Abstract: A semiconductor laser having: a group III-V semiconductor substrate; a group III-V semiconductor clad layer disposed on the substrate with a lattice mismatch of 0.5% or more; group III-V semiconductor light propagation layers disposed on the clad layer, including an active layer and light confining layers on both sides of the active layer, the light confining layers containing Al as the group III element; a group III-V semiconductor buffer layer disposed between the substrate and the clad layer, the buffer layer including a composition graded layer gradually changing the lattice constant, and having a cross hatched step on the surface thereof; and an intermediate layer of group III-V semiconductor disposed between the buffer layer and the clad layer, the intermediate layer containing phosphorous as the group V element. A semiconductor laser of 1 .mu.

Abstract: A semiconductor laser having: a group III-V semiconductor substrate; a group III-V semiconductor clad layer disposed on the substrate with a lattice mismatch of 0.5 % or more; group III-V semiconductor light propagation layers disposed on the clad layer, including an active layer and light confining layers on both sides of the active layer, the light confining layers containing Al as the group III element; a group III-V semiconductor buffer layer disposed between the substrate and the clad layer, the buffer layer including a composition graded layer gradually changing the lattice constant, and having a cross hatched step on the surface thereof; and an intermediate layer of group III-V semiconductor disposed between the buffer layer and the clad layer, the intermediate layer containing phosphorous as the group V element. A semiconductor laser of 1 .mu.

Abstract: A group III-V compound semiconductor laser of a 1 .mu.m band having an excellent conversion efficiency and a high characteristic temperature. The semiconductor laser can emit light in a 1.3 .mu.m band or a 1.55 .mu.m, and has a laser structure including an active layer For emitting light, guide layers sandwiching the active layer and having a band gap larger than the active layer, and clad layers embracing the guide layers and having a band gap larger than the guide layers. The lattice constants of the guide layers and clad layers are larger than a1 by 0.5% or more and smaller than a2 by 0.5% or more, where a1 represents the lattice constant of GaAs and a2 is the lattice constant of InP.