Semiconductor laser

Abstract

A semiconductor laser includes: a stacked body having an active layer including a quantum well layer, the active layer having a cascade structure including a first region capable of emitting infrared laser light with a wavelength of not less than 12 μm and not more than 18 μm by an intersubband optical transition of the quantum well layer and a second region capable of relaxing energy of a carrier alternately stacked, the stacked body having a ridge waveguide and being capable of emitting the infrared laser light; and a dielectric layer provided so as to sandwich both sides of at least part of side surfaces of the stacked body, a wavelength at which a transmittance of the dielectric layer decreases to 50% being 16 μm or more, the dielectric layer having a refractive index lower than refractive indices of all layers constituting the active layer.

1 . A semiconductor laser comprising:
 a stacked body disposed on an InP or GaAs substrate having an active layer including a quantum well layer the active aver having a cascade structure including a first region capable of emitting infrared laser light by an intersubband optical transition of the quantum well layer and a second region capable of relaxing energy of a carrier injected from the first region alternately stacked, the stacked body having a ridge waveguide and being capable of emitting the infrared laser light in a direction along which the ridge waveguide extends; and   a dielectric layer provided so as to sandwich at least both sides of the active layer of the stacked body in a cross section, the dielectric layer having a refractive index lower than refractive indices of all lavers constituting the active layer, the dielectric layer being made of at least one single-crystal material of thallium bromoiodide, thallium bromochloride, ZnSe, CdTe, and diamond formed directly on the InP or GaAs substrate and including neither acceptors nor donors at a region adjacent to the side surfaces of the active layer.   
     
     
         2 . The semiconductor laser according to  claim 1 , further comprising a first electrode connected to the ridge waveguide. 
     
     
         3 . The semiconductor laser according to  claim 1 , further comprising an insulating film covering a surface of the dielectric layer. 
     
     
         4 . The semiconductor laser according to  claim 1 , wherein the second region has a plurality of minibands. 
     
     
         5 . The semiconductor laser according to  claim 1 , wherein
 an extraction barrier layer is provided between the first region and the second region and   an injection barrier layer is provided between the second region and the first region.   
     
     
         6 . The semiconductor laser according to  claim 1 , wherein a diffraction grating is provided in the stacked body in the direction along which the ridge waveguide extends. 
     
     
         7 . The semiconductor laser according to  claim 6 , wherein a pitch of the diffraction grating is one half of an in-medium wavelength. 
     
     
         8 . The semiconductor laser according to  claim 1 , wherein
 the ridge waveguide has a first end surface and a second end surface on an opposite side of the first end surface,   a first reflection film is provided at the first end surface, and   a second reflection film having a reflectance higher than a reflectance of the first reflection film is provided at the second end surface.   
     
     
         9 . The semiconductor laser according to  claim 1 , wherein the carrier is an electron. 
     
     
         10 . The semiconductor laser according to claim.  1 , wherein the active layer contains GaAs and Al x Ga 1−x As (0<x<1). 
     
     
         11 . The semiconductor laser according to  claim 1 , wherein the active layer contains In y Ga 1−y As (0<y<1) and Al z In 1−z As (0<z<1).