In a semiconductor laser device having a quantum well active layer, an
undoped thin spacer layer is formed between an undoped optical guide layer
and a p-type cladding layer. The thickness of the spacer layer is
preferably 5 nm or more but less than 10 nm. The spacer layer absorbs
impurities diffusing thereinto from the p-type cladding layer. Thus, the
dopant is prevented from being diffused into the undoped optical guide
layer.
