Electron-phonon scatterings and their roles in vertical charge transport through van der Waals heterostructures

Electron–phonon scattering in solid-state systems is a pivotal process in determining many of key physical quantities such as charged carrier mobilities and lattice thermal conductivities. Here, we report electron tunneling measurements with a semiconducting transition metal dichalcogenide, WSe₂, as the tunnel medium. In van der Waals (vdW)-coupled vertical heterostructures, inelastic quantum tunnel events activated by turbostratic electron–phonon scatterings constructively establish an adjunct transport channel, which drastically increases its loads in vertical charge flows with increasing tunnel medium thickness. Phonons interacting with the tunnel electrons are layer-number dependent, varying by monolayer vs. bi- and triple-layer WSe₂, with an out-of-plane flexural ZA mode as the common excitation. In addition, we find out that second-order electron–phonon scatterings become conspicuous in the multilayered films, involving assorted phonons in the tunnel media and the vdW heterojunctions.