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Understanding of electron-phonon coupling (EPC) in two dimensional (2D)materials manifesting as phonon renormalization is essential to their possibleapplications in nanoelectronics. Here we report in-situ Raman measurements ofelectrochemically top-gated 2, 3 and 7 layered 2H-MoTe$ _{2} $ channel basedfield-effect transistors (FETs). While the E$ ^{1}_{2g} $ and B$ _{2g} $ phononmodes exhibit frequency softening and linewidth broadening with hole dopingconcentration (\textit{p}) up to $\sim$ 2.3 $\times$10$ ^{13} $/cm$ ^{2} $, A$_{1g}$ shows relatively small frequency hardening and linewidth sharpening. Thedependence of frequency renormalization of the E$ ^{1}_{2g} $ mode on thenumber of layers in these 2D crystals confirms that hole doping occursprimarily in the top two layers, in agreement with recent predictions. Wepresent first-principles density functional theory (DFT) analysis of bilayerMoTe$ _{2} $ that qualitatively captures our observations, and explain that arelatively stronger coupling of holes with E$ ^{1}_{2g} $ or B$ _{2g} $ modesas compared with the A$ _{1g} $ mode originates from the in-plane orbitalcharacter and symmetry of the states at valence band maximum (VBM). Thecontrast between the manifestation of EPC in monolayer MoS$ _{2} $ and thoseobserved here in a few-layered MoTe$ _{2} $ demonstrates the role of thesymmetry of phonons and electronic states in determining the EPC in theseisostructural systems.

Symmetry induced phonon renormalization in few layers of 2H-MoTe$_2$ transistors: Raman and first-principles studies