Semiconductor laser device

A semiconductor laser device comprising:

• a first semiconductor layer formed over a substrate and made of a first nitride semiconductor of a first conductivity type;
• a second semiconductor layer formed over the first semiconductor layer and made of a second nitride semiconductor, the energy gap of the second nitride semiconductor being smaller than that of the first nitride semiconductor;
• and
• a third semiconductor layer formed over the second semiconductor layer and made of a third nitride semiconductor of a second conductivity type, the energy gap of the third nitride semiconductor being larger than that of the second nitride semiconductor,
• wherein the first or third nitride semiconductor contains phosphorus,
• wherein the first and second conductivity types are n-type and p-type, respectively, and
• wherein the first and third nitride semiconductors have respective compositions AlGaN1—xPx and AlGaN1—yPy (where 0<x<y).