NanoLund and Department of Physics, Lund University, P.O. Box 118, 221 00 Lund, Sweden.
Department of Physics and Astronomy, Uppsala University, P.O. Box 516, 751 20 Uppsala, Sweden.
ACS Nano. 2023 Mar 14;17(5):5047-5058. doi: 10.1021/acsnano.2c12863. Epub 2023 Feb 23.
Two-dimensional (2D) topological insulators have fascinating physical properties which are promising for applications within spintronics. In order to realize spintronic devices working at room temperature, materials with a large nontrivial gap are needed. Bismuthene, a 2D layer of Bi atoms in a honeycomb structure, has recently attracted strong attention because of its record-large nontrivial gap, which is due to the strong spin-orbit coupling of Bi and the unusually strong interaction of the Bi atoms with the surface atoms of the substrate underneath. It would be a significant step forward to be able to form 2D materials with properties such as bismuthene on semiconductors such as GaAs, which has a band gap size relevant for electronics and a direct band gap for optical applications. Here, we present the successful formation of a 2D Bi honeycomb structure on GaAs, which fulfills these conditions. Bi atoms have been incorporated into a clean GaAs(111) surface, with As termination, based on Bi deposition under optimized growth conditions. Low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/S) demonstrates a well-ordered large-scale honeycomb structure, consisting of Bi atoms in a √3 × √3 30° reconstruction on GaAs(111). X-ray photoelectron spectroscopy shows that the Bi atoms of the honeycomb structure only bond to the underlying As atoms. This is supported by calculations based on density functional theory that confirm the honeycomb structure with a large Bi-As binding energy and predict Bi-induced electronic bands within the GaAs band gap that open up a gap of nontrivial topological nature. STS results support the existence of Bi-induced states within the GaAs band gap. The GaAs:Bi honeycomb layer found here has a similar structure as previously published bismuthene on SiC or on Ag, though with a significantly larger lattice constant and only weak Bi-Bi bonding. It can therefore be considered as an extreme case of bismuthene, which is fundamentally interesting. Furthermore, it has the same exciting electronic properties, opening a large nontrivial gap, which is the requirement for room-temperature spintronic applications, and it is directly integrated in GaAs, a direct band gap semiconductor with a large range of (opto)electronic devices.
二维（2D）拓扑绝缘体具有迷人的物理性质，有望在自旋电子学领域得到应用。为了实现工作在室温下的自旋电子器件，需要使用具有大非平庸能隙的材料。铋烯，一种由 Bi 原子组成的蜂窝状二维层，由于其具有创纪录的大非平庸能隙，最近引起了强烈关注，这归因于 Bi 的强自旋轨道耦合和 Bi 原子与衬底表面原子之间的异常强相互作用。如果能够在半导体（如 GaAs）上形成具有铋烯等性质的二维材料，那将是向前迈出的重要一步，因为 GaAs 具有与电子学相关的带隙大小和适用于光学应用的直接带隙。在这里，我们成功地在 GaAs 上形成了具有这些条件的二维 Bi 蜂窝结构。Bi 原子已被掺入具有 As 终止的清洁 GaAs(111)表面，基于在优化生长条件下进行的 Bi 沉积。低温扫描隧道显微镜和光谱学（LT-STM/S）证明了一个由 Bi 原子在 GaAs(111)上以 √3 × √3 30°重构组成的规则的大尺寸蜂窝结构。X 射线光电子能谱表明，蜂窝结构中的 Bi 原子仅与底层的 As 原子键合。这得到了基于密度泛函理论的计算的支持，该计算证实了具有大 Bi-As 结合能的蜂窝结构，并预测了 GaAs 带隙内开启非平庸拓扑性质的间隙的 Bi 诱导能带。STS 结果支持 GaAs 带隙内存在 Bi 诱导态。这里发现的 GaAs:Bi 蜂窝层与之前在 SiC 或 Ag 上发表的铋烯具有相似的结构，尽管晶格常数明显更大，且 Bi-Bi 键合较弱。因此，它可以被认为是铋烯的一个极端情况，这从根本上是有趣的。此外，它具有相同令人兴奋的电子特性，开启了一个大的非平庸间隙，这是室温自旋电子学应用的要求，并且它直接集成在 GaAs 中，GaAs 是一种具有广泛（光电）器件的直接带隙半导体。
