The heterogeneous integration of photonic integrated circuits (PICs) with a diverse range of optoelectronic materials has emerged as a transformative approach, propelling photonic chips toward larger scales, superior performance, and advanced integration levels. Notably, two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDCs), black phosphorus (BP), and hexagonal boron nitride (hBN), exhibit remarkable device performance and integration capabilities, offering promising potential for large-scale implementation in PICs. In this paper, we first present a comprehensive review of recent progress, systematically categorizing the integration of photonic circuits with 2D materials based on their types while also emphasizing their unique advantages. Then, we discuss the integration approaches of 2D materials with PICs. We also summarize the technical challenges in the heterogeneous integration of 2D materials in photonics and envision their immense potential for future applications in PICs.

中波长红外（Mid-wavelength infrared，MWIR）光电器件可用于热成像、光通信和气体传感等多个领域。二维黑磷（Black phosphorus，BP）在中波长红外范围显示出独特的优点，其所有厚度下都具有直接带隙和高迁移率的特点使其在中红外光电器件应用方面具有很大的潜力。由于皱褶的晶格结构，黑磷有较强的面内各向异性，可应用于线偏振光电器件。此外，黑磷通过掺杂、应力调控和异质堆叠等多种方式可以实现室温下中红外波段范围内的各种功能性光电器件。本文综述了黑磷的晶体和能带结构及其各向异性的光学性质，并结合近年来在偏振方向敏感的光电探测器和光谱可调控等功能性光电器件方面的应用研究进展，总结了该材料在实际应用中的主要优势和面临的重要问题。最后对二维黑磷在中红外光电器件应用领域的发展趋势进行了展望。

二维(2D)半导体材料Bi₂O₂Se由于具有独特的晶体结构与能带结构、超高的载流子迁移率和优异的稳定性，在紫外-可见-近红外光谱区的高性能电子与光电应用领域有着广阔的前景。本文综述了Bi₂O₂Se的材料制备与光学表征最新研究进展：首先，介绍了2D Bi₂O₂Se的制备方法及生长机理，包括化学气相沉积法(CVD)、湿化学工艺、分子束外延法(MBE)和脉冲激光沉积法(PLD)等；其次，介绍了其晶体结构和电子能带结构的基本性质；接下来，通过稳态光谱的研究，可以对2D Bi₂O₂Se随厚度变化的带隙等物理性质进行研究；通过研究其晶体振动模式，可进一步研究2D Bi₂O₂Se材料的缺陷形态、温度系数与热导率；此外，超快光谱技术也可以帮助研究2D Bi₂O₂Se材料内部载流子的弛豫过程与输运性能；最后，简述了当前Bi₂O₂Se研究面临的挑战与应用的前景。

Inspired by the recently predicted 2D MX₂Y₆ (M = metal element; X = Si/Ge/Sn; Y = S/Se/Te), we explore the possible applications of alkaline earth metal (using magnesium as example) in this family based on the idea of element replacement and valence electron balance. Herein, we report a new family of 2D quaternary compounds, namely MgMX₂Y₆ (M = Ti/Zr/Hf; X = Si/Ge; Y = S/Se/Te) monolayers, with superior kinetic, thermodynamic and mechanical stability. In addition, our results indicate that MgMX₂Y₆ monolayers are all indirect band gap semiconductors with band gap values ranging from 0.870 to 2.500 eV. Moreover, the band edges and optical properties of 2D MgMX₂Y₆ are suitable for constructing multifunctional optoelectronic devices. Furthermore, for comparison, the mechanical, electronic and optical properties of In₂X₂Y₆ monolayers have been discussed in detail. The success of introducing Mg into the 2D MX₂Y₆ family indicates that more potential materials, such as Ca- and Sr-based 2D MX₂Y₆ monolayers, may be discovered in the future. Therefore, this work not only broadens the existing family of 2D semiconductors, but it also provides beneficial results for the future.Inspired by the recently predicted 2D MX₂Y₆ (M = metal element; X = Si/Ge/Sn; Y = S/Se/Te), we explore the possible applications of alkaline earth metal (using magnesium as example) in this family based on the idea of element replacement and valence electron balance. Herein, we report a new family of 2D quaternary compounds, namely MgMX₂Y₆ (M = Ti/Zr/Hf; X = Si/Ge; Y = S/Se/Te) monolayers, with superior kinetic, thermodynamic and mechanical stability. In addition, our results indicate that MgMX₂Y₆ monolayers are all indirect band gap semiconductors with band gap values ranging from 0.870 to 2.500 eV. Moreover, the band edges and optical properties of 2D MgMX₂Y₆ are suitable for constructing multifunctional optoelectronic devices. Furthermore, for comparison, the mechanical, electronic and optical properties of In₂X₂Y₆ monolayers have been discussed in detail. The success of introducing Mg into the 2D MX₂Y₆ family indicates that more potential materials, such as Ca- and Sr-based 2D MX₂Y₆ monolayers, may be discovered in the future. Therefore, this work not only broadens the existing family of 2D semiconductors, but it also provides beneficial results for the future.

On-demand modification of the electronic band structures of high-mobility two-dimensional (2D) materials is of great interest for various applications that require rapid tuning of electrical and optical responses of solid-state devices. Although electrically tunable superlattice (SL) potentials have been proposed for band structure engineering of the Dirac electrons in graphene, the ultimate goal of engineering emergent quasiparticle excitations that can hybridize with light has not been achieved. We show that an extreme modulation of one-dimensional (1D) SL potentials in monolayer graphene produces ladder-like electronic energy levels near the Fermi surface, resulting in optical conductivity dominated by intersubband transitions (ISBTs). A specific and experimentally realizable platform comprising hBN-encapsulated graphene on top of a 1D periodic metagate and a second unpatterned gate is shown to produce strongly modulated electrostatic potentials. We find that Dirac electrons with large momenta perpendicular to the modulation direction are waveguided via total internal reflections off the electrostatic potential, resulting in flat subbands with nearly equispaced energy levels. The predicted ultrastrong coupling of surface plasmons to electrically controlled ISBTs is responsible for emergent polaritonic quasiparticles that can be optically probed. Our study opens an avenue for exploring emergent polaritons in 2D materials with gate-tunable electronic band structures.