Semiconductor laser

An article comprising a unipolar semiconductor laser, said laser comprising

• a) a multilayer semiconductor structure that comprises doped semiconductor material of only a first conductivity type;
• and
• b) means for applying a voltage across said multilayer semiconductor structure;
• CHARACTERIZED IN THAT
• c) said multilayer structure comprises a multiplicity of essentially identical active regions, a given of said active regions being separated from an adjoining active region by a superlattice carrier injection/relaxation region;
• d) the given active region comprises a single quantum well, associated with said quantum well are a first and a second energy state for charge carriers of the first conductivity type, with said second energy state being higher in energy than said first energy state;
• e) said superlattice carrier injection/relaxation region is selected to be relatively transmissive for carriers in the first energy state, and to be substantially less transmissive for carriers in the second energy state;
• and
• f) at least some of the charge carriers of the first conductivity type undergo a radiative transition from the second to the first energy state.