Influence of Silver Film Quality on the Threshold of Plasmonic Nanowire Lasers

Abstract

Such lasers enable the investigation of enhanced light-matter interactions and can have large impact on applications in the fields of nonlinear optics, sensing, and optical communications. [7][8][9][10][11][12] However, metal-based lasers suffer from high losses, caused by the inherent electron scattering in metals, which leads to an increased lasing threshold and limits their use in applications. To minimize losses and thus improve their performance, it has been suggested to use metal films of high quality which ideally have an ultraflat surface with a high crystalline perfection. [1,[13][14][15][16] Typically, metal films are deposited by thermal evaporation or sputtering. However, the quality of thin metal films is strongly dependent on the growth conditions [17,18] and without careful optimization they are polycrystalline with a surface roughness on the order of a few nanometers. [19,20] Alternatively, the template-stripping method can be used to obtain ultraflat metal films, [21,22] however stripped films are usually still polycrystalline. Optimally, the metal films should be a single crystal with an atomically flat surface over a large area. Epitaxial growth and chemical synthesis have been demonstrated as an effective way to obtain monocrystalline metal films for reducing the metal losses. [13,17,[23][24][25][26] It is known that a high deposition rate and high substrate temperature are essential to obtain epitaxial growth of continuous and flat monocrystalline metal films based on a general deposition system (thermal evaporator or sputtering system). [17,19] In this work, first the film fabrication process for both template-stripping and epitaxial growth based on a thermal evaporator was optimized. Subsequently, the performance of room temperature hybrid plasmonic ZnO nanowire lasers with different silver films (general polycrystalline silver films, template-stripped silver films, and monocrystalline silver films) was characterized.The lasers under study consist of single-crystal, wurtzite ZnO nanowires lying on a silver film with a 10 nm thick magnesium fluoride (MgF 2 ) spacer layer, as shown in Figure 1. [27] The widebandgap semiconductor ZnO (E g ≈ 3.37 eV) emits in the ultraviolet regime (≈380 nm), which is close to the surface plasmon frequency of a silver/air interface. [6,[28][29][30][31] For optimizing the epitaxial growth of silver films, C-axis mica is chosen as a substrate due to its extremely clean and atomically flat surface, low cost, and well lattice-matched crystalline structure with In recent years, the field of plasmonics has become dependent on the ability to maximize the quality of metal films. In particular, plasmonic lasers will require a metal loss as low as possible in order to minimize their operational threshold if they are to find applications. In this article, the findings of recent studies, which report reduced thresholds in plasmonic lasers incorporating high quality metal films with both ultraflat surfaces and high crystallinity, are reassessed. In particular, the role of d...

Unusual scaling laws for plasmonic nanolasers beyond the diffraction limit

“…(3) dominants over the first term. We note that, for both plasmonic and photonic lasers, the absorption from the gain material should contribute a significant portion to the laser threshold 27 . And clearly, the shortened τ induced by small cavity dominants the scaling law in this range.…”

Realization of Perovskite‐Nanowire‐Based Plasmonic Lasers Capable of Mode Modulation

“…By replacing the gain nanowire to nanosquare, the radiation loss can be suppressed effectively by adopting total internal reflection of SPP and the plasmonic laser was demonstrated at room temperature . Additionally, an ultrahigh‐quality crystalline metal film and a closed‐contact planar metal /dielectric layer/semiconductor interface are also beneficial to reduce the ohmic and scattering losses. More importantly, by changing the compound, size and shape of the gain nanomaterials, the plasmonic lasing modes can be effectively manipulated.…”

“…All these plasmonic lasers mentioned above are focused on the conventional semiconductors, including CdS, ZnO, InGaN and GaN, which are usually fabricated with high cost procedures such as high temperature or high vacuum environment. The relevant lasers usually require working at cryogenic temperatures due to the intrinsic ohmic losses in the plasmonic lasers, thus exploring new gain materials to this community is indeed needed.…”

Applications of Hybrid Metal‐Dielectric Nanostructures: State of the Art

“…Root-mean-square (RMS) roughness values ranging from a few nm down to the sub-nanometer scale are usually desirable for achieving a significant low lasing threshold. [351,352] This has called for the use of epitaxial growth techniques like atomic layer deposition (ALD) [353] and molecular beam epitaxy (MBE) [354,355] for growing highly crystalline and ultra-smooth plasmonic substrates, to minimize the scattering losses occurring at the surface corrugations. [356] A different approach for improving the performances in plasmonic hybrid nanolasers has followed after the idea of a semiconductor nanowire-graphene-insulator-metal (GIM) structure, [357] as shown in Figure 28a.…”