Abstract
Bragg reflectors with widths down to 300 nm have been fabricated in porous silicon. This was achieved by irradiation of highly-doped p-type silicon with a focused beam of high-energy ions in a channeled alignment, in which the beam is aligned with a major crystallographic direction. The reflected colour is controllably tuned across the visible spectrum by varying the ion irradiated dose. The depth distribution of ion induced defects differs in channeled alignment compared to random beam alignment, resulting in the hole current during subsequent anodisation being more confined to narrower lateral regions, enabling different reflective wavelengths to be patterned on a sub-micron lateral scale. This work provides a means of producing high-density arrays of micron-size reflective colour pixels for uses in high-definition displays, and selectively tuning the wavelengths of porous silicon Fabry-Perot microcavities across the visible and infra-red ranges for optical communications and computing applications.
Highlights
One dimensional photonic structures based on alternating high and low porosity porous silicon layers have found applications in silicon photonics, such as dielectric mirrors in the form of Distributed Bragg Reflectors[1, 2], optical microcavities[3, 4], waveguides[5] and possibly as optical interconnects and switches[6, 7]
Bragg reflectors with widths down to 300 nm have been fabricated in porous silicon
This was achieved by irradiation of highlydoped p-type silicon with a focused beam of high-energy ions in a channeled alignment, in which the beam is aligned with a major crystallographic direction
Summary
One dimensional photonic structures based on alternating high and low porosity porous silicon layers have found applications in silicon photonics, such as dielectric mirrors in the form of Distributed Bragg Reflectors[1, 2], optical microcavities[3, 4], waveguides[5] and possibly as optical interconnects and switches[6, 7]. One dimensional porous silicon Bragg reflectors are produced by periodically raising and lowering the electrochemical hole current flowing through highly-doped p-type silicon during anodisation. The porosity, effective refractive index of each layer, is determined by the hole current density[4, 8]. When each alternating high/low refractive index porous layer has an optical thickness of one quarter of the wavelength of incident light this wavelength is constructively reflected with an efficiency approaching 100% for more than ten pairs of layers. Until recently there has been no means of fabricating highly-reflective arrays of colour filters on a micrometer lateral scale, so applications as high-density reflective displays and in photonics have not been possible
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