Biomimetic subwavelength antireflective gratings on GaAs

Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, USA.
Optics Letters (Impact Factor: 3.29). 11/2008; 33(19):2224-6. DOI: 10.1364/OL.33.002224
Source: PubMed


We have developed a simple and scalable bottom-up approach for fabricating moth-eye antireflective coatings on GaAs substrates. Monolayer, non-close-packed silica colloidal crystals are created on crystalline GaAs wafers by a spin-coating-based single-layer reduction technique. These colloidal monolayers can be used as etching masks during a BCl(3) dry-etch process to generate subwavelength-structured antireflective gratings directly on GaAs substrates. The gratings exhibit excellent broadband antireflective properties, and the specular reflection matches with the theoretical prediction using a rigorous coupled-wave analysis model. These bioinspired antireflection coatings have important technological applications ranging from efficient solar cells to IR detectors.

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Available from: Bin Jiang, Dec 10, 2014
    • "Also, the problem with the matching of the thermal expansion coefficient of an antireflective multilayer film can be overcome by ''moth'' eye structure. Therefore, the extensive research efforts have primarily focused on the external reflective structure1234567. However, in contrast to solar cells and other photosensitive devices, the light extraction efficiency enhancement of light-emitting diodes (LEDs) is limited crucially by the behavior of internal reflection. "
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    ABSTRACT: We present that the internal reflective triangular-groove grating can be effectively analyzed and designed by the developed scalar diffraction theory and the effective medium theory at the certain feature size. This grating profile could be applied in enhancing significantly the light extraction efficiency of light-emitting diodes. The accuracy of these both uncomplicated methods is quantitatively evaluated by the comparison of diffraction efficiencies predicted from them to exact results calculated by the rigorous coupled wave analysis method. When the normalized period of a grating is more than fourfold wavelengths of emitted light, the developed scalar diffraction theory is accurate and useful to analyze the internal reflective triangle grating. As the higher order diffraction waves other than zero order wave is not to propagate, the effective medium theory can precisely evaluate the transmittance within the error of about 1.2%. Besides, the used limitation of these simple methods as a function of the normalized height is also quantitatively determined. Furthermore, the transmission characteristics of manufacturing deficiencies of an internal reflection grating as a function of the groove width are quantitatively calculated by using the rigorous coupled wave analysis.
    No preview · Article · Apr 2013 · Optics and Lasers in Engineering
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    • "The anti-reflection coatings made using this bottom-up non-lithographic technique were found to exhibit broadband antireflective performance superior to commercial coatings. Similar biomimetic anti-reflection coatings have also been used for GaAs substrates [30]. The nanonipple array also enhances hydrophobicity [31,32] so that the surface is self-cleaning [33]. "
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    ABSTRACT: All three methodologies of engineered biomimicry – bioinspiration, biomimetics, and bioreplication – are represented in current research on harvesting solar energy. Both processes and porous surfaces inspired by plants and certain marine animals, respectively, are being investigated for solar cells. Whereas dye-sensitized solar cells deploy artificial photosynthesis, bioinspired nanostructuring of materials in solar cells improves performance. Biomimetically textured coatings for solar cells have been shown to reduce optical reflectance and increase optical absorptance over a broad spectral regime. Compound lenses fabricated by a bioreplication technique offer similar promise for reduced reflectance by increasing the angular field of view.
    Full-text · Article · Jan 2012 · International Journal of Smart and Nano Materials
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    • "1/ ( ) [ ( ) (1 ( )) ] q q q GaAs air n z f z n f z n = + − , where q=2/3 [16] "
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    ABSTRACT: We demonstrate nanoscale antireflection structures on GaAs substrate with linearly graded effective refractive index using a lenslike shape transfer for broadband light-absorbing device application. From reflectance calculation of cone- and parabola-shaped subwavelength grating (SWG) structures, it is found that the parabola shaped structures has lower mean reflectance compared to that of the cone shaped structures over a wide wavelength range. The fabricated SWG structures with parabola shape show the reflectance of below 5 % in a 300-1200 nm wavelength range.
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