A photodetector includes a quantum dot group including a first quantum dot of a reference size and a second quantum dot of a size other than the reference size, a first resonant tunneling structure disposed on a first side of the quantum dot group and including a barrier layer, a well layer, and a barrier layer, and a second resonant tunneling structure disposed on a second side of the quantum dot group and including a barrier layer, a well layer, and a barrier layer, wherein a first resonance level of the first resonant tunneling structure and a ground level of the first quantum dot have a relationship that causes tunneling, and a second resonance level of the second resonant tunneling structure and an excited level of the first quantum dot have a relationship that causes tunneling.