Enhanced Ultraviolet Spontaneous and Lasing Emission Through Interface Engineering of Patterned Vertically Aligned ZnO Nanowires

Abstract

Among the most studied nanomaterials, 1D nanowires (NWs) with ultra-high intrinsic photoelectric gain, multiple array light confinement, and subwavelength size effects could be suitable for designing structures with advanced performance, which fully satisfy the practical needs. [9][10][11][12] Due to the small size and self-formed cavity, semiconductor NWs have attracted more and more attention to fabricating nanostructured lasers, [13] which could provide natural cavities for low size lasers. [15][16][17][18] Among all the low dimensional materials, ZnO is considered to be a promising candidate as a UV media considering its wide bandgap (3.37 eV) and large exciton binding energy of 60 meV, which is suitable for fabricating room temperature optoelectronic devices. [19][20][21] Compared with GaN (25 meV), the large exciton binding energy of ZnO material enables to achieve room temperature optoelectronic devices with high stability. At present, optically pumped UV lasing action in ZnO was realized as the gain medium with single forms such as microwires, microspheres, nanoribbons, nanowires, etc. [22][23][24][25] and the preparation methods could be thermal oxidation, chemical vapor deposition (CVD), hydrothermal reaction, magnetron sputtering, atomic layer deposition (ALD), pulsed laser Due to optical radiation losses, a high pumping threshold or low temperature is necessary for driving ultraviolet (UV) light emission devices, and surface/interface engineering method is one of the alternatives for tailoring photon behavior. Here, a fully integrated nanowire (NW) laser device is thus constructed, resulting in suppressed interface light loss. Enhanced UV spontaneous and lasing emission is observed due to adequate gain to compensate for the optical loss. Applying well-aligned ZnO NW cavities, optimized UV spontaneous and lasing emission is realized, supporting an effective optical path through interface engineering for photon extraction. As proven by experimental results, through interface integration with Pt metal for ZnO NWs, 170% photoluminescence (PL) emission enhancement accompanied by 145% broaden emission spectra width in the UV region is obtained. It is also observed that more lasing modes appeare when excitation density is high enough, lasing modes interspacing of around 3 nm, and full width at half maximum of the modes <0.003 eV for the lasing device could be observed. The detailed optical simulation is proposed to understand the physical origin of internal mechanisms contributing to the optimized spontaneous and stimulated lasing emission behaviors.