Defects in Si-dopedInxAl1−xAs(0<x<0.4)epilayers on GaAs substrates were systematically investigated by deep-level transient spectroscopy. Three electron traps, ranging from 0.22 to 0.89 eV, were observed inInxAl1−xAsgrown by molecular beam epitaxy. Their energy levels can be extrapolated from those in theInxAl1−xAs/InPsystem. A low-temperature-grown buffer layer as well as thermal annealing were found to be capable of reducing the defects in the active layer effectively. ©1997 American Institute of Physics.