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Exciton-Plasmon Polariton Coupling and Hot Carrier Generation in Two-Dimensional Sib Semiconductors: a First-Principles Study

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Exciton-Plasmon Polariton Coupling and Hot Carrier Generation in Two-Dimensional Sib Semiconductors: a First-Principles Study Nanophotonics 2020; 9(2): 337–349 Research article Ali Ramazani, Farzaneh Shayeganfar, Jaafar Jalilian and Nicholas X. Fang* Exciton-plasmon polariton coupling and hot carrier generation in two-dimensional SiB semiconductors: a first-principles study https://doi.org/10.1515/nanoph-2019-0363 Received September 15, 2019; revised November 27, 2019; accepted List of nonstandard abbreviations December 9, 2019 DFT Density functional theory Abstract: Exciton (strong electron–hole interactions) and HCs Hot carriers QPs Quasiparticles hot carriers (HCs) assisted by surface plasmon polaritons SP Surface plasmon show promise to enhance the photoresponse of nanoelec- SPP Surface plasmon polariton tronic and optoelectronic devices. In the current research, H-SiB Semihydrogenated SiB we develop a computational quantum framework to study BSE Beth–Salpeter Equation the effect of coupled exciton and HCs on the photovoltaic MFP Mean free path energy distribution, scattering process, polarizability, and light emission of two-dimensional (2D) semiconductors. Using a stable 2D semiconductor (semihydrogenated SiB) 1 Introduction as our example, we theoretically show that external strain and thermal effect on the SiB can lead to valley polarized After the first isolation of two-dimensional (2D) gra- plasmon quasiparticles and HC generation. Our results phene monolayers in 2004 [1, 2], additional novel 2D reveal that the electron–phonon and electron–electron nanomaterials with similar properties have been sought (e–e) interactions characterize the correlation between for a wide range of applications. Recently, new gra- the decay rate, scattering of excitons, and generation of phene-like materials made by combining groups III–IV HCs in 2D semiconductors. Moreover, phonon assisted elements have become of great interest. For instance, luminescence spectra of SiB suggest that light emission Tománek et al. [3] have investigated structural and elec- can be enhanced by increasing strain and temperature. tronic properties of 2D boron–carbide monolayers, such The polarized plasmon with strong coupling of electronic as BC, BC3, BC5, and BC7 by utilizing first-principles calcu- and photonics states in SiB makes it as a promising candi- lations. Their results demonstrated that those structures date for light harvesting, plasmonic photocurrent devices, possess suitable structural stability and semiconduct- and quantum information. ing characteristics. Due to the outstanding properties of these compounds, many computational and experi- Keywords: surface plasmon; hot carrier; valley polaritons; mental research groups have sought to understand luminescence; strain engineering. their structure–property relationship for a wide range of applications such as superconductivity [4], electrical devices [5], half-metallicity [6], and hydrogen storage [7]. For instance, the structure and properties of 2D boron– silicon have been predicted computationally using first- *Corresponding author: Nicholas X. Fang, Department of Mechanical Engineering, Massachusetts Institute of Technology, principles calculations. For example, Hansson et al. Cambridge, MA, USA, e-mail: [email protected]. https://orcid. [8] determined that low-dimensional honeycomb SiB org/0000-0001-5713-629X nanosheets possess metallic behavior. They found that Ali Ramazani: Department of Mechanical Engineering, this compound is of satisfactory structural stability rela- Massachusetts Institute of Technology, Cambridge, MA, USA tive to silicene and boron sheets [9–11]. Unlike Hansson Farzaneh Shayeganfar: Department of Civil and Environmental Engineering, Rice University, Houston, TX, USA et al. [8], who stated that the boron and silicon atoms Jaafar Jalilian: Department of Physics, College of Sciences, Yasouj are distributed alternately in the honeycomb SiB lattice, University, Yasouj, Iran Dai et al. [12] presented a new stable 2D SiB structure Open Access. © 2020 Nicholas X. Fang et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 Public License. 