Semiconductor Nanowire Plasmonic Lasers
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Nanophotonics 2019; 8(12): 2091–2110 Review article Chun Li, Zhen Liu, Jie Chen, Yan Gao, Meili Li and Qing Zhang* Semiconductor nanowire plasmonic lasers https://doi.org/10.1515/nanoph-2019-0206 Received July 2, 2019; revised October 7, 2019; accepted October 7, 1 Introduction 2019 Rapid development of semiconductor lasers has sig- Abstract: Semiconductor nanowires (NW) hold great nificantly expanded frontier research on semiconductor promise for micro/nanolasers owing to their naturally photonics from fundamental sciences to industrial tech- formed resonant microcavity, tightly confined electromag- nologies, in which device miniaturization has been a netic field, and outstanding capability of integration with long-standing and continuous pursuit. From the creation planar waveguide for on-chip optoelectronic applications. of edge-emitting lasers [1], vertical-cavity surface-emitting However, constrained by the optical diffraction limit, the lasers [2–4], microdisk lasers [5–7], and photonic crystal dimension of semiconductor lasers cannot be smaller than lasers [8–10] to the discovery of nanowire (NW) lasers half the optical wavelength in free space, typically several [11–13], the volume of semiconductor lasers has gradually hundreds of nanometers. Semiconductor NW plasmonic reduced, which is still constrained by the diffraction limit lasers provide a solution to break this limitation and real- and cannot be lower than half the optical wavelength ize deep sub-wavelength light sources. In this review, we (λ), typically several hundred nanometers. This size is an summarize the advances of semiconductor NW plasmonic order of magnitude larger than the feature size of modern lasers since their first demonstration in 2009. First of all, transistors, which would cause integration mismatch and we briefly look into the fabrication and physical/chemi- serious energy dissipation, and thus limit practical appli- cal properties of semiconductor NWs. Next, we discuss the cations of micro/nanolasers [14]. In the past decade, a new fundamentals of surface plasmons as well as the recent type of small lasers, based on surface plasmons (SPs), the progress in semiconductor NW plasmonic lasers from the so-called plasmonic laser, has received widespread atten- aspects of multicolor realization, threshold reduction, tion for achieving deep sub-wavelength laser sources ultrafast modulation, and electrically driven operations, and advancing the development of nano-optics [15–18]. along with their applications in sensing and integrated In plasmonic lasers, optical waves can couple with SPs optics. Finally, we provide insights into bright perspec- occurring at the metal-dielectric interface and store their tives and remaining challenges. energies in free electron oscillations. As a result, the phys- ical dimension of the plasmonic cavity can be compressed Keywords: semiconductor nanowire; plasmonic laser; to the nanometer scale, ultimately enabling the simulta- nanoplasmonics; sub-wavelength optics; photon- plasmon neous amplification of photons and SPs in analogy with interaction. the photonic lasing from pure dielectric materials [19–21]. Meanwhile, strong photon-plasmon interactions sig- nificantly enhance the local field, which allows the plas- *Corresponding author: Qing Zhang, Department of Materials monic laser to deliver high power density, low theoretical Science and Engineering, College of Engineering, Peking University, consumption, and fast response, which are promising for Beijing 100871, PR China; and The State Key Laboratory of regulating linear and nonlinear optical processes [22–27]. Bioelectronics, Southeast University, Nanjing 210096, PR China, So far, the minimum size of the plasmonic laser is com- e-mail: [email protected]. https://orcid.org/0000-0002- parable to that of the metal-oxide-semiconductor field 6869-0381 Chun Li and Jie Chen: Department of Materials Science and effect transistor (~10 nm), and the coupling efficiency Engineering, College of Engineering, Peking University, Beijing with silicon waveguide reaches up to 90%, both making 100871, PR China; and CAS Key Laboratory of Standardization and the plasmonic laser a great candidate to replace electronic Measurement for Nanotechnology, CAS Center for Excellence in circuits in the semiconductor industry. Nanoscience, National Center for Nanoscience and Technology, So far the plasmonic lasing has been demonstrated Beijing 100190, PR China Zhen Liu, Yan Gao and Meili Li: Department of Materials Science in various architectures, which can be mainly divided and Engineering, College of Engineering, Peking University, Beijing into four: (1) metallic nanoparticle lasers with three- 100871, PR China dimensional confinement, such as metal core-dye shell Open Access. © 2019 Qing Zhang et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 Public License. 