Exciton is a bound state that consisted of one electron and one hole attracted each other by electrostatic Columbic force in materials. Especially in a two-dimensional (2D) semiconductor, an exciton is generated by absorption of a photon with energy larger than band gap and it may survive stably with higher binding energy due to the reduced 2D dimension for weakening dielectric screening effect. Here we report Rydberg-series band-edge excitons of multilayered CuInP₂S₆ observed by micro-thermal-modulated reflectance (μTR) measurements from 10 to 300 K. Bulk CuInP₂S₆ is one of the renowned ferroelectric 2D materials with wider piezoelectric hysteresis loop for electrical memory use. The μTR result demonstrated that multi-layered CuInP₂S₆ of ferroelectric (FE) phase displays prominent band-edge excitonic series that consists of E₁ = 2.958 eV (n = 1), E₂ = 2.993 eV (n = 2) and E_∞ = 3.004 eV (direct gap) at 10 K. The transition amplitude of the E₁ feature is approximately 3 to 4 times larger than that of the E₂ transition for verification of the intrinsic behavior of Rydberg series starting from n = 1. At 300 K, E₂ is ionized and the observed transitions by μTR are E₁ = 2.748 eV and E_∞ = 2.794 eV, respectively. The spontaneous band-edge excitons observed in CuInP₂S₆ render it available for application in optoelectronics devices.

激子是一种束缚态，由一个电子和一个空穴在材料中通过静电库伦力相互吸引。特别是在二维 (2D) 半导体中，激子是通过吸收能量大于带隙的光子产生的，并且由于降低了二维尺寸以削弱介电屏蔽效应，它可以稳定地以更高的结合能生存。在这里，我们报告了通过从 10 到 300 K 的微热调制反射 (μTR) 测量观察到的多层 CuInP ₂ S _{6 的}里德堡系列带边激子。块状 CuInP ₂ S ₆是著名的铁电二维材料之一，具有更宽的压电用于电记忆的磁滞回线。μTR 结果表明多层 CuInP铁电 (FE) 相的₂ S ₆显示出突出的带边激子系列，包括 E ₁  = 2.958 eV (n = 1)、E ₂  = 2.993 eV (n = 2) 和 E _∞  = 3.004 eV（直接间隙）在 10 K。E ₁特征的跃迁幅度比 E ₂跃迁的跃迁幅度大约大 3 到 4 倍，用于验证从 n = 1 开始的里德堡级数的本征行为。在 300 K 时，E ₂被电离并且μTR 观察到的跃迁分别为 E ₁  = 2.748 eV 和 E _∞  = 2.794 eV 。在 CuInP ₂ S _{6 中}观察到的自发带边激子 使其可用于光电器件中。