Abstract: A semiconductor laser diode of a double hetero structure including a semiconductor substrate, a buffer layer, a clad layer of a first conductivity type, an active layer and a clad layer of a second conductivity type, all layers being sequentially formed over the substrate, characterized by an intermediate layer interposed at at least one of a region between the substrate and the first clad layer and a region between the second clad layer and the cap layer, the intermediate layer being adapted to reduce a series resistance component and thus make a flow of current smooth.

Abstract: A semiconductor laser including a semiconductor substrate, a back reflection layer formed over the semiconductor substrate, a first clad layer formed over the back reflection layer, an active layer formed over the first clad layer, the active layer having a width smaller than that of the first clad layer, and a second clad layer formed over the active layer. The second clad layer has a flat upper surface and a width identical to that of the first clad layer. A front reflection layer is formed over the second clad layer. The semiconductor laser also includes impurity diffusion regions of a first conductivity type and a second conductivity type. The impurity diffusion regions extend from the upper surface of the second clad layer to predetermined depth portions of the first clad layer and are in contact with opposite side portions of the active region, respectively. First and second electrodes adapted to oscillate laser beams are formed over the first and second conductivity type impurity diffusion regions.