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

A quantum cascade laser element comprising:

• a semiconductor substrate;
• a semiconductor laminate formed on the semiconductor substrate to include an active layer having a quantum cascade structure and to have a first end surface and a second end surface facing each other in a light waveguide direction;
• a first electrode formed on a surface on an opposite side of the semiconductor laminate from the semiconductor substrate;
• a second electrode formed on a surface on an opposite side of the semiconductor substrate from the semiconductor laminate;
• and
• an anti-reflection film formed on the first end surface,
• wherein the semiconductor laminate is configured to oscillate laser light having a center wavelength of 7.5 μm or more,
• the anti-reflection film includes an insulating film being a CeO2 film formed on the first end surface, a first refractive index film being a YF3 film or a CeF3 film disposed on a side opposite the first end surface with respect to the insulating film, and a second refractive index film formed on the first refractive index film on a side opposite the first end surface with respect to the first refractive index film and having a refractive index of larger than 1.8,
• the anti-reflection film further includes an intermediate film disposed between the insulating film and the first refractive index film,
• the intermediate film is a ZnS film formed on the insulating film,
• the first refractive index film is a YF3 film formed on the intermediate film, and
• the second refractive index film is a ZnS film.

A quantum cascade laser element comprising:

• a semiconductor substrate;
• a semiconductor laminate formed on the semiconductor substrate to include an active layer having a quantum cascade structure and to have a first end surface and a second end surface facing each other in a light waveguide direction;
• a first electrode formed on a surface on an opposite side of the semiconductor laminate from the semiconductor substrate;
• a second electrode formed on a surface on an opposite side of the semiconductor substrate from the semiconductor laminate;
• and
• an anti-reflection film formed on the first end surface,
• wherein the semiconductor laminate is configured to oscillate laser light having a center wavelength of 7.5 μm or more,
• the anti-reflection film includes an insulating film being a CeO2 film formed on the first end surface, a first refractive index film being a YF3 film or a CeF3 film disposed on a side opposite the first end surface with respect to the insulating film, and a second refractive index film formed on the first refractive index film on a side opposite the first end surface with respect to the first refractive index film and having a refractive index of larger than 1.8,
• the anti-reflection film further includes an intermediate film disposed between the insulating film and the first refractive index film,
• the intermediate film is a ZnS film formed on the insulating film,
• the first refractive index film is a CeF3 film formed on the intermediate film, and
• the second refractive index film is a ZnS film.