Electron-Hole Asymmetry in the Electron-phonon Coupling in Top-gated Phosphorene Transistor

TL;DR

This study reveals that in phosphorene transistors, phonons with A$_g$ symmetry are more affected by electron doping than holes, due to the distinct electronic band structures involving $ ext{pi}$ and $ ext{sigma}$ bonding states.

Contribution

It demonstrates the electron-hole asymmetry in electron-phonon coupling in phosphorene and explains it through first-principles analysis, highlighting Raman spectroscopy as a tool for measuring electron concentration.

Findings

A$_g$ phonons depend strongly on electron concentration

B$_g$ phonons are insensitive to doping

Electron-hole asymmetry explained by band structure differences

Abstract

Using in-situ Raman scattering from phosphorene channel in an electrochemically top-gated field effect transistor, we show that its phonons with A$_g$ symmetry depend much more strongly on concentration of electrons than that of holes, while the phonons with B$_g$ symmetry are insensitive to doping. With first-principles theoretical analysis, we show that the observed electon-hole asymmetry arises from the radically different constitution of its conduction and valence bands involving $\pi$ and $\sigma$ bonding states respectively, whose symmetry permits coupling with only the phonons that preserve the lattice symmetry. Thus, Raman spectroscopy is a non-invasive tool for measuring electron concentration in phosphorene-based nanoelectronic devices.