Quantum cascade laser

A quantum cascade laser comprising:

• a substrate including a principal surface, a back surface, and a substrate end face, the principal surface and the back surface being arranged in a first direction, the principal surface being opposite to the back surface, the substrate end face extending along a reference plane intersecting a second direction, and the second direction intersecting the first direction;
• a semiconductor laminate disposed on the principal surface of the substrate, the semiconductor laminate having a laminate end face, and the semiconductor laminate including a core layer extending from the laminate end face in the second direction, and a cladding layer disposed on the core layer, and the laminate end face extending along the reference plane;
• a first electrode disposed on the semiconductor laminate, the semiconductor laminate being disposed between the first electrode and the substrate;
• a second electrode disposed on the back surface of the substrate;
• a first insulating film disposed on the laminate end face, the substrate end face, and the first electrode;
• a metal film disposed on the first insulating film, on the laminate end face, on the substrate end face, and on the first electrode;
• and
• a second insulating film disposed on the first electrode, the second insulating film having a part on the first electrode, and the part of the second insulating film being between the metal film and the semiconductor laminate,
• on the first electrode, the second insulating film having a thickness in the first direction larger than that of the first insulating film.