Quantum cascade laser and method for manufacturing quantum cascade laser
A quantum cascade laser includes a substrate having first and second regions; a stacked semiconductor layer disposed on the second region, the stacked semiconductor layer including an active layer, the stacked semiconductor layer having a first end facet and a second end facet that constitute a laser cavity; an insulating layer disposed on the first end facet and an upper surface of the stacked semiconductor layer, the insulating layer having an opening on the upper surface; a conductive layer disposed on the insulating layer and in the opening, the conductive layer being in contact with the upper surface through the opening; and a metal layer disposed on the conductive layer on the first end facet and the upper surface. The first end facet of the stacked semiconductor layer is retreated from an end facet of the substrate to a boundary between the first and second regions.
1. A quantum cascade laser comprising:
a substrate having a first region and a second region arranged in a waveguiding direction;
a stacked semiconductor layer disposed on the second region of the substrate, the stacked semiconductor layer including an active layer, the stacked semiconductor layer having a first end facet and a second end facet that constitute a laser cavity;
an insulating layer disposed on the first end facet and an upper surface of the stacked semiconductor layer, the insulating layer having an opening on the upper surface of the stacked semiconductor layer;
a conductive layer disposed on the insulating layer and in the opening, the conductive layer being in contact with the upper surface of the stacked semiconductor layer through the opening; and
a metal layer disposed on the conductive layer on the first end facet and the upper surface of the stacked semiconductor layer,
wherein the first end facet of the stacked semiconductor layer is retreated from an end facet of the substrate to a boundary between the first region and the second region of the substrate in the waveguiding direction.
2. The quantum cascade laser according to claim 1 , wherein
the stacked semiconductor layer constitutes a semiconductor mesa extending in the waveguiding direction, and
the first end facet and the second end facet of the stacked semiconductor layer correspond to end facets of the semiconductor mesa that are opposed to each other in the waveguiding direction.
3. The quantum cascade laser according to claim 1 , wherein the first end facet of the stacked semiconductor layer with the metal layer has a reflectance of more than 70%.
4. The quantum cascade laser according to claim 1 , wherein
the metal layer is made of a gold film, and
the metal layer has a thickness of 50 nm or more.
5. The quantum cascade laser according to claim 1 , wherein the first end facet of the stacked semiconductor layer has a reflectance larger than a reflectance of the second end facet of the stacked semiconductor layer.
6. The quantum cascade laser according to claim 1 , wherein
the substrate has a third region arranged adjacent to the second region in the waveguiding direction,
the insulating layer is disposed on the second end facet of the stacked semiconductor layer,
the metal layer is disposed on the conductive layer on the second end facet of the stacked semiconductor layer,
the second end facet of the stacked semiconductor layer is retreated from another end facet of the substrate to a boundary between the second region and the third region of the substrate in the waveguiding direction, and
the metal layer disposed on the second end facet of the stacked semiconductor layer has a thickness smaller than a thickness of the metal layer disposed on the first end facet of the stacked semiconductor layer.
7. The quantum cascade laser according to claim 1 , wherein the second end facet of the stacked semiconductor layer has a cleavage surface.