ZnO Nanowires on Single-Crystalline Aluminum Film Coupled with an Insulating WO₃ Interlayer Manifesting Low Threshold SPP Laser Operation

ZnO nanowire-based surface plasmon polariton (SPP) nanolasers with metal-insulator-semiconductor hierarchical nanostructures have emerged as potential candidates for integrated photonic applications. In the present study, we demonstrated an SPP nanolaser consisting of ZnO nanowires coupled with a single-crystalline aluminum (Al) film and a WO₃ dielectric interlayer. High-quality ZnO nanowires were prepared using a vapor phase transport and condensation deposition process via catalyzed growth. Subsequently, prepared ZnO nanowires were transferred onto a single-crystalline Al film grown by molecular beam epitaxy (MBE). Meanwhile, a WO₃ dielectric interlayer was deposited between the ZnO nanowires and Al film, via e-beam technique, to prevent the optical loss from dominating the metallic region. The metal-oxide-semiconductor (MOS) structured SPP laser, with an optimal WO₃ insulating layer thickness of 3.6 nm, demonstrated an ultra-low threshold laser operation (lasing threshold of 0.79 MW cm^-2). This threshold value was nearly eight times lower than that previously reported in similar ZnO/Al₂O₃/Al plasmonic lasers, which were ≈2.4 and ≈3 times suppressed compared to the SPP laser, with WO₃ insulating layer thicknesses of 5 nm and 8 nm, respectively. Such suppression of the lasing threshold is attributed to the WO₃ insulating layer, which mediated the strong confinement of the optical field in the subwavelength regime.