Al/In x Ga 1−x As (001) diodes incorporating Si bilayers deposited under As or Al flux were fabricated by molecular-beam epitaxy on GaAs(001) wafers for 0.2<x<0.4. Schottky barrier heights as high as 0.75 eV and as low as −0.10 eV could be reproducibly obtained. Diodes engineered for high barrier height systematically showed a higher thermal stability than low-barrier diodes. We discuss the composition dependence of the barrier height and the observed degradation behavior vis-a-vis of the predictions of the interface-dipole model of Schottky barrier tuning.