Semiconductor laser

A semiconductor laser comprising:

• a substrate having a principal surface;
• a mesa structure disposed on the principal surface of the substrate, the mesa structure extending in a direction parallel to the principal surface, the mesa structure including an active region, the active region including a quantum well structure, the active region having a top surface, a bottom surface facing the top surface, and side surfaces;
• a first cladding layer having a refractive index lower than that of the active region, the first cladding layer being in contact with the top surface of the active region, the first cladding layer having an opening;
• a second cladding layer having a refractive index lower than that of the active region, the second cladding layer covering the bottom surface of the active region except for a bottom center portion thereof;
• an emitter region including a first semiconductor region of a first conductivity type on the top surface of the active region, the first semiconductor region being in contact with the top surface inside the opening of the first cladding layer so as to supply carriers to the active region;
• a collector region including a second semiconductor region of the first conductivity type on at least one side surface of the active region, the second semiconductor region being in contact with the at least one side surface so as to receive the carriers from the active region;
• and
• a third semiconductor region of the first conductivity type on the bottom surface of the active region, the third semiconductor region being in contact with the bottom center portion of the bottom surface of the active region and the principal surface of the substrate, wherein
• the active region emits light by the carriers transiting in the active region,
• the collector region is separated from the emitter region by the first cladding layer being therebetween on the mesa structure,
• the top surface and the bottom surface of the active region extend in planes parallel to the principal surface, and
• the second semiconductor region is disposed on the at least one side surface of the active region and extends along a plane perpendicular to the principal surface of the substrate.