Wavelength-Tunable Waveguide Emissions from Electrically Driven Single ZnO/ZnO:Ga Superlattice Microwires

Abstract

Because of the superlattice structures comprising periodic and alternating crystalline layers, one-dimensional photon crystals can be employed to expand immense versatility and practicality of modulating the electronic and photonic propagation behaviors, as well as optical properties. In this work, individual superlattice microwires (MWs) comprising ZnO and Ga-doped ZnO (ZnO/ZnO:Ga) layers were successfully synthesized. Wavelength-tunable multipeak emissions can be realized from electrically driven single superlattice MW-based emission devices, with the dominant wavelengths tuned from ultraviolet to visible spectral regions. To illustrate the multipeak character, single superlattice MWs were selected to construct fluorescent emitters, and the emission wavelength could be tuned from 518 to 562 nm, which is dominated by Ga incorporation. Especially, by introducing Au quasiparticle film decoration, emission characteristics can further be modulated, such as the red shift of the emission wavelengths, and the multipeaks were strongly modified and split into more and narrower subbands. In particular, electrically pumped exciton–polariton emission was realized from heterojunction diodes composed of single ZnO/ZnO:Ga superlattice MWs and p-GaN layers in the blue-ultraviolet spectral regions. With the aid of localized surface plasmons from Au nanoparticles, which deposited on the superlattice MW, significant improvement of emission characteristics, such as enhancement of output efficiencies, blue shift of the dominant emission wavelengths, and narrowing of the spectral linewidth, can be achieved. The multipeak emission characteristics would be originated from the typical optical cavity modes, but not the Fabry–Perot mode optical cavity formed by the bilateral sides of the wire. The resonant modes are likely attributed to the coupled optical microcavities, which formed along the axial direction of the wire; thus, the emitted photons can be propagated and selected longitudinally. Therefore, the novel ZnO/ZnO:Ga superlattice MWs with a quadrilateral cross section can provide a potential platform to construct multicolor emitters and low-threshold exciton–polariton diodes and lasers.

Hybrid quadrupole plasmon induced spectrally pure ultraviolet emission from a single AgNPs@ZnO:Ga microwire based heterojunction diode

“…Moreover, due to the Joule heating effect, the Ag quasiparticle nanolms could be annealed into physically isolated Ag nanoparticles in the emission regions. 23,24,38,39 Thus, the segment of the MW covered by isolated Ag nanoparticles (AgNPs@ZnO:Ga MW) was selected to fabricate heterostructured light-emitting devices. A schematic diagram is provided to explain the emission characteristics of an electrically biased single AgNPs@ZnO:Ga MW based heterostructured light emission device at room temperature, as depicted in Fig.…”

“…Aerwards, Ag quasiparticle nano-lms were deposited on the MW using the magnetron sputtering technique. 23,25,38 Thus, a single ZnO:Ga MW decorated with Ag quasiparticle nanolms (Ag@ZnO:Ga) was fabricated. When the applied bias exceeded a certain value, bright and visible incandescent-type emission was observed, with the emission regions located towards the center of the wire.…”

“…Therefore, a single ZnO:Ga MW covered with Ag nanoparticle decoration (AgNPs@ZnO:Ga) was successfully prepared. 23,25,38 Fabrication of single MW based heterojunction diode A heterojunction light-emitting diode composed of a single MW was constructed, with p-GaN serving as the hole injection layer. Aer being cleaned thoroughly, MgO was deposited on the GaN substrate using the molecular beam epitaxy technique, to serve as an insulating layer.…”

“…Thereby, a single MW based heterojunction diode was fabricated. 6,23,40,42,43 Analysis instruments Single ZnO:Ga MWs, Ag nanostructures, and MWs covered by Ag nanostructures were characterized using scanning electron microscopy (SEM). The current-voltage (I-V) characteristics of the single MW based metal-MW-metal structure and the single MW based heterojunction diode were investigated using a Keysight semiconductor device analyzer (B1500A).…”

“…[17][18][19][20][21] By incorporating noble metal nanostructures, such as Ag nanoparticles, the localized surface plasmon resonance effect has been considered to be an efficient strategy to enhance the luminous efficiency of light-emitting materials and devices, with ZnO micro/nanostructures serving as active layers. [22][23][24] Due to the small sizes of the plasmonic nanostructures, the optical response of the spherical nanostructures embedded in the dielectric materials exhibits dipole surface plasmon resonance modes, which result in strong attenuation of incident light. Nevertheless, owing to serious metallic losses arising from interband electronic transitions, metal plasmons are trapped in the visible spectral band.…”