| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a quantum cascade layer capable of enhancing the operational performance of the laser by efficiently forming inverted distribution in a light-emitting layer. Ž<P>SOLUTION: The quantum cascade laser is composed of: a semiconductor substrate; and an active layer configured by laminating multiple stages of unit laminates 16 each of which includes a light-emitting layer 17 and an injection layer 18. A subband level structure of the unit laminate 16 includes an upper emission level L<SB>up</SB>, a lower emission level L<SB>low</SB>and relaxation miniband MB and light is generated by transition of electrons from the upper level to the lower level, between subbands. Further, electrons transited among the subbands are relaxed from the lower level L<SB>low</SB>to the miniband MB by LO phonon scattering and injected into the subsequent light-emitting layer through the miniband MB. A first barrier layer of the light-emitting layer 17 functions as an injection barrier layer, and the layer thickness of a third well layer is set within a range of 90 to 105% of the layer thickness of a second well layer. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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