| 摘要 |
A quantum cascade laser includes a semiconductor substrate, and an active layer which is provided on the semiconductor substrate, and has a cascade structure in which unit laminate structures 16 having quantum well emission layers 17 and injection layers 18 are laminated in multiple stages. Further, the quantum cascade laser is configured such that the unit laminate structure 16 has an emission upper level L up , an emission lower level L low , and a relaxation miniband MB including an energy level lower than the emission lower level in its subband level structure, and light is generated by an intersubband transition of electrons from the upper level to the lower level, and the electrons after the intersubband transition are relaxed from the lower level L low to the miniband MB through LO phonon scattering, to be injected from the injection layer 18 to the latter stage emission layer via the miniband MB. Thereby, the quantum cascade laser which is capable of efficiently forming an inverted population in the quantum well emission layer, to improve its laser operation performance, is realized. |
