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Transmission enhancement based on strong interference in metal-semiconductor layered film for energy harvesting.

Li Q, Du K, Mao K, Fang X, Zhao D, Ye H, Qiu M - Sci Rep (2016)

Bottom Line: In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection.These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance.This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China.

ABSTRACT
A fundamental strategy to enhance optical transmission through a continuous metallic film based on strong interference dominated by interface phase shift is developed. In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection. For a 50-nm-thick Ag film, experimental transmission enhancement factors of 4.5 and 9.5 are realized by exploiting Ag/Si non-symmetric and Si/Ag/Si symmetric geometries, respectively. These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance. Considering one of their potential applications as transparent metal electrodes in solar cells, a calculated 182% enhancement in the total transmission efficiency relative to a single metallic film is expected. This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.

No MeSH data available.


Related in: MedlinePlus

(a) A representation (both schematic diagram and SEM image of cross-section) of the double-layered film with enhanced transmission, comprising a high refractive index dielectric layer on an optically thin metallic film on a glass substrate. The scale bar is 100 nm. (b) Real and imaginary parts of the complex refractive indices of Ag and Si. (c) Real and imaginary parts and (d) phase shift (in degree) of the complex reflection coefficient at Ag/Si interface at normal incidence.
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f1: (a) A representation (both schematic diagram and SEM image of cross-section) of the double-layered film with enhanced transmission, comprising a high refractive index dielectric layer on an optically thin metallic film on a glass substrate. The scale bar is 100 nm. (b) Real and imaginary parts of the complex refractive indices of Ag and Si. (c) Real and imaginary parts and (d) phase shift (in degree) of the complex reflection coefficient at Ag/Si interface at normal incidence.

Mentions: To demonstrate the concept of enhanced optical transmission based on strong interference effect in a thin planar metal/semiconductor double-layered film, a semiconductor layer (such as Si, Ge and GaAs) is deposited on a metallic (such as Au, Ag, Al and Cu) layer to create strong interference in between, as illustrated in Fig. 1. The whole structure is placed on a transparent glass substrate (n = 1.45). Here amorphous silicon (a-Si) and Ag are used as semiconductor and metal materials, respectively. Figure 1a also presents the SEM image of the Ag/Si double layered film. The boundary between the substrate layer and Ag layer is clear. Figure 1b presents measured real and imaginary parts of the complex refractive indices of sputtered Ag and a-Si using a spectroscopic ellipsometer. The a-Si is highly absorbing at visible frequencies owing to direct electronic transitions at energies above the absorption edge. The Ag thickness is controlled to be below 60 nm. The a-Si thickness h ranges from 10 to 25 nm; therefore, h ≪ λ/4n (λ is the light wavelength and n is the real part of the complex refractive index) is satisfied in the visible range. This ultra-thin Si layer markedly alters the reflection as well as the transmission of the Ag film. The transmission peak wavelength can be altered by varying the Si layer thickness. At optical frequencies from 400 to 780 nm, the metal has a finite conductivity and corresponding a finite complex refractive index () while the semiconductor exhibits a high refractive index together with a high loss (). Therefore, a non-trivial phase shift can be formed at the interface. Figure 1c,d present real and imaginary parts and phase shift (in degree) of the complex reflection coefficient at Ag/Si interface at normal incidence. It can be seen that significant imaginary parts exist in the complex reflection coefficient. Subsequently, the Ag/Si interface phase shift is around 90° from 400 to 780 nm, in sheer contrast with conventional interface phase shift (0° or 180°) between two lossless dielectrics. This non-trivial Ag/Si interface phase shift combines the Air/Si and Ag/SiO2 interface phase shifts and propagation phase shifts to create absorption and transmission resonances for certain semiconductor film thicknesses below λ/4n.


Transmission enhancement based on strong interference in metal-semiconductor layered film for energy harvesting.

Li Q, Du K, Mao K, Fang X, Zhao D, Ye H, Qiu M - Sci Rep (2016)

(a) A representation (both schematic diagram and SEM image of cross-section) of the double-layered film with enhanced transmission, comprising a high refractive index dielectric layer on an optically thin metallic film on a glass substrate. The scale bar is 100 nm. (b) Real and imaginary parts of the complex refractive indices of Ag and Si. (c) Real and imaginary parts and (d) phase shift (in degree) of the complex reflection coefficient at Ag/Si interface at normal incidence.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940859&req=5

f1: (a) A representation (both schematic diagram and SEM image of cross-section) of the double-layered film with enhanced transmission, comprising a high refractive index dielectric layer on an optically thin metallic film on a glass substrate. The scale bar is 100 nm. (b) Real and imaginary parts of the complex refractive indices of Ag and Si. (c) Real and imaginary parts and (d) phase shift (in degree) of the complex reflection coefficient at Ag/Si interface at normal incidence.
Mentions: To demonstrate the concept of enhanced optical transmission based on strong interference effect in a thin planar metal/semiconductor double-layered film, a semiconductor layer (such as Si, Ge and GaAs) is deposited on a metallic (such as Au, Ag, Al and Cu) layer to create strong interference in between, as illustrated in Fig. 1. The whole structure is placed on a transparent glass substrate (n = 1.45). Here amorphous silicon (a-Si) and Ag are used as semiconductor and metal materials, respectively. Figure 1a also presents the SEM image of the Ag/Si double layered film. The boundary between the substrate layer and Ag layer is clear. Figure 1b presents measured real and imaginary parts of the complex refractive indices of sputtered Ag and a-Si using a spectroscopic ellipsometer. The a-Si is highly absorbing at visible frequencies owing to direct electronic transitions at energies above the absorption edge. The Ag thickness is controlled to be below 60 nm. The a-Si thickness h ranges from 10 to 25 nm; therefore, h ≪ λ/4n (λ is the light wavelength and n is the real part of the complex refractive index) is satisfied in the visible range. This ultra-thin Si layer markedly alters the reflection as well as the transmission of the Ag film. The transmission peak wavelength can be altered by varying the Si layer thickness. At optical frequencies from 400 to 780 nm, the metal has a finite conductivity and corresponding a finite complex refractive index () while the semiconductor exhibits a high refractive index together with a high loss (). Therefore, a non-trivial phase shift can be formed at the interface. Figure 1c,d present real and imaginary parts and phase shift (in degree) of the complex reflection coefficient at Ag/Si interface at normal incidence. It can be seen that significant imaginary parts exist in the complex reflection coefficient. Subsequently, the Ag/Si interface phase shift is around 90° from 400 to 780 nm, in sheer contrast with conventional interface phase shift (0° or 180°) between two lossless dielectrics. This non-trivial Ag/Si interface phase shift combines the Air/Si and Ag/SiO2 interface phase shifts and propagation phase shifts to create absorption and transmission resonances for certain semiconductor film thicknesses below λ/4n.

Bottom Line: In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection.These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance.This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China.

ABSTRACT
A fundamental strategy to enhance optical transmission through a continuous metallic film based on strong interference dominated by interface phase shift is developed. In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection. For a 50-nm-thick Ag film, experimental transmission enhancement factors of 4.5 and 9.5 are realized by exploiting Ag/Si non-symmetric and Si/Ag/Si symmetric geometries, respectively. These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance. Considering one of their potential applications as transparent metal electrodes in solar cells, a calculated 182% enhancement in the total transmission efficiency relative to a single metallic film is expected. This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.

No MeSH data available.


Related in: MedlinePlus