Patent ID: 6990131

Claim:
A semiconductor optical device comprising: a multilayer structure formed mesa-stripe-like constituted by a first cladding layer having an n-type conductivity, an active region formed from an active layer or photoabsorption layer, and a second cladding layer having a p-type conductivity which are successively formed on a semiconductor substrate having a first crystallographic orientation; and buried layers which are made of a ruthenium-doped semi-insulating semiconductor crystal and formed on two sides of said mesa-stripe-like multilayer structure; wherein a first electrically activated ruthenium concentration in the ruthenium-doped semi-insulating semiconductor crystal grown on the growth surface having a second crystallographic orientation which is formed in the process of growing the semi-insulating semiconductor crystal is substantially equal to or higher than a second electrically activated ruthenium concentration in the ruthenium-doped semi-insulating semiconductor crystal grown on the growth surface having first crystallographic orientation; and the second crystallographic orientation is different from the first crystallographic orientation.