Semiconductor optical device with a buried heterostructure (BH) having reduced parasitic capacitance and reduced inter-diffusion

A semiconductor optical device, comprising:

• a semiconductor substrate;
• a buried mesa structure formed on the semiconductor substrate, the buried mesa structure including a first n-type cladding layer, an active region above the first n-type cladding layer, and a first p-type cladding layer above the active region;
• stacked side layers on each side of the buried mesa structure, the stacked side layers including an Fe-doped current blocking layer burying the buried mesa structure on each side and a second n-type cladding layer on the Fe-doped current blocking layer;
• a second p-type cladding layer above the mesa structure and the stacked side layers, wherein the second p-type cladding layer is a highly Zn-doped layer including a concentration of Zn in a range of 5×1017 cm−3 to 3×1018 cm−3, wherein contact portions of the Fe-doped current blocking layer extend above the active region to contact the highly Zn-doped layer, and wherein the second n-type cladding layer is outside the contact portions of the Fe-doped current blocking layer and between a substantial portion of the Fe-doped current blocking layer and the highly Zn-doped layer, wherein tops of the first p-type cladding layer, the second n-type cladding layer, and the contact portions of the Fe-doped current blocking layer are flush with one another and at the same level, and wherein the contact portions of the Fe-doped current blocking layer contact the highly Zn-doped layer at a contact region that is less than 5% of the total surface area of the highly Zn-doped layer.