Optical semiconductor element, optical semiconductor device, optical transmission system, and method of manufacturing optical semiconductor device

An optical semiconductor element comprising:

• a semiconductor substrate that is semi-insulating;
• a columnar body that is formed on a front surface-side of the semiconductor substrate and configured to emit or receive light from the front surface-side;
• a front surface-side electrode that is connected to the columnar body;
• a back surface-side electrode formed on a back surface-side of the semiconductor substrate;
• and
• an electrically conductive member that is formed to penetrate through the semiconductor substrate to connect the front surface-side electrode and the back surface-side electrode, and has a protruding portion protruding, with respect to the front surface-side electrode, on the front surface-side of the semiconductor substrate,
• wherein the electrically conductive member is arranged separately from the columnar body,
• wherein the protruding portion has a height exceeding an upper surface of the columnar body, and
• wherein a top surface of the protruding portion is positioned higher than the upper surface of the columnar body and is separated from the upper surface of the columnar body.