A photodetector comprises a nanometer heterostructure, a first electrode, a second electrode, a current detection element, and a power supply; the nanometer heterostructure comprises a first carbon nanotube, a semiconductor layer, and a second carbon nanotube; the first carbon nanotube is electrically connected with the first electrode; the second carbon nanotube is electrically connected with thesecond electrode; the first and second electrodes are electrically connected with the current detection element; the power supply is electrically connected with the first electrode and the second electrode; the first electrode, the second electrode, the current detection element and the power supply form a loop structure.