A distributed feedback semiconductor diode laser includes a substrate of n-type gallium arsenide having a channel along one surface thereof. A first clad layer of n-type aluminum gallium arsenide is on the surface of the substrate. The first clad layer fills the channel and has a planar surface. An active layer of undoped aluminum gallium arsenide is on the first clad layer and a first spacer layer of p-type conductivity aluminum gallium arsenide is on the active layer. A grating layer of p- type conductivity aluminum gallium arsenide is on the first spacer layer and has a second order grating therein which extends across the channel in the substrate. A second spacer layer of p-type conductivity aluminum gallium arsenide is on the grating layer and a second clad layer of p- type conductivity aluminum gallium arsenide is on the second spacer layer. The content of aluminum in the second clad layer varies across its thickness from an amount less than that in the second spacer layer at its junction with the second spacer layer to an amount equal to that in the second spacer layer. A cap layer of n-type conductivity gallium arsenide is on the second clad layer and a p-type conductivity contact region extends through the cap layer to the second clad layer over the groove in the substrate. Conductive contacts are on the contact region and a second surface of the substrate. The composition and thicknesses of the active layer, spacer layers and grating layer are such as to provide the output beam of the diode laser with a relatively low divergence angle of about 27°.
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