Semiconductor laser or intensifier

A semiconductor device for operation with coherent electromagnetic radiation, comprising a semiconductor body having an active semiconductor layer which comprises a p-n junction and which is bounded on either side by first and second passive semiconductor layers having a lower refractive index for said radiation than the active layer, means for supplying current to a strip-shaped region of the active layer in a direction substantially perpendicular to the layer, at least a selected one of said passive layers comprising a strip-shaped zone, the projection of said zone onto said strip-shaped region of the active layer extending fully within said strip-shaped region and said zone having a different structure from that of the adjacent parts of said selected passive layer, said strip-shaped zone having a width which is at most equal to that of said strip-shaped region of the active layer, the active layer having a substantially constant thickness, at least said selected passive layer comprising a first portion having a refractive index n.sub.1 and a second portion having a refractive index n.sub.2 different from n.sub.1 for said radiation, said second portion having the same conductivity type as the first portion, the active layer adjoining said first portion at least within said strip-shaped zone, and said device satisfying the condition

• (n.sub.1 -n.sub.2)(d.sub.1 -d.sub.2)>0,
• wherein d.sub.1 is the thickness of that part of the first portion measured from the active layer to the closest part of the second portion within the strip-shaped zone, and d.sub.2 is the thickness of the first portion in the region of said selected passive layer adjoining and outside the strip-shaped zone.