338 A. Ramazani et al.: Exciton-plasmon polariton coupling and hot carrier generation in 2D SiB semiconductors consisting of uniformly distributed boron dimers and In the current research, we first studied the stability silicon dimers. This new configuration expresses a non- and electronic properties of honeycomb SiB monolay- magnetic metallic behavior for SiB [12]. Ding and Wang ers using first-principles calculations. Different surface [13] showed using first-principles calculations that a functionalization configurations are considered to attain 2D SiB monolayer possesses a washboard-like buckled structural stability and to tailor the electronic properties structure, but they did not address its structural stabil- of a functionalized SiB monolayer. Optical properties of ity. Recently, Aizawa et al. [14] reported the fabrication SiB and semihydrogenated SiB (H-SiB) (the most stable of 2D silicon–boron compounds on the ZrB2(0001) as functionalized structure) are then estimated. We com- a good substrate for B or Si adsorption. Their findings putationally illustrated how to tune the bandgap and suggest that Si3B6 can reproduce the measured phonon accordingly on the light absorption on the surface of the dispersion by using high-resolution electron energy-loss materials with strain engineering. Second, we employed spectroscopy. a comprehensive quantum approach of light emission Surface plasmon polaritons (SPPs) are the most from SPP semiconductor to link the HC generation to light common type of hybrid modes of photons and excited emission and open an avenue to the experimentalists charge dipole in crystals [15, 16]. Surface plasmon polar- how to use PL spectroscopy to harvest long-lived HC light itons can be engineered to have photocurrent energy in emission and optimize the efficiency of SPP detectors. the desired wavelength and long lifetime [16, 17]. Surface Our study describes how to apply external stimuli such plasmon polariton excitation by photon absorption as strain and temperature to enhance the luminescence creates hot carriers (HCs) as any energetic electron or hole from SP in low dimensional semiconductors consider- through plasmon polariton decay. Photocurrent energy ing both e–ph and e–e scattering and polarizability, as and resonance energy with controlled HCs flow [18] are two main factors, to enhance the light emission. Impor- determined by tuning two factors of size and shape in tantly, our quantum computational approach quanti- plasmonic nanomaterials [19]. Ultrafast relaxation of HCs tatively describes HC distribution as a feature in the HC makes capturing of them a difficult premise [20]. To over- generation process in both unstrained and strained 2D come their limitation of short lifetime [20] and maximize semiconductors. the photocurrent efficiency [21, 22], the decay rate and scattering path of hot holes and electrons must be speci- fied [23]. Several experiments can probe this dynamic path directly in metals through time-resolved ultrafast 2 Methods pump probe [24] or indirectly by scanning changes of SP Density functional theory (DFT) is used to study the effect resonances [25]. For following of electro-optic and vibra- of surface functionalization on the stability and electronic tional modes in molecules, fluorescence is a powerful and optical properties of a honeycomb SiB monolayer and tool [26], while light emission in metals is weaker than the effect of strain on its electronic and optical proper- molecules due to strong electron–electron (e–e) interac- ties. Density functional perturbation theory [32], as imple- tion and electron–phonon (e–ph) coupling [27]. Barati mented in QUANTUM ESPRESSO [33], Green’s function and et al. [28] reported efficient electron–hole (e–h) pair gen- time-dependent DFT were employed to compute the excited eration in the transition-metal dichalcogenides (TMDs) states and effect of temperature on the photo illumination semiconductors at temperatures near T = 300 K, resulting of H-SiB. in 350% enhancement in the optoelectronic responsively [28]. Zhang et al. [29] investigated the polariton disper- sions and anticrossing mode in TMDs and reported the existence of polariton modes at room temperature ana- 2.1 Electronic and optical properties lyzing the PL and reflectance spectrum experimentally. calculations Experimental study by Chen et al. [30] revealed that the light–matter quasiparticles (QPs), as valley-polarized The electronic properties of SiB and H-SiB and the optical plasmon polaritons, emit polarized light in the embedded properties of H-SiB were computed utilizing first-princi- 2D MoS2 semiconductor in a cavity. The dispersive phonon ples many-body perturbation theory (MBPT) BerkeleyGW polariton modes have also been reported in the hexagonal (BGW) (BerkeleyGW, Oakland, CA, USA) [34–36] package boron nitride monolayer and its heterostructure with gra- with a Perdew, Burke, and Ernzerhof starting point. GW phene, where mid-infrared (IR) optical properties can be approach and Beth–Salpeter equation (BSE) are described observed due to phonon polariton modes [31]. in Sections S3 and S4 in SI, respectively. A. Ramazani et al.: Exciton-plasmon polariton coupling and hot carrier generation in 2D SiB semiconductors 339 2.2 Exciton–plasmon interaction in semiconductors The main parameters in the calculation of exciton– plasmon interaction are noninteracting χ0(q, ω) and interacting χ(q, ω) polarizability. The density–density response function of noninteracting electrons
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