We demonstrate designs of dielectric-filled anti-reflection coated (ARC) two-dimensional (2D) metallic photonic
crystals (MPhCs) capable of omnidirectional, polarization insensitive, wavelength selective emission/absorption. Up to
26% improvement in hemispherically averaged emittance/absorptance below the cutoff wavelength is observed for
optimized hafnium oxide filled 2D tantalum (Ta) PhCs over the unfilled 2D Ta PhCs. The optimized designs possess
high hemispherically averaged emittance/absorptance of 0.86 at wavelengths below the cutoff wavelength and low
hemispherically averaged emittance/absorptance of 0.12 at wavelengths above the cutoff wavelength, which is extremely
promising for applications such as thermophotovoltaic energy conversion, solar absorption, and infrared spectroscopy.
KEYWORDS: Tantalum, Etching, Solar energy, Photonic crystals, Reactive ion etching, Chromium, Deep reactive ion etching, Solar cells, Black bodies, Lithography
We report highly selective emitters based on high-aspect ratio 2D photonic crystals (PhCs) fabricated on large area (2 inch diameter) polycrystalline tantalum substrates, suitable for high-temperature operation. As an example we present an optimized design for a selective emitter with a cut-off wavelength of 2μm, matched to the bandgap of an InGaAs PV cell, achieving a predicted spectral selectivity of 56.6% at 1200K. We present a fabrication route for these tantalum PhCs, based on standard microfabrication processes including deep reactive ion etch of tantalum by an SF6 based Bosch process, achieving high-aspect ratio cavities (< 8:1). Interference lithography was used to facilitate large area fabrication, maintaining both fabrication precision and uniformity, with a cavity diameter variation of less than 2% across the substrate. The fabricated tantalum PhCs exhibit strong enhancement of the emittance at wavelengths below cut-off wavelength, approaching that of blackbody, and a steep cut-off between high and low emittance spectral regions. Moreover, detailed simulations and numerical modeling show excellent agreement with experimental results. In addition, we propose a surface protective coating, which acts as a thermal barrier coating and diffusion inhibitor, and its conformal fabrication by atomic layer deposition.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.