The migration of charge carriers in response to a pulsed electric field was investigated on the 100-nm length scale and microsecond time scale by a recently introduced method employing photoluminescence detection and near field optical excitation through a sharpened optical fiber. A metal coating on the near field probe serves as a similar to 100 nm diameter electrode which acts to either collect or repel majority charge carriers, depending on the sign of the applied voltage. The local carrier density is determined by carrier-induced photoluminescence quenching. The transient response is described by a model including carrier drift and diffusion. The role of oxygen in photoinduced carrier generation, exciton quenching, and charge trapping is also investigated.