Light detection module and beat spectrometer

A photodetection module comprising:

• a photodetector;
• and
• a fixing member to which the photodetector is fixed,
• wherein the photodetector includes:
• a semiconductor substrate including a major surface,
• a mesa portion including a semiconductor region that generates an electrical signal in accordance with an incident amount of detection light, and formed on the major surface of the semiconductor substrate,
• 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, and
• a first electrode formed in a planar shape on the major surface of the semiconductor substrate, and electrically connected to one of the first contact layer and the second contact layer,
• the fixing member includes:
• an insulating substrate including a major surface, and
• a first wiring formed in a planar shape on the major surface of the insulating substrate,
• a recessed portion is formed in the major surface of the insulating substrate,
• at least a part of the mesa portion is disposed inside the recessed portion, and
• the first electrode is electrically connected to the first wiring in a state where the first electrode is in surface contact with the first wiring,
• wherein both side surfaces of the mesa portion in a direction perpendicular to an optical waveguide direction are exposed.

A beating spectroscopy device comprising:

• a fixed wavelength light source;
• a variable wavelength light source;
• and
• a photodetection module that detects light from the fixed wavelength light source and light from the variable wavelength light source as detection light,
• the photodetection module comprising:
• a photodetector;
• and
• a fixing member to which the photodetector is fixed,
• wherein the photodetector includes:
• a semiconductor substrate including a major surface,
• a mesa portion including a semiconductor region that generates an electrical signal in accordance with an incident amount of the detection light, and formed on the major surface of the semiconductor substrate,
• 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, and
• a first electrode formed in a planar shape on the major surface of the semiconductor substrate, and electrically connected to one of the first contact layer and the second contact layer,
• the fixing member includes:
• an insulating substrate including a major surface, and
• a first wiring formed in a planar shape on the major surface of the insulating substrate,
• a recessed portion is formed in the major surface of the insulating substrate,
• at least a part of the mesa portion is disposed inside the recessed portion, and
• the first electrode is electrically connected to the first wiring in a state where the first electrode is in surface contact with the first wiring,
• wherein the light from the fixed wavelength light source and the light from the variable wavelength light source are detected by the photodetector while a wavelength of the light from the variable wavelength light source is changed to scan a frequency of a beating signal having a frequency in accordance with a wavelength difference between the light from the fixed wavelength light source and the light from the variable wavelength light source.