Optical semiconductor device

An optical semiconductor device, comprising:

• a substrate;
• a mesa structure which protrudes from the substrate and extends in an extending direction parallel to the substrate, and which includes an active layer;
• a first buried layer of a semiconductor and a second buried layer of the semiconductor, the first buried layer being placed on a first side of the mesa structure in a section perpendicular to the extending direction, the second buried layer being placed on a second side of the mesa structure in the section;
• and
• an electrode which is formed on the mesa structure and which is partially placed on the first buried layer and the second buried layer,
• wherein a top surface of the first buried layer has a first sloped portion which slopes in a width direction of the mesa structure so as to be closer to the substrate as a distance from the mesa structure increases,
• wherein a top surface of the second buried layer has a second sloped portion which slopes in the width direction so as to be closer to the substrate as a distance from the mesa structure increases,
• wherein the electrode covers an entirety of the first sloped portion and an entirety of the second sloped portion.