Boosting Enhancement of the Electron-Phonon Coupling in Mixed Dimensional CdS/Graphene van der Waals Heterojunction

Electron-phonon coupling plays a key role in affecting the properties of the semiconducting nanostructures, such as providing the possibility for obtaining higher superconducting transition temperatures. Here, using Raman, temperature-dependent and polarized Raman scattering measurements, ultra-strong electron-phonon coupling in 1D CdS nanowires and 2D graphene heterostructures is demonstrated. The intensity ratio of 2LO/1LO mode in CdS nanowires provides a spectroscopy-based method to quantify electron-phonon coupling, the strength of which is temperature and polarization dependent. The intensity ratio mode of 2LO/1LO in heterostructure reached up to 8.95 when the incident laser polarization is parallel to the c-axis of the nanowire. It is approximate to 2.37 times higher than in an individual nanowire. In addition, in situ and time-resolved photoluminescence spectra demonstrate the dynamics of the exciton recombinations, providing a comprehensive understanding of the enhancement of electron-phonon coupling in heterostructures. Via optical waveguiding characterization, the graphene layer is demonstrated to not only be an ultrafast carrier transfer channel but also a low Fermi level channel that induces the formation of the built in electrical field, elevating the electron-phonon coupling. Such new mixed dimensional heterostructures illustrate a straightforward approach to enhance the electron-phonon coupling, which may be applied to many integrated superconducting photonic and optoelectronic devices.