Mode-locked semiconductor laser device and driving method thereof

A method of driving a mode-locked semiconductor laser device comprising:

• (a) a laminated structure in which a first compound semiconductor layer having a first conductive type and composed of a GaN base compound semiconductor, a third compound semiconductor layer having an emission region composed of the GaN base compound semiconductor, and a second compound semiconductor layer having a second conductive that is different from the first conductive type and composed of the GaN base compound semiconductor are successively laminated;
• (b) a second electrode formed on the second compound semiconductor layer;
• and
• (c) a first electrode electrically connected to the first compound semiconductor layer,
• wherein the laminated structure is formed on a compound semiconductor substrate having polarity,
• the third compound semiconductor layer includes a quantum well structure having a well layer and a barrier layer,
• the well layer has a depth of 1 nm or more and 10 nm or less,
• the barrier layer has an impurity doping density of 2×1018 cm−3 or more and 1×1020 cm−3 or less, and
• generating an optical pulse in the emission region by passing a current from the second electrode to the first electrode via the laminated structure.