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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 4 — Feb. 14, 2011
  • pp: 3316–3331

Ray optical light trapping in silicon microwires: exceeding the 2n2 intensity limit

Emily D. Kosten, Emily L. Warren, and Harry A. Atwater  »View Author Affiliations

Optics Express, Vol. 19, Issue 4, pp. 3316-3331 (2011)

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We develop a ray optics model of a silicon wire array geometry in an attempt to understand the very strong absorption previously observed experimentally in these arrays. Our model successfully reproduces the n2 ergodic limit for wire arrays in free space. Applying this model to a wire array on a Lambertian back reflector, we find an asymptotic increase in light trapping for low filling fractions. In this case, the Lambertian back reflector is acting as a wide acceptance angle concentrator, allowing the array to exceed the ergodic limit in the ray optics regime. While this leads to increased power per volume of silicon, it gives reduced power per unit area of wire array, owing to reduced silicon volume at low filling fractions. Upon comparison with silicon microwire experimental data, our ray optics model gives reasonable agreement with large wire arrays (4 μm radius), but poor agreement with small wire arrays (1 μm radius). This suggests that the very strong absorption observed in small wire arrays, which is not observed in large wire arrays, may be significantly due to wave optical effects.

© 2011 Optical Society of America

OCIS Codes
(000.6590) General : Statistical mechanics
(030.5630) Coherence and statistical optics : Radiometry
(080.0080) Geometric optics : Geometric optics
(260.6970) Physical optics : Total internal reflection
(350.6050) Other areas of optics : Solar energy

ToC Category:
Solar Energy

Original Manuscript: November 22, 2010
Manuscript Accepted: January 25, 2011
Published: February 4, 2011

Emily D. Kosten, Emily L. Warren, and Harry A. Atwater, "Ray optical light trapping in silicon microwires: exceeding the 2n2 intensity limit," Opt. Express 19, 3316-3331 (2011)

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