High-electric-field poling of nonlinear optical polymers

We have investigated electrical conduction phenomena during high-electric-field poling of a standard covalently functionalized DR-1 side-chain polymer. We performed electric current and second-harmonic measurements simultaneously to derive the effective internal field strength. Various metals and transparent indium tin oxide were used as electrodes. Current densities appeared to he interface (electrode) limited, with little dependence on the work function of the metal for the top electrode (Bardeen barrier at the electrode-dielectric interface), whereas for the bottom electrode-dielectric interface a dependence on the work function of the metal was observed. The field dependence of the current density was found to be Schottky charge emission for medium field strengths (E-POL less than or equal to 100 V/mu m), whereas it was dominated by Fowler-Nordheim tunneling at higher poling fields. In the presence of an additional inorganic barrier layer, significant suppression of tunneling was observed, which led to a reduced probability of singular breakdown events and shifted the limit of avalanche breakdown to higher internal effective poling field strengths. (C) 1998 Optical Society of America.