Charge carrier effect on the microwave losses observed on traveling-wave electrodes used in electro-optic modulators

The free charge carrier effect is used to explain and model microwave losses observed in traveling-wave electrodes used in electro-optic modulators when the coplanar waveguide (CPW) electrodes are fabricated on unintentionally doped heterostructure optical ridge waveguides. Microwave losses were measured between 45 MHz and 40 GHz 10(18)/cm(3) using both epitaxially grown and ion implanted semi-insulating (SI) GaAs substrates. Results show that there is a critical residual doping limit at N-d approximate to 1 x 10(14)/cm(3), above which the microwave loss increases linearly with doping for 6 mu m thick epitaxially grown materials. (C) 1998 John Wiley & Sons, Inc.