Thickness Scaling Effects on the Complex Optical Conductivity of Few-Layer WSe2 Investigated by Spectroscopic Ellipsometry

2D WSe2 have attracted widespread attentions as an ideal platform for new type optoelectronic and nanoelectronics applications. Understanding the intrinsic thickness scaling effects in complex optical conductivity of 2D, WSe2 is vital for WSe2-based photonic and optoelectronic devices. Herein, complex optical conductivities of 1-5 layers in the energy range of 0.73-6.42 eV by spectroscopic ellipsometry with the classical slab model have been determined. Up to eight feature peaks (A-H) are observed in the optical conductivity spectra, and the central energies of these peaks are identified by the differential spectrum analysis method. These central energies exhibit interesting layer dependencies due to the thickness scaling effects. Specifically, for the low-energy feature peaks A-E, their central energies decrease with the thickness increasing. But for the high-energy feature peaks G and H, their central energies first show significant blueshifts and then redshifts as the thickness increases. These novel layer-dependent evolvements are attributed in the optical conductivity of few-layer WSe2 to the competition mechanism between the decreasing exciton binding energy and the band gap narrowing.

Automated summary

This research investigates the thickness scaling effects on the optical conductivity of WSe2 by using spectroscopic ellipsometry and the classical slab model. The results reveal that the central energies of low-energy feature peaks decrease with increasing thickness, while the central energies of high-energy feature peaks exhibit a blueshift followed by a redshift with thickness. These findings are crucial for understanding the complex optical properties of WSe2.