Novel in situ and real-time optical probes to detect (surface) defect states of a-Si:H

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Abstract

This paper describes two novel optical diagnostics that were recently introduced to the field of Si-based thin films, in particular for probing defect states present in the bulk and at the surface of a-Si:H films. It is expected that these diagnostics, when applied in situ or real time during film growth, can provide new insights into the a-Si:H film properties as well as into the fundamental surface processes during growth. The first method is cavity ringdown spectroscopy (CRDS). From ex situ measurements on a-Si:H thin films, it is shown that this method is very powerful for measuring absolute defect-related absorptions at subgap energies without the need for a calibration procedure, even for films as thin as 4 nm. It is also shown that the method can be used for measuring rare-earth dopants – here Er3+ in silicon-rich oxide – to the extent that issues about absorption cross-sections can be resolved by using thin samples instead of waveguides. Furthermore, the in situ application of the method for thin films is discussed by presenting the evanescent-wave cavity ringdown (EW-CRDS) technique. The second method is spectroscopic second harmonic generation (SHG). It has been found that this non-linear optical technique yields a photon energy dependent signal for as-deposited a-Si:H films and that this signal has a contribution from a-Si:H surface states. From a comparison with c-Si surface science studies, the possible origin of the signal from surface Si dangling bonds and strained Si-Si bonds is discussed. The application of SHG during real-time film growth is also presented.
Original languageEnglish
Title of host publicationAmorphous and nanocrystalline silicon science and technology - 2005 : symposium held March 28 - April 1, 2005, San Francisco, California, U.S.A.
EditorsR.W. Collins, P. Craig Taylor, M. Kondo
Place of PublicationWarrendale
PublisherMaterials Research Society
Pages19-30
ISBN (Print)1-55899-815-2
DOIs
Publication statusPublished - 2005

Publication series

NameMaterials Research Society Symposium Proceedings
PublisherMaterials Research Society
Volume862
ISSN (Print)0272-9172

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