An image sensor includes a photo sensitive device and at lest one transistor such as a drive transistor for converting charge accumulated by the photo sensitive device into an electrical signal. That at least one transistor includes a channel region comprised of a plurality of differently doped regions that generates a conduction band offset in the channel region. Such a conductive band offset increases electron mobility in the channel region for minimizing charge trapping at an interface between a gate dielectric and the semiconductor substrate for minimizing flicker noise.