2092 C. Li et al.: Semiconductor nanowire plasmonic lasers laser [28–30]; (2) metal-insulator-semiconductor wave- without varying the initial doping type and concentration guide (MISW) lasers with two dimensional confinement, [48]. Bottom-up approaches, including chemical vapor e.g. plasmonic NW laser [31]; (3) metal-clad lasers with deposition (CVD), physical vapor deposition, hydro- and one-dimensional confinement, e.g. metal-insulator-metal solvothermal methods, and solution-phase self-assembly, (MIM) laser [32], and (4) plasmonic lattice lasers [33–36]. assemble atomic and molecular units into larger complex The semiconductor NW plasmonic laser based on MISW structures [49–54]. Prior to top-down methods, bottom-up configuration is widely studied owing to its simple struc- strategies could achieve high-quality products and het- ture, facile fabrication, great mode confinement, and long erostructure engineering with low density of destructive propagation length. Furthermore, semiconductor NWs can defects, so they have been employed to grow single- crystal also function as interconnection waveguides, photodetec- NWs of IV, III–V, and II–VI semiconductors including Si, tors, and phototransistors, which are building blocks for Ge, GaAs, InP, ZnO, GaN, CdS, CdSe, etc. [49, 51, 55–58]. optical circuits [37, 38]. The compressed size, improved For example, CsPbBr3 NWs synthesized on mica substrates emission performance, and great device integration with by the CVD method exhibit highly ordered orientation, on-chip networks enable semiconductor NW plasmonic single-crystal structure, and high emission polarization lasers promising for nanophotonic and nanoelectronic ratio of up to 0.78 [59]. Using metal organic chemical vapor applications. deposition (MOCVD), Qian et al. fabricated high-quality Here we summarize the physical and chemical prop- InGaN/GaN quantum well NWs showing tunable compo- erties of semiconductor NWs from the aspects of fabrica- sition and low-threshold, room-temperature, multicolor tion, material photophysics, optical gain/loss, and lasing lasing [60]. Moreover, planar and radial p-n junctions in properties in Section 2. Next, we introduce the funda- NW structures have been allowed in bottom-up routes, mentals of SP and semiconductor NW plasmonic lasers in despite the fact that a homogeneous dopant distribution Sections 3 and 4. From Section 5–9, the progress of these is still desired in thinner NWs considering the high-level plasmonic NW lasers is discussed in terms of multicolor surface states [61, 62]. As solutions, single-ion implanta- operation, threshold reduction, ultrafast response, elec- tion and epitaxial passivation have improved the doping trically pumped devices, and down-to-earth applications, issue and device stability [63, 64]. respectively. Finally, we highlight future perspectives and Benefited from their extremely high aspect ratio and challenges that remain in this field. one dimensionality, NWs are not only of fundamental interest in size and surface effects but also hold great potential for photonic and optoelectronic devices [65–68]. Due to their large refractive index (n) compared to air, 2 Semiconductor nanowires NWs can naturally form active Fabry-Pérot (F-P) optical resonators and function as micro/nanolasers via using the Semiconductor NWs, including several quasi-one- semiconductor as the gain medium [69–71]. As illustrated dimensional nanostructures such as wire, rod, tube, and in Figure 1A, photoluminescence is generated as a semi- strip, have received widespread attention since the 1990s conductor NW is pumped by photons above the bandgap, [39]. The fabrication of semiconductor NWs is mainly propagates along the long axis, and is reflected by the two accomplished by breaking the symmetry and guiding ani- end-facets, and the NW is transformed as an F-P laser if sotropic growth via top-down and bottom-up approaches the pump energy is above the threshold. The gain in the [40]. Top-down approaches reduce the dimension of bulk NW lasers, g, can be described as g = Γgm, where Γ and materials for micrometer and nanometer structures by gm are the confinement factor and material gain, respec- chemical or mechanical thinning routes through mechan- tively. Γ describes the overlap of the optical mode and ical deformation, template-based chemical etching, gain medium, and the photons can be tightly confined in focused ion beam direct writing, and so on [41–43]. Since the NWs, leading to a higher theoretical Γ compared with the size and morphology of NWs can be well controlled other bulk lasers. gm is an inherent property of optical gain in these