Chalcogenide glasses for advanced photonic and photovoltaic applications
Date
2015
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
Chalcogenide glasses, namely the amorphous compounds containing sulfur,
selenium, and/or tellurium, have emerged as a promising material candidate for
integrated photonics given their wide infrared transparency window, low processing
temperature, almost infinite capacity for composition alloying, as well as high linear
and nonlinear indices. Here we present the fabrication and characterization of
chalcogenide glass based photonic devices integrated on silicon, solar cells as well as
on flexible polymer substrates for advanced photonic and photovoltaic applications.
In this work we developed a low-cost method to deposit glassy films while
retaining glass stoichiometry and high optical quality for photonic and photovoltaic
applications. As2Se3 amorphous thin films were prepared by standard spin-coating
techniques from their organic amine solution with glass loading concentrations as high
as 0.5 g/ml. The prepared films were stabilized at elevated temperatures. Physiochemical
properties of the spin-coated films were studied and compared with thermal
evaporated As2Se3 thin film.
ChG photonic devices including gratings, waveguides and resonators, can be
fabricated using nanoimprint. This technique offers a convenient, high-throughput,
and low-cost approach for patterning of sub-micron glass structures. We rationalized
the processing design and modified the material composition to successfully pattern
the glass structures. Finite element analysis aligned well with the experimental
imprinting results. The imprinted resonators exhibited an ultra-high quality factor of 4
× 10^5 near 1550 nm wavelengths, which represents the highest value reported in
chalcogenide glass microring resonators.
We further demonstrated that nanoimprint is a versatile technique for the
fabrication of photonic structures on flexible polymer substrates. Waveguides,
microring resonators, and diffraction gratings fabricated from solution processed ChG
films can be monolithically integrated with organic polymer substrates to create
mechanically flexible, high-index-contrast photonic devices. The resonators exhibit a
high quality factor (Q-factor) of 80 000 near 1550 nm wavelength. Free-standing,
flexible ChG gratings whose diffraction properties can be readily tailored by
conformal integration on nonplanar surfaces are also demonstrated.
Lastly, chalcogenide glasses can be used for the solar cell light trapping
applications. We theoretically analyzed and numerically designed novel light-trapping
grating structures which provides light trapping enhancement well exceeding the
conventional Lambertian limit, by breaking the structural symmetry in conventional
grating designs to maximize the guided mode contribution to optical absorption. The
light-trapping enhancement in Si solar cells was numerically studied by optimizing the
grating parameters. The results showed that the optimized 1-D gratings lead to 63%
increase in optical path length, which represents 44% relative improvement compared
to the path length enhancement factor using conventional light-trapping structures. I
integrated the gratings with thin c-Si solar cells and characterized the solar cells
performance. The enhanced solar cell efficiency from 12.2% to 13% after the
integration of gratings and backside reflector proves the effect of the light-trapping.