Nanostructured surfaces

Photoconductivity spectra of silicon with two structured surfaces
Onyshchenko V.F., Karachevtseva L.A., Karas’ M.I.
Laboratory of Photonic Semiconductor Structures, V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine. Pros. Nauki, 41, Kyiv-03028, Ukraine. 
E-mail: onyshchenkovf@isp.kiev.ua

The silicon surface is structured by pillars, pores, cones and pyramids [1]. A structured silicon surface absorbs light over a wide range of wavelengths. Such a surface not only reduces the reflection of light, but also scatters it, which increases the optical path of light and its absorption in the bulk of silicon [2]. Part of the scattered rays will be completely reflected from another surface due to the fact that they incident at angles greater than the critical angle of total internal reflection. 
The photoconductivity spectra peculiarities in silicon with structured surfaces are calculated depending on the reflection coefficient from the surface. In the presented model of the photoconductivity spectrum, we took into account the multiple reflection of light from partially reflecting structured surfaces. The distribution function of the intensity of electromagnetic radiation in silicon with two structured surfaces versus distance is calculated numerically. It was calculated at what wavelengths the photoconductivity in silicon with two structured surfaces grows efficiently. The extension of the photoconductivity spectra to the long-wavelength region in silicon with two structured surfaces is shown with an increase in the reflection coefficient from the internal structured surface. The reflection coefficient from the internal structured surface increases due to the total internal reflection, which is realized on the internal structured surface. Photoconductivity in silicon with two structured surfaces receives an additional allowance at wavelengths from 0.95 microns to 1.15 microns. This is due to the fact that electromagnetic radiation with wavelengths from 0.95 μm, which is weakly absorbed by silicon, is better reflected from internal structured surfaces. Reflection from internal structured surfaces increases the optical path of light in silicon and its absorption, which increases photoconductivity.

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