Semiconductor device having improved electronic isolation

A semiconductor device, comprising:

• a substrate of GaAs;
• an active layer of a compound semiconductor material provided on said substrate, said active layer including therein an active device;
• a buffer layer of AlGaAs provided between said substrate and said active layer, said buffer layer containing oxygen in a concentration within the approximate range of 8.times.10.sup.17 cm.sup.-3 to 6.times.10.sup.19 cm.sup.-3 and carbon in a concentration within the approximate range of 2.times.10.sup.16 cm.sup.-3 to 2.times.10.sup.17 cm.sup.-3 ;
• said buffer layer of AlGaAs having a lattice constant that is smaller than a lattice constant of an undoped AlGaAs crystal identical in composition with said buffer layer but undoped with oxygen;
• wherein said lattice constant of said AlGaAs buffer layer is larger than a lattice constant of said GaAs substrate such that a lattice misfit of said AlGaAs buffer layer with respect to said GaAs substrate is equal to or varies by no more than 2.times.10.sup.-5 from a corresponding lattice misfit between said undoped AlGaAs crystal with respect to said GaAs substrate.