Quantum cascade semiconductor laser

A quantum cascade semiconductor laser comprising:

• a substrate formed of an n-type semiconductor, the substrate having a main surface;
• a mesa waveguide disposed on the main surface of substrate, the mesa waveguide including a core layer and an n-type upper cladding layer, the core layer being disposed between the main surface of the substrate and the n-type upper cladding layer;
• a first semiconductor layer disposed on a side surface of the mesa waveguide and the main surface of the substrate, the first semiconductor layer being in contact with the side surface of the mesa waveguide;
• and
• a second semiconductor layer disposed on the first semiconductor layer,
• wherein the first semiconductor layer and the second semiconductor layer constitute a burying region embedding the side surfaces of the mesa waveguide,
• the first semiconductor layer is formed of at least one of a semi-insulating semiconductor and a p-type semiconductor, and
• the second semiconductor layer is formed of an n-type semiconductor.