Stripe‐geometry AlGaAs‐GaAs single quantum‐well heterostructure lasers are demonstrated in which the region complementary to the stripe (outside of and defining the stripe) is shifted to higher band gap, and lower refractive index, by low‐temperature (600 °C) Zn diffusion. Impurity‐induced Al‐Ga interdiffusion causes the single GaAs quantum well (x=0,Lz≊80 A˚) outside of the stripe region to be mixed (‘‘absorbed,’’x→x′) into the Alx′Ga1−x′As (x′∼0.3,Lz′≊0.18 &mgr;m) bulk‐layer waveguide of the crystal.