线光电子能谱（XPS）在结合能约为573.1和583.5 eV时验证了Cr的价态。此外，通过拉曼光谱定性研究了Cr掺杂对晶格振动的影响，结果表明随着Cr浓度的增加峰发生蓝移。通过原子力显微镜（AFM）探索了对拓扑绝缘体功能至关重要的表面特性，结果表明随着Cr浓度从0增加到0.1，表面粗糙度降低了七倍。通过在面外和面内方向施加磁场的超导量子干涉装置（SQUID）研究了Cr:BST的铁磁特性。Cr:BST样品表现出高于50 K的居里温度（T），并且随着Cr掺杂水平的增加，磁化强度和矫顽力也增加。Cr掺杂剂的引入导致载流子从 - 型（（BiSb）Te）转变为 - 型（Cr:（BiSb）Te），显示出载流子密度显著抑制达一个数量级，同时载流子迁移率提高达5倍。这一关键结果有望对QAHE研究和自旋电子学应用的发展产生重大影响。
