The electrodes in a carrier-injection-based digital optical switch are separated by a gap of less than 1 μm. Good switch performance requires minimal current spreading and effective electrical isolation of these two electrodes without perturbing the underlying guided optical fields. Two methods of such isolation are modeled and experimentally compared. One is the etching of an e-beam-defined 0.5-μm -wide trench down to an etch stop layer, and the other is the implanting of oxygen ions using the electrodes as a shadow mask. Electrical simulation results suggest that injected current magnitudes and carrier concentration profiles are similar with both the trench and the ion implant, and so they should be equally effective in preventing current flow between the two branches. However, experimental results show that ion implantation produces better switching contrasts of greater than 20 dB. We attribute this to the fact that implantation using the electrodes as a shadow mask results in an injected carrier distribution that more accurately reproduces the shape of the overlying electrode.

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Journal Journal of Vacuum Science and Technology A
Ng, S., Abdalla, S., Syrett, B, Barrios, P., McKinnon, W.R., Delâge, A., … Lapointe, J. (2006). Electrical isolation of electrodes with submicron separation in a digital optical switch. Journal of Vacuum Science and Technology A, 24(3), 807–811. doi:10.1116/1.2167976