Electrical-pumping spasing action from cross-stacked microwires†
The realization of electrically pumped lasers at deep sub-micro and nanometer scale operating far beyond the diffraction limit is still a crucial goal in nanophotonics and plasmonics for prospective fundamental research and application. Herein, electrically pumped spasing action was captured from a cross-stacked architecture composed of a single Ga-doped ZnO microwire (ZnO:Ga MW) crossed with another ZnO:Ga MW covered by Au nanoparticles. To exploit the spasing feature, a plasmonic nanocavity could be constructed based on the sandwiched structures, with isolated Au nanoparticles filling the spacer between the crossed MWs. When both emission regions from the crossed MWs overlapped with each other, the cross-stacked architecture exhibited quasi-Schottky junction behavior, resulting in the formation of a tunneling junction. When the injection current exceeded certain values, bright and localizing emissions were observed at the crossed regions, with a sharp peak emerging in the emission spectra. The dominant emission wavelengths centered at 550 nm were accompanied by the spectral linewidth rapidly narrowing to 2 nm, suggesting a transition from spontaneous to stimulated emission. The electrically pumped lasing characteristics can be attributed to efficient metal plasmons amplification by the stimulated emission of radiation from Au nanoparticles, which filled the nanocavities. Therefore, this cross-stacked architecture provides a natural route towards electrical injection schemes that can be employed to construct electrical-pumping spasers. This technology also provides a candidate to investigate the fabrication of tunneling diodes.