The work reported here was performed in order to establish whether or not complex defects like the D-X center can be present in InAlAs. Dominant deep electron and hole traps in lattice-matched In 0.52 Al 0.48 As/InP have been identified and characterized. The traps have activation energies ranging from 0.25 to 0.95 eV. The electron traps have very large capture cross-sections,~10 -12 -10 -11 cm 2 , similar to attractive centers. The lattice-matched samples do not show any persistent photoconductivity effects at low temperatures. In strained In 1-x Al x As with 0.48 <x ≤ 0.57, an electron trap with a thermal ionization energy of 0.35 eV, a strong dependence of its concentration on donor doping and very small thermal capture cross-section, 10 18 cm 2 , is identified. These samples exhibit persistent photoconductivity. We believe this trap is similar to the D-X center commonly observed in Al x Ga 1-x As for x ≥ 0.28.