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Infrared and temperature programmed desorption spectroscopy analysis of glow discharge hydrogenated amorphous silicon (a-Si:H) thin film

Santjojo, D.J. Djoko Herry (1995) Infrared and temperature programmed desorption spectroscopy analysis of glow discharge hydrogenated amorphous silicon (a-Si:H) thin film. Masters by Research thesis, Murdoch University.

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Amorphous silicon technology offers an avenue for low-cost thin film photovoltaic applications. The performance of solar cells based on amorphous silicon alloy is limited by light-induced degradation. Inadequate description of the microstructure of this material hampers the solution of this problem.

This present study investigated the role of hydrogen in the performance of intrinsic hydrogenated amorphous silicon (a-Si:H) thin film and the effect of prolonged illumination on the material.

The a-Si:H films were prepared by plasma enhanced chemical vapour deposition. They were characterised by using Fourier transform infrared spectroscopy (FTIR) and temperature programmed desorption spectroscopy (TPDS). This work categorized silicon-hydrogen bonding found in the a-Si:H network into four groups: Si-H group, Si=H2 group, (Si=H2)n group, and Si=H3 group. The desorption experiments at temperature of 350 °C, 450 °C and 575 °C with subsequent infrared measurements relate the peaks found in the TPD spectra with silicon-hydrogen bonding vibrations in the infrared spectra. The weakly bonded hydrogen (WBH) and the tightly bonded hydrogen of other previous workers have been analyzed in term of silicon-hydrogen groups.

This work also investigated the effect on these factors of the variation of three major deposition parameters. These were substrate temperature, rf-power, and chamber pressure. The substrate temperature was varied from 100 °C to 275 °C, the RF-power was varied from 2 watts to 4 watts, and the chamber pressure was varied from 0.08 mbar to 0.8 mbar.

In order to describe the hydrogen motion during prolonged illumination a model was devised based on the results of the infrared spectra of samples which were introduced to light soaking up to 366 hours (two weeks). The model predicts the breaking of both Si-Si and Si-H bonds. Two mechanisms of the breaking bonds and the hydrogen motion were considered: on the surface and in the bulk. From the model it can be seen that during the light soaking the hydrogen from the bulk and the hydrogen from the surface were accumulated at the region near the surface. The dangling bonds created during the light soaking seem to move into the bulk. The subsequent annealing restored the dangling bonds into Si-H bonds.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation(s): School of Physical Sciences, Engineering and Technology
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Cornish, John
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