Patent ID: 6984840

Claim:
An optical semiconductor device, comprising: a substrate of SiC having a first conductivity type; a buffer layer of AlGaN formed on said substrate epitaxially, said buffer layer having said first conductivity type and a composition represented by a compositional parameter x as Al x Ga 1-x N; a first cladding layer having said first conductivity type, said first cladding layer being formed on said buffer layer epitaxially; an active layer formed epitaxially on said first cladding layer; a second cladding layer having a second, opposite conductivity type, said second cladding layer being formed on said active layer epitaxially; a first electrode provided so as to inject first-type carriers having a first polarity into said second cladding layer; and a second electrode provided on a bottom surface of said substrate so as to inject second-type carriers having a second polarity, said buffer layer containing said second type carriers with a concentration level in the range from 3×10 18 cm −3 to 1×10 20 cm −3 and said compositional parameter x larger than 0 but smaller than 0 4 (0<x<0 4) so as to reduce an interface resistance between said substrate and said buffer layer.