Evaluation of defect-related diffusion in semiconductors by electrooptical sampling

The electrooptical sampling technique is used to assess the electrical behavior of Ohmic contact regions in GaAs. For this purpose unique Ohmic contact coplanar waveguides were fabricated and tested. A reduced electrooptical sampling signal is detected in certain Ohmic contact regions. Since the electrical fields present in this device are known a priori, the deviation of the electrooptical signal from its nominal value is attributed to a deviation in the electrooptical coefficient. Defects introduced during the annealing step of the Ohmic contact accelerated by existing dislocations are discussed as a mechanism capable of disrupting the electrooptic coefficient. A simple phenomenological diffusion model is presented to explain the mechanism responsible for the nulling of the electrooptical coefficient.