Quantum cascade laser device and method for manufacturing quantum cascade laser device

A quantum cascade laser device comprising:

• a semiconductor substrate;
• a first-conductivity-type first cladding layer formed above the semiconductor substrate;
• a core region formed above the first cladding layer and comprising a plurality of stages each having an active region in which a plurality of barrier layers and a plurality of well layers are formed alternately, and an injector region configured to inject electrons into the active region;
• and
• a first-conductivity-type second cladding layer formed above the core region, wherein
• a cavity length is L, and
• a gain has a maximum gain value at a wavelength λqcl when current is injected, and
• a low-reflectivity film is provided on one end surface such that the reflectivity is minimized at a wavelength λcot configured to be separated from the wavelength λqcl by a predetermined wavelength within the wavelength range between two points in which the gain value decreases by a predetermined ratio of the maximum gain value where a wavelength width Δλqcl is defined as a wavelength width between the two points, and
• a wavelength width Δλmir between two points where the mirror loss value is generated by subtracting a predetermined loss value from the maximum mirror loss value calculated from the reflectivity Rr of the other end surface and the cavity length L is set such that the wavelength width Δλmir is smaller than the wavelength width Δλqcl.