Admittance spectroscopy and deep-level transient spectroscopy measurements have been performed onn+-on-pHg1−xCdxTe(x=0.595)planar photodiodes grown by improved zone melt method. After 1.0 Mrads gamma irradiation, a new trap center is observed at 0.19 eV above the valence band, while the well-known 0.15 eV trap level disappears. The trap densities for these two levels are almost the same. We attribute this phenomenon to the gamma irradiation, which produces a compound defect correlated with Hg vacancy. ©1998 American Institute of Physics.