Si‐implant activation characteristics in AlxGa1−xAs for Al compositions of 0%–70% AlAs are presented for doses of 5.6×1012and 2.8×1013cm−2at 100 keV. For both doses, the effective activation efficiency (&eegr;eff) is relatively constant from 0% to 20% AlAs (&eegr;eff=64% for 5.6×1012cm−2and 37% for 2.8×1013cm−2for 20% AlAs), goes through a minimum at 35% AlAs (&eegr;eff=6.6% for 5.6×1012cm−2and 2.5% for 2.8×1013cm−2), and then increases towards 70% AlAs (&eegr;eff=52.8% for 5.6×1012cm−2and 31.1% for 2.8×1013cm−2). The results are explained based on the compositional dependence of the ionization energy and conduction band density‐of‐states of AlGaAs. The effects of P coimplantation is also studied but demonstrates no significant enhancement of the activation efficiency of Si implantation for 0%–70% AlAs. Finally, data are presented for Se implantation in Al0.2Ga0.8As with a maximum effective activation efficiency of 5.6% achieved. ©1996 American Institute of Physics.