Indirect and direct electronic transitions and electron transport properties of van der Waals NbOCl.

In this paper, the optical and electron transport properties of the two-dimensional (2D) van der Waals (vdW) niobium oxide dichloride (NbOCl) crystal with extremely high second-order nonlinear coefficients are investigated theoretically. We found that the strong absorption of NbOCl in the infrared region is caused by the indirect transition accompanied by phonons and confirmed that the interaction between layers is very weak. However, the study of electron transport properties shows that the interlayer interaction of NbOCl has a certain degree of influence on the scalability of electrical and optical properties. Because of the strong anisotropy of the NbOCl material, it will be a more optimized choice for constructing on-chip photoelectric or thermal devices in the Nb-Cl-Nb direction.