Quantum cascade laser element

A quantum cascade laser element comprising:

• a semiconductor superlattice structure sandwiched between a pair of conductive sections, wherein,
• the semiconductor superlattice structure is an active region that emits electromagnetic waves of a certain wavelength in the near-infrared range under an external voltage applied through the pair of conductive sections during operation,
• the active region has a plurality of unit structures that are stacked, one on top of the other,
• each unit structure includes four well layers of a composition of AlxGa1−xN separated from each other by a barrier layer of a composition of AlyGa1−yN with 0≤x<y≤1, with one of the well layers being a maximum thickness well layer that is thicker than the others, and
• both of the conductive sections in the pair of conductive sections have a refractive index lower than a refractive index of the active region for electromagnetic waves of the wavelength.