Photodetector and beating spectroscopy device

A photodetector comprising:

• a semiconductor substrate including a major surface;
• a mesa portion that includes an active layer in which absorption regions that absorb detection light through intersubband absorption and transport regions that transport electrons excited by the intersubband absorption are alternately stacked, and that is formed on the major surface of the semiconductor substrate to extend along an optical waveguide direction;
• a first contact layer formed on a surface of the mesa portion on a side opposite to the semiconductor substrate;
• a second contact layer formed between the major surface of the semiconductor substrate and the mesa portion;
• a first electrode formed on the major surface of the semiconductor substrate;
• and
• an air bridge wiring electrically connected to the first contact layer and the first electrode,
• wherein when viewed in a direction perpendicular to the major surface of the semiconductor substrate, a length of the mesa portion in the optical waveguide direction is longer than a length of the mesa portion in a direction perpendicular to the optical waveguide direction,
• the air bridge wiring is led out from the first contact layer to one side in the direction perpendicular to the optical waveguide direction, and is bridged between the first contact layer and the first electrode,
• the air bridge wiring includes a bridge portion extending only in air, and
• a length of the bridge portion in the optical waveguide direction is longer than a length of the bridge portion in the direction perpendicular to the optical waveguide direction and parallel to the major surface of the semiconductor substrate.