Comparative investigation of interfacial characteristics between HfO₂/Al₂O₃ and Al₂O₃/HfO₂ dielectrics on AlN/p-Ge structure

The electrical and interfacial properties of HfO₂/Al₂O₃ and Al₂O₃/HfO₂ dielectrics on AlN/p-Ge interface prepared by thermal atomic layer deposition are investigated by capacitance-voltage(C-V) and current-voltage(I-V) measurements. In the C-V measurements, humps related to mid-gap states are observed when the ac frequency is below 100 kHz, revealing lower mid-gap states for the HfO₂/Al₂O₃ sample. Higher frequency dispersion in the inversion region is observed for the Al₂O₃/HfO₂ sample, indicating the presence of slow interface states A higher interface trap density calculated from the high-low frequency method is observed for the Al₂O₃/HfO₂ sample. The parallel conductance method, applied to the accumulation region, shows border traps at 0.3~0.32 eV for the Al₂O₃/HfO₂ sample, which are not observed for the Al₂O₃/HfO₂ sample. I-V measurements show a reduction of leakage current of about three orders of magnitude for the HfO₂/Al₂O₃ sample. Using the Fowler