  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-MoTe$ _{2} $ channel based
field-effect transistors (FETs). While the E$ ^{1}_{2g} $ and B$ _{2g} $ phonon
modes exhibit frequency softening and linewidth broadening with hole doping
concentration (\textit{p}) up to $\sim$ 2.3 $\times$10$ ^{13} $/cm$ ^{2} $, A$
_{1g}$ shows relatively small frequency hardening and linewidth sharpening. The
dependence of frequency renormalization of the E$ ^{1}_{2g} $ 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. We
present first-principles density functional theory (DFT) analysis of bilayer
MoTe$ _{2} $ that qualitatively captures our observations, and explain that a
relatively stronger coupling of holes with E$ ^{1}_{2g} $ or B$ _{2g} $ modes
as compared with the A$ _{1g} $ mode originates from the in-plane orbital
character and symmetry of the states at valence band maximum (VBM). The
contrast between the manifestation of EPC in monolayer MoS$ _{2} $ and those
observed here in a few-layered MoTe$ _{2} $ demonstrates the role of the
symmetry of phonons and electronic states in determining the EPC in these
isostructural systems.
