<title>Charge transport and the mechanism for solid state film diffusion in integrated optical waveguide glass substrates</title>

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A model describing the mechanism of solid-state film diffusion into oxide substrates was developed and shown to accurately predict the dopant concentration profiles1 . The model coupled oxidation of the dopant at the metal-substrate interface with field assisted diffusion of the resulting metal ions into the substrate. The model, an adequate description of the process once initiated, could not explain how the diffusion process starts nor the experimental behavior observed at low electric fields (< 25 V/cm). This current work investigates the initiation of solid-state film ion exchange (Ag+ Na+) in glass substrates. In this paper we establish the fundamental space charge origin of the initiation process and show how this space charge gives rise to the Mott potential necessary for initiating the oxidation of the metal dopant. A one-dimensional, charge transport model is presented considering the development of space-charge effects in glass having two charge-blocking electrodes. The model results indicate that the rate limiting step for initiating Ag+ diffusion in glass is the motion of oxygen ions towards the silver anode. The predictions of this model compare favorably with the "dead times" observed in the current vs. time curves during ion-exchange. The dead time corresponds to the accumulation oxygen ions at the metal-glass interface and consequently, a period of negligible diffusion of silver into the glass. The absence of silver diffusion during this period was confirmed by analyzing the surface composition of the glass using Rutherford backscattering analysis (RBS).