Semiconductor laser having a doped surface zone

DETAILED DESCRIPTION What is claimed is: 1.
A semiconductor laser having a semiconductor body comprising a resonator and a first passive semiconductor layer of a first coductivity type, an active semiconductor layer on said first layer, a second passive semiconductor layer of the second opposite conductivity type on the active layer, a strip-shaped semiconductor contact layer of the second conductivity type on the second passive layer, and contact means for applying a voltage in the forward direction between the contact layer and the first passive layer to generate coherent electromagnetic radiation in a strip-shaped part of the active layer underlying the contact layer within said resonator, the passive layers having a smaller refractive index for the generated radiation than the active layer, a doped surface zone of the second conductivity type which extends over at least part of the thickness of the contact layer and extends in the second passive layer adjacent the contact layer, said surface zone having a higher doping concentration than that of the second passive layer, the doped surface zone extending adjacent the contact layer over only a part of the thickness of the second passive layer, the distance between the surface zone and the active layer being such that the effective refractive index for said generated electromagnetic radiation in the layer structure at the center of the contact layer is larger by an amount equal to at least 0.
0005 and at most 0.
005 than the effective refractive index in the layer structure adjacent the contact layer at the area of the doped surface zone.
2.
A semiconductor laser as claimed in claim 1, characterized in that the thickness of the active layer is between a minimum thickness of 0.
05 .
mu.
m with an associated maximum value of 0.
5 .
mu.
m for the distance adjacent the contact layer between the doped surface zone and the active layer and an associated minimum value of 5.
times.
10.
sup.
18 atoms per cm.
sup.
3 for the average doping concentration of the surface zone, and a maximum thickness of 0