Crystal Growth and Excitonic Transition of High-Quality Rhombohedral ZnIn₂S₄ Layered Semiconductor

Ching-Hwa Ho¹, Pin-Chia Chen^1*

¹Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan

* Presenter:Pin-Chia Chen, email:a0927668800@gmail.com

Layered ZnIn₂S₄ (ZIS) single crystals were synthesized via chemical vapor transport. The material crystallizes in a rhombohedral phase, and cross-sectional TEM images reveal atomically ordered layers consistent with theoretical predictions, confirming its high crystalline quality. Raman spectroscopy exhibits thickness-dependent vibrational features, evidencing interlayer coupling in few-layer structures. Optical analyses show that ZIS is a direct-bandgap semiconductor with a bandgap energy of 2.76 eV at room temperature, which blue-shifts to 2.90 eV at 20 K due to reduced lattice vibrations. Thermoreflectance (TR) spectra display a pronounced A1 excitonic feature corresponding to the fundamental bandgap, along with a well-resolved B1 exciton and the emergence of higher-energy B2 excitons at low temperature, reflecting the evolution of the excitonic transition. The fabricated ZIS-based devices exhibit low dark current and strong, stable photoresponse under ultraviolet illumination, demonstrating their high sensitivity and fast carrier dynamics. These findings highlight the strong interlayer interactions, optical anisotropy, and excellent optoelectronic quality of ZIS single crystals, suggesting their promising potential for next-generation UV photodetectors and related optoelectronic applications.

Keywords: 2D semiconductors, Crystal Growth, Band Structure, Direct Bandgap, Exciton Transition