A photodetector having a small form factor and having high detection efficiency with respect to both visible light and infrared rays may include a first electrode, a collector layer on the first electrode, a tunnel barrier layer on the collector layer, a graphene layer on the tunnel barrier layer, an emitter layer on the graphene layer, and a second electrode on the emitter layer. The photodetector may be included in an image sensor. An image sensor may include a substrate, an insulating layer on the substrate, and a plurality of photodetectors on the insulating layer. The photodetectors may be aligned with each other in a direction extending parallel or perpendicular to a top surface of the insulating layer. The photodetector may be included in a LiDAR system.