Image sensor devices are provided having reduced dark current generation characteristics. These image sensor devices include a semiconductor substrate and a photo-detector therein (e.g., P-N photodiode). The photo-detector includes a charge-generating region therein that is configured to convert photons received by the photo-detector into charge carriers. A first transistor, which has a terminal configured to receive the charge carriers generated by the photo-detector, is also provided. The first transistor includes a first gate electrode and a first pair of lightly doped source and drain regions of unequal width on opposite sides of the first gate electrode. This first transistor may be a three-terminal device and the terminal that is configured to receive the charge carriers may be selected from a group consisting of a gate, source and drain terminals. In particular, the first transistor may be configured as a reset transistor or as a source-follower transistor.