Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Amorphous Silicon Nanodisk Mie Resonator Arrays
KTH, School of Information and Communication Technology (ICT).
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Arrays of sub-wavelength nanowires and metal particles have been investigated for optical absorption enhancement in photonic devices, e.g., photo-detectors, solar cells and LEDs. Recently, arrays of subwavelength dielectric nanodisk structures were demonstrated as a suitable solution for light absorption enhancement wherein the nanodisks, acting as Mie resonators, enhance forward light scattering into the absorbing material. Depending on the applications, such Mie resonators can also be used for enhanced light absorption. Besides c-Si and a-Si, metal-oxide or III-V nanodisks can be integrated on Si photo-detectors and solar cells.

In this work, the optical properties of substrate-free amorphous silicon (a-Si) nanodisk Mie resonator arrays are investigated. This was done by electromagnetic modelling and simulations, using Lumerical finite difference time domain (FDTD) simulations, and by fabricating substrate-free a-Si nanodisk arrays and embedding them in polydimethylsiloxane (PDMS) for optical characterization. In addition, transfer printing has been investigated using a PDMSstamp for transferring the nanodisk arrays as well as micro-structures onto a different substrate.

The effect of the nanodisk diameter (200-350 nm), height (150-300 nm), array period (450-550 nm) and material (e.g., a-Si, c-Si and InP) on light reflection, transmission and absorption properties of the nanodisk arrays are investigated by FDTD simulations. The reflectivity spectra show clear dips due to the array (hexagonal and square lattices) periodicity and due to Mie resonances of the nanodisks. For the reflectivity dip(s) due to Mie resonance(s) a systematic red-shift with increasing disk diameter is observed. In addition, compared to bare Si substrate the reflectance spectra of nanodisks on Si show significant reduction in reflectivity for above bandgap light due to predominantly forward light scattering into the Si substrate.

Colloidal Lithography (CL), using self-assembled SiO2 colloidal particles as an etch mask, combined with inductively coupled plasma reactive ion etching (ICP-RIE) based on a pseudoBosch process were used to fabricate a-Si nanodisk arrays. The samples consisted of a-Si/SiO2 or SiO2/a-Si/SiO2 thin films, with designed thicknesses, deposited on Si wafers. The a-Si nanodisk arrays released by selective removal of the (sacrificial) SiO2 layer remain on the Si surface due to van der Waal’s forces. In CL, monolayer coverage of hexagonally close-packed silica particles was typically obtained over a few mm2. Fluorine based RIE of the SiO2 colloidal particles is used for controlled size-reduction of the particles to obtain the desired nanodisk diameters. The vertical layer design and the gas flow rates in the dry-etch process are optimized to obtain the desired disk shape. A simple procedure for embedding the substrate-free disks in PDMS was developed.

Both a-Si nanodisk arrays on Si-substrate and those embedded in PDMS films were optically characterized by determining the reflection and transmission spectra using a spectrophotometer, equipped with an integrating sphere. The obtained optical spectroscopy results for the fabricated a-Si nanodisk arrays are in good agreement with the simulation results. Thus, it can be concluded that substrate-free a-Si nanodisk arrays in both remnant and embedded configurations were successfully obtained. Lastly, transfer printing of the nanodisk arrays using a PDMS stamp was also tested. The latter approach was also studied for micro-sized structures of different shapes, sizes and periods. These arrays of micro-sized shapes, e.g., disks, squares and rectangles were fabricated using photolithography for which a separate mask was designed. Although preliminary results are promising, extensive investigations are required to obtain high yield and high fidelity transfer printing methods.

Place, publisher, year, edition, pages
2015. , 62 p.
Series
TRITA-ICT-EX, 2015:248
Keyword [en]
Nanotechnology, Nanophotonics, Silicon, Amorphous Silicon, Nanodisk, Mie resonators, Colloidal lithography, Photolithography, Transfer printing, Dry etching, Wet etching, FDTD simulation, Optical Spectroscopy.
National Category
Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-210318OAI: oai:DiVA.org:kth-210318DiVA: diva2:1118260
Subject / course
Microelectronics and Applied Physics
Educational program
Master of Science - Nanotechnology
Examiners
Available from: 2017-06-30 Created: 2017-06-30 Last updated: 2017-06-30Bibliographically approved

Open Access in DiVA

No full text

By organisation
School of Information and Communication Technology (ICT)
Nano Technology

Search outside of DiVA

GoogleGoogle Scholar

Total: 3 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf