Abstract
We systematically investigate the effects of surface roughness on the characteristics of ultraviolet zinc oxide plasmonic nanolasers fabricated on aluminium films with two different degrees of surface roughness. We demonstrate that the effective dielectric functions of aluminium interfaces with distinct roughness can be analysed from reflectivity measurements. By considering the scattering losses, including Rayleigh scattering, electron scattering, and grain boundary scattering, we adopt the modified Drude-Lorentz model to describe the scattering effect caused by surface roughness and obtain the effective dielectric functions of different Al samples. The sample with higher surface roughness induces more electron scattering and light scattering for SPP modes, leading to a higher threshold gain for the plasmonic nanolaser. By considering the pumping efficiency, our theoretical analysis shows that diminishing the detrimental optical losses caused by the roughness of the metallic interface could effectively lower (~33.1%) the pumping threshold of the plasmonic nanolasers, which is consistent with the experimental results.
Highlights
IntroductionSince the guided plasmonic mode profiles strongly overlap with the thin gaps, the increase in intrinsic modal loss caused by surface scattering and ohmic damping from surface plasmon polaritons (SPPs) on the rough metallic surface can be significant
Metallic interfaces, are the most promising modes for lasing[6,7,8,9,10,13]
Surface roughness on the Al film can result in scattering losses in the plasmonic nanolasers after deposition of the dielectric spacer layer
Summary
Since the guided plasmonic mode profiles strongly overlap with the thin gaps, the increase in intrinsic modal loss caused by surface scattering and ohmic damping from SPPs on the rough metallic surface can be significant. The surface roughness, which was experimentally obtained by means of atomic force microscopy (AFM), was adopted for evaluating the effective permittivity. Our results reveal that the increase in surface roughness corresponds to stronger intrinsic damping and a larger value of Im[εAl(ω)]. Using both sets (sample A and sample B) of effective permittivity, we discuss the discrepancy of SPP behaviours on the different metallic interfaces. Our study provides a systematic analysis to evaluate the characteristics of plasmonic nanolasers on metallic interfaces with certain degrees of roughness
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