Symmetry induced phonon renormalization in few layers of 2H-MoTe2 transistors: Raman and first-principles studies

Understanding of electron–phonon coupling (EPC) in two-dimensional (2D) materials manifesting as phonon renormalization is essential to their possible applications in nanoelectronics. Here we report in situ Raman measurements of electrochemically top-gated 2, 3 and 7 layered 2H-MoTe2 channel based field-effect transistors. While the  and B2g phonon modes exhibit frequency softening and linewidth broadening with hole doping concentration (p) up to ~2.3 × 10^13/cm^2, A1g shows relatively small frequency hardening and linewidth sharpening. The dependence of frequency renormalization of the  mode on the number of layers in these 2D crystals confirms that hole doping occurs primarily in the top two layers, in agreement with recent predictions.