Abstract: A semiconductor laser includes (a) a semiconductor substrate of a first conductivity type on which is provided (b) a mesa stripe portion having a multilayer structure. The multilayer structure includes (b-1) an active layer provided on the semiconductor substrate. The laser also includes (c) a buried current blocking layer arranged on both sides of the mesa stripe portion, (d) a clad layer of a second conductivity type provided on the semiconductor substrate through at least a portion of the active layer, and (e) a contact layer of the second conductivity type provided on the clad layer. The contact layer includes a first contact layer contacting the clad layer and a second contact layer provided on the first contact layer. The first contact layer has an energy gap smaller than that of the clad layer and larger than that of the second contact layer. Preferably, the first contact layer is an InGaAsP semiconductor layer having an energy gap within the range of from 0.82 eV to 1.

Abstract: A semiconductor laser having a multi-layer film which is inclusive of an active layer and formed on an InP substrate, in which at least one layer adjacent to the active layer is formed of a material which is a composition having a larger band gap than InP and whose component ratio is so selected as to match with the lattice constant of InP, thereby to ensure that minority carriers injected into the active layer efficiently contribute to laser operation. The material has a composition including at least three elements in addition to InP.

Abstract: A semiconductor laser formed on an InP substrate to have a hetero structure comprising a plurality of In.sub.1-x Ga.sub.x`As.sub.y P.sub.1-y (0.42y.ltoreq.x.ltoreq.0.5y,0.ltoreq.y.ltoreq.1) layers which are lattice-matched with InP, in which a light emitting layer included in the layers and having a forbidden band width larger than 0.6 eV but smaller than 0.9 eV at room temperature is sandwiched between two InP layers on the InP substrate, and in which there is provided between the light emitting layer and the InP layer grown thereon at least one buffer layer having a forbidden band width larger than the forbidden band width of the light emitting layer but smaller than the forbidden band width of InP. The forbidden band width of the buffer layer at room temperature may be larger than 0.8 eV but smaller than 1.0 eV.