Zhang Guowei, Chaves Andrey, Huang Shenyang, Wang Fanjie, Xing Qiaoxia, Low Tony, Yan Hugen
Department of Physics, State Key Laboratory of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai 200433, China.
Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
Sci Adv. 2018 Mar 16;4(3):eaap9977. doi: 10.1126/sciadv.aap9977. eCollection 2018 Mar.
The attraction between electrons and holes in semiconductors forms excitons, which largely determine the optical properties of the hosting material, and hence the device performance, especially for low-dimensional systems. Mono- and few-layer black phosphorus (BP) are emerging two-dimensional (2D) semiconductors. Despite its fundamental importance and technological interest, experimental investigation of exciton physics has been rather limited. We report the first systematic measurement of exciton binding energies in ultrahigh-quality few-layer BP by infrared absorption spectroscopy, with layer (L) thickness ranging from 2 to 6 layers. Our experiments allow us to determine the exciton binding energy, decreasing from 213 meV (2L) to 106 meV (6L). The scaling behavior with layer numbers can be well described by an analytical model, which takes into account the nonlocal screening effect. Extrapolation to free-standing monolayer yields a large binding energy of ~800 meV. Our study provides insights into 2D excitons and their crossover from 2D to 3D, and demonstrates that few-layer BP is a promising high-quality optoelectronic material for potential infrared applications.
半导体中电子与空穴之间的吸引力形成了激子，激子在很大程度上决定了主体材料的光学性质，进而决定了器件性能，对于低维系统而言尤其如此。单层和少层黑磷（BP）是新兴的二维（2D）半导体。尽管其具有根本重要性和技术价值，但对激子物理的实验研究相当有限。我们通过红外吸收光谱法首次对高质量少层BP中的激子结合能进行了系统测量，层（L）厚度范围为2至6层。我们的实验使我们能够确定激子结合能，其从213毫电子伏特（2L）降至106毫电子伏特（6L）。层数的标度行为可以用一个考虑了非局部屏蔽效应的解析模型很好地描述。外推到自由单层时得到约800毫电子伏特的大结合能。我们的研究为二维激子及其从二维到三维的转变提供了见解，并表明少层BP是一种有前途的高质量光电子材料，可用于潜在的红外应用。
