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Abstract:Near-IR Evanescent-Wave Cavity Ring-Down Spectroscopy (EW-CRDS) has been applied to study the defect evolution in an a-Si:H thin film subjected to a directed beam of atomic H with a flux of (0.4-2) x 10 14 cm -2 s -1 . To this end a 42 ± 2 nm a-Si:H film was grown on the Total Internal Reflection (TIR) surface of a folded miniature optical resonator by Hot-Wire Chemical Vapor Deposition (HW-CVD). A fully reversible defect creation process is observed, with a non-linear dependence on H flux, with a time resolution of 33 ms and a relative sensitivity of 10 -7 . Through the use of polarizing optics the CRDS signal was split into s-and p-polarized components, which, combined with E-2 field calculations, provides depth sensitivity. Extensive kinetic modeling of the observed process is used to determine rate constants for the hydrogen-material interactions and defect formation in a-Si:H, as well as revealing a high diffusion coefficient for atomic H on the order of 10 -11 cm 2 s -1 . A novel reaction pathway is proposed whereby H inserted into weak Si-Si bonds recombines with mobile H, resulting in a limited penetration depth for atomic H from the gas-phase on the order of 10 -15 nm.3

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