Reversible above band gap absorption properties of Hydrogenated amorphous silicon (a-Si:H)

Research output: Contribution to conferencePosterAcademic

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Abstract

The vast majority of Staebler-Wronski Effect(SWE) studies have been focused on understanding the nature of metastable defects in hydrogenated amorphous silicon(a-Si:H), i.e. the optoelectrical properties for photon energies below the bandgap. However, the effects of prolonged light exposure and annealing on the optoelectrical properties above the bandgap have not been thoroughly investigated. For photonic integrated circuits even refractive index changes as little as 1%, may have a significant impact. Therefore, this work aims to study possible changes in the absorption properties above the bandgap as enabled by high intensity visible light soaking and annealing. The parameter used in this work to study such changes in absorption is the imaginary part of the pseudo dielectric function <e2> derived by spectroscopic ellipsometric (SE) measurements. A set of a-Si:H films was deposited near the amorphous/nanocrystalline phase transition at different substrate temperatures having different microstructures by inductively coupled plasma enhanced chemical vapour deposition(ICP-PECVD). For an a-Si:H film the <e2> value exhibits considerable change over time, as the top surface undergoes oxidation during prolonged air exposure. Therefore, the light-induced and annealing effects on these samples are investigated with respect to the corresponding twin samples that are stored at room temperature in air to serve as a reference. The measured <e2> values around the electronic polarization resonance clearly decrease after light soaking and can be completely reversed after annealing (nearly 4%; see attached figures), indicating familiar metastable nature of defects in hydrogenated amorphous silicon. Since no loss of bonded hydrogen is detected after repeated light soaking and annealing cycles and considering the reversibility of the <e2> change, it is believed that a change in the bulk optical properties is the main contributor to the observed metastable effect suggesting reversible refractive index change. Optical simulations which take the sample surface oxidation into account suggest that the effect may be explained through metastable volumetric expansion.
Original languageEnglish
Publication statusPublished - 21 Aug 2017
Event27th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2017) - Seoul National university, Seoul, Korea, Republic of
Duration: 21 Aug 201725 Aug 2017
Conference number: 27
http://tft.khu.ac.kr/icans2017/index.html

Conference

Conference27th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2017)
Abbreviated titleICANS (2017)
CountryKorea, Republic of
CitySeoul
Period21/08/1725/08/17
Internet address

Fingerprint

Amorphous silicon
amorphous silicon
soaking
Energy gap
Annealing
annealing
Refractive index
refractivity
air
Inductively coupled plasma
Air
Photonics
integrated circuits
Integrated circuits
Hydrogen
Photons
Optical properties
Phase transitions
photonics
Polarization

Keywords

  • Hydrogenated amorphous silicon
  • spectroscopic ellipsometry
  • metastable optical properties
  • refractive index

Cite this

Mohammed, M. A., Melskens, J., Stabile, R., Kessels, W. M. M., & Raz, O. (2017). Reversible above band gap absorption properties of Hydrogenated amorphous silicon (a-Si:H). Poster session presented at 27th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2017), Seoul, Korea, Republic of.
Mohammed, M.A. ; Melskens, J. ; Stabile, R. ; Kessels, W.M.M. ; Raz, O. / Reversible above band gap absorption properties of Hydrogenated amorphous silicon (a-Si:H). Poster session presented at 27th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2017), Seoul, Korea, Republic of.
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title = "Reversible above band gap absorption properties of Hydrogenated amorphous silicon (a-Si:H)",
abstract = "The vast majority of Staebler-Wronski Effect(SWE) studies have been focused on understanding the nature of metastable defects in hydrogenated amorphous silicon(a-Si:H), i.e. the optoelectrical properties for photon energies below the bandgap. However, the effects of prolonged light exposure and annealing on the optoelectrical properties above the bandgap have not been thoroughly investigated. For photonic integrated circuits even refractive index changes as little as 1{\%}, may have a significant impact. Therefore, this work aims to study possible changes in the absorption properties above the bandgap as enabled by high intensity visible light soaking and annealing. The parameter used in this work to study such changes in absorption is the imaginary part of the pseudo dielectric function derived by spectroscopic ellipsometric (SE) measurements. A set of a-Si:H films was deposited near the amorphous/nanocrystalline phase transition at different substrate temperatures having different microstructures by inductively coupled plasma enhanced chemical vapour deposition(ICP-PECVD). For an a-Si:H film the value exhibits considerable change over time, as the top surface undergoes oxidation during prolonged air exposure. Therefore, the light-induced and annealing effects on these samples are investigated with respect to the corresponding twin samples that are stored at room temperature in air to serve as a reference. The measured values around the electronic polarization resonance clearly decrease after light soaking and can be completely reversed after annealing (nearly 4{\%}; see attached figures), indicating familiar metastable nature of defects in hydrogenated amorphous silicon. Since no loss of bonded hydrogen is detected after repeated light soaking and annealing cycles and considering the reversibility of the change, it is believed that a change in the bulk optical properties is the main contributor to the observed metastable effect suggesting reversible refractive index change. Optical simulations which take the sample surface oxidation into account suggest that the effect may be explained through metastable volumetric expansion.",
keywords = "Hydrogenated amorphous silicon, spectroscopic ellipsometry, metastable optical properties, refractive index",
author = "M.A. Mohammed and J. Melskens and R. Stabile and W.M.M. Kessels and O. Raz",
year = "2017",
month = "8",
day = "21",
language = "English",
note = "27th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2017), ICANS (2017) ; Conference date: 21-08-2017 Through 25-08-2017",
url = "http://tft.khu.ac.kr/icans2017/index.html",

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Mohammed, MA, Melskens, J, Stabile, R, Kessels, WMM & Raz, O 2017, 'Reversible above band gap absorption properties of Hydrogenated amorphous silicon (a-Si:H)' 27th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2017), Seoul, Korea, Republic of, 21/08/17 - 25/08/17, .

