Experiments were conducted with an EFM (Electrostatic Force Microscope) to measure surface potential distribution on CTL (Carrier Transport Layer) having two different charge mobility characteristics. One CTL has lower charge mobility characteristic and other CTL has higher charge mobility characteristic. Four electrodes were placed on each CTL with 100 micrometers and 200 micrometers separation respectively. We had a detector of the EFM scan over three electrodes to measure surface potential distribution on the surface of each CTL. We applied a known voltage on two electrodes and remaining electrodes were connected to ground. We consequently could observe significant surface voltage fluctuation real time basis on both CTL films. The substantial fluctuation of surface voltage distribution could explain charge migration in CTL toward horizontal direction, which is perpendicular to applied electric field. The thickness of each CTL was only 5 micrometer therefore the electric field which was perpendicular to the CTL films was supposed to be very strong and uniform.