Doping controlled Fano resonance in bilayer 1T′-ReS2: Raman experiments and first-principles theoretical analysis

Abstract

In the bilayer ReS₂ channel of a field-effect transistor (FET), we demonstrate using Raman spectroscopy that electron doping (n) results in softening of frequency and broadening of linewidth for the in-plane vibrational modes, leaving the out-of-plane vibrational modes unaffected. The largest change is observed for the in-plane Raman mode at ∼151 cm⁻¹, which also shows doping induced Fano resonance with the Fano parameter 1/q = −0.17 at a doping concentration of ∼3.7 × 10¹³ cm⁻². A quantitative understanding of our results is provided by first-principles density functional theory (DFT), showing that the electron–phonon coupling (EPC) of in-plane modes is stronger than that of out-of-plane modes, and its variation with doping is independent of the layer stacking. The origin of large EPC is traced to 1T to 1T′ structural phase transition of ReS₂ involving in-plane displacement of atoms whose instability is driven by the nested Fermi surface of the 1T structure. Results are compared with those of the isostructural trilayer ReSe₂.