The effects of biased irradiation on Ge MOS capacitors with HfxZr1–xOy (0.43 < x < 1) gate dielectrics have been investigated. These devices were irradiated by a 662-KeV Cs $^{137} \gamma $ -ray radiation source with 0.5 or –0.5 V gate bias. Prior to irradiation exposure, leakage behavior and bias-instability of HfxZr1–xOy films were also examined. Gate leakage current density increases with the increasing of Zr composition in gate oxide. In addition, Zr-containing dielectrics under positive bias (PB) exhibited more oxide negative trapped charges than that of HfO2, which suggested that the oxygen-vacancy concentration in HfxZr1–xOy was increased by the addition of Zr. Larger flat-band voltage shifts ( $\Delta V_{\mathrm {FB}})$ were extracted under positive biased irradiation than the bias only results. The results indicate that radiation-induced interface traps ( $\Delta N_{\mathrm {it}})$ are the dominant factor for $\Delta V_{\mathrm {FB}}$ in HfO2 thin films, whereas the radiation response for Zr-containing dielectrics under PB was mainly due to oxide traps. Under negative biased irradiation, $\Delta V_{\mathrm {FB}}$ was attributed to the combined effect of the net oxide trapped charges and the passivation of Ge dangling bonds at the Ge/high-k interface. Additionally, both bias-induced and radiation-induced charge trapping have a crucial effect on radiation response of HfxZr1–xOy at each dose level. HfxZr1–xOy is identified as a promising gate dielectric for advanced complementary metal–oxide–semiconductor technologies.