A semiconductor laser diode and method are described, wherein the path of the
current
through the device between the positive and negative conductors is controlled.
Lateral spread of the gain current in the active region is prevented by implanting
protons in areas of the active layer flanking a desired gain region. The implanted
regions become less conductive, and prevent lateral spread of the gain current.
The position of the implanted regions can be selected so that the gain current
only crosses a portion of the active layer that supports desired lateral modes
of the laser light.