Semiconductor laser and method of fabricating same

A semiconductor laser made of a III-V compound semiconductor including nitrogen, comprising:

• a substrate;
• a first-conductivity-type cladding layer made of In.sub.x Ga.sub.y Al.sub.z B.sub.1-x-y-z N (0.ltoreq.x, y, z, x+y+z.ltoreq.1) formed on or above the substrate;
• a core region formed on the first-conductivity-type cladding layer, said core region including at least an active layer;
• a second-conductivity-type cladding layer made of In.sub.x Ga.sub.y Al.sub.z B.sub.1-x-y-z N (0.ltoreq.x, y, z, x+y+z.ltoreq.1) formed on the core region;
• a double heterostructure composed of the first-conductivity-type cladding layer, the core region and the second-conductivity-type cladding layer;
• a second-conductivity-type contact layer formed on or above the second-conductivity-type cladding layer;
• a first electrode formed on the second-conductivity-type contact layer which is arranged on the second-conductivity-type cladding layer side;
• and
• a second electrode arranged on the first-conductivity-type cladding layer side, wherein a total thickness of the active layer is less than 0.05 .mu.m and an Al compositional ratio x.sub.Al of each of the cladding layers, an average In compositional ratio y.sub.In of a core region, a sum of both compositional ratios .DELTA.x (=x.sub.Al +y.sub.In), a total thickness H.sub.core of the core region and a thickness H.sub.clad of each of the cladding layers satisfy the following relation in reference to an oscillation wavelength .lambda.:
• .DELTA.x.multidot.(H.sub.core /.lambda.).multidot.(H.sub.clad /.lambda.).gtoreq.0.08.