Reversible above band gap absorption properties of Hydrogenated amorphous silicon (a-Si:H). / Mohammed, M.A.; Melskens, J.; Stabile, R.; Kessels, W.M.M.; Raz, O.

2017. Poster session presented at 27th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2017), Seoul, Korea, Republic of.

Research output: Contribution to conferencePosterAcademic

TY - CONF

T1 - Reversible above band gap absorption properties of Hydrogenated amorphous silicon (a-Si:H)

AU - Mohammed, M.A.

AU - Melskens, J.

AU - Stabile, R.

AU - Kessels, W.M.M.

AU - Raz, O.

PY - 2017/8/21

Y1 - 2017/8/21

N2 - The vast majority of Staebler-Wronski Effect(SWE) studies have been focused on understanding the nature of metastable defects in hydrogenated amorphous silicon(a-Si:H), i.e. the optoelectrical properties for photon energies below the bandgap. However, the effects of prolonged light exposure and annealing on the optoelectrical properties above the bandgap have not been thoroughly investigated. For photonic integrated circuits even refractive index changes as little as 1%, may have a significant impact. Therefore, this work aims to study possible changes in the absorption properties above the bandgap as enabled by high intensity visible light soaking and annealing. The parameter used in this work to study such changes in absorption is the imaginary part of the pseudo dielectric function derived by spectroscopic ellipsometric (SE) measurements. A set of a-Si:H films was deposited near the amorphous/nanocrystalline phase transition at different substrate temperatures having different microstructures by inductively coupled plasma enhanced chemical vapour deposition(ICP-PECVD). For an a-Si:H film the value exhibits considerable change over time, as the top surface undergoes oxidation during prolonged air exposure. Therefore, the light-induced and annealing effects on these samples are investigated with respect to the corresponding twin samples that are stored at room temperature in air to serve as a reference. The measured values around the electronic polarization resonance clearly decrease after light soaking and can be completely reversed after annealing (nearly 4%; see attached figures), indicating familiar metastable nature of defects in hydrogenated amorphous silicon. Since no loss of bonded hydrogen is detected after repeated light soaking and annealing cycles and considering the reversibility of the change, it is believed that a change in the bulk optical properties is the main contributor to the observed metastable effect suggesting reversible refractive index change. Optical simulations which take the sample surface oxidation into account suggest that the effect may be explained through metastable volumetric expansion.

AB - The vast majority of Staebler-Wronski Effect(SWE) studies have been focused on understanding the nature of metastable defects in hydrogenated amorphous silicon(a-Si:H), i.e. the optoelectrical properties for photon energies below the bandgap. However, the effects of prolonged light exposure and annealing on the optoelectrical properties above the bandgap have not been thoroughly investigated. For photonic integrated circuits even refractive index changes as little as 1%, may have a significant impact. Therefore, this work aims to study possible changes in the absorption properties above the bandgap as enabled by high intensity visible light soaking and annealing. The parameter used in this work to study such changes in absorption is the imaginary part of the pseudo dielectric function derived by spectroscopic ellipsometric (SE) measurements. A set of a-Si:H films was deposited near the amorphous/nanocrystalline phase transition at different substrate temperatures having different microstructures by inductively coupled plasma enhanced chemical vapour deposition(ICP-PECVD). For an a-Si:H film the value exhibits considerable change over time, as the top surface undergoes oxidation during prolonged air exposure. Therefore, the light-induced and annealing effects on these samples are investigated with respect to the corresponding twin samples that are stored at room temperature in air to serve as a reference. The measured values around the electronic polarization resonance clearly decrease after light soaking and can be completely reversed after annealing (nearly 4%; see attached figures), indicating familiar metastable nature of defects in hydrogenated amorphous silicon. Since no loss of bonded hydrogen is detected after repeated light soaking and annealing cycles and considering the reversibility of the change, it is believed that a change in the bulk optical properties is the main contributor to the observed metastable effect suggesting reversible refractive index change. Optical simulations which take the sample surface oxidation into account suggest that the effect may be explained through metastable volumetric expansion.

KW - Hydrogenated amorphous silicon

KW - spectroscopic ellipsometry

KW - metastable optical properties

KW - refractive index

M3 - Poster

ER -

Mohammed MA, Melskens J, Stabile R, Kessels WMM, Raz O. Reversible above band gap absorption properties of Hydrogenated amorphous silicon (a-Si:H). 2017. Poster session presented at 27th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2017), Seoul, Korea, Republic of.