Narrow-Line-Width Electroluminescence in Monolayer WSe2 Enabled by a Sub-5 nm Au/Pt Nanogap

Spectrally isolated, electrically driven emission from localized states in two-dimensional semiconductors remains challenging in scalable planar devices. Here, we report narrow-line-width alternating-current electroluminescence (ACEL) from localized states in monolayer WSe2 using a lithographically defined sub-5 nm Au/Pt nanogap on SiO2/Si at 3.5 K. The curved nanogap geometry produces a nonuniform strain landscape and regions of enhanced electric field that may influence the local electronic environment. Under square-wave gate excitation, the device exhibits a spectrally isolated ACEL line at 1.652 eV with an apparent fitted line width of approximately 2 meV, in contrast to broad, multipeak photoluminescence from the same device. Spectral decomposition identifies dominant ZPL-like and weaker red-shifted sideband-like contributions. This nanogap architecture provides a scalable planar platform for narrow-line-width, electrically driven localized emission in two-dimensional materials.