Defect Emission and Its Dipole Orientation in Layered Ternary Znln₂S₄ Semiconductor

Defect engineering is promising to tailor the physical properties of 2D semiconductors for function-oriented electronics and optoelectronics. Compared with the extensively studied 2D binary materials, the origin of defects and their influence on physical properties of 2D ternary semiconductors are not clarified. Here, the effect of defects on the electronic structure and optical properties of few-layer hexagonal Znln₂S₄ is thoroughly studied via versatile spectroscopic tools in combination with theoretical calculations. It is demonstrated that the Zn–In antistructural defects induce the formation of a series of donor and acceptor energy levels and sulfur vacancies induce donor energy levels, leading to rich recombination paths for defect emission and extrinsic absorption. Impressively, the emission of donor–acceptor pair in Znln₂S₄ can be significantly tailored by electrostatic gating due to efficient tunability of Fermi level (E_f). Furthermore, the layer-dependent dipole orientation of defect emission in Znln₂S₄ is directly revealed by back focal plane imagining, where it presents obviously in-plane dipole orientation within a dozen-layer thickness of Znln₂S₄. These unique features of defects in Znln₂S₄ including extrinsic absorption, rich recombination paths, gate tunability, and in-plane dipole orientation are definitely a benefit to the advanced orientation-functional optoelectronic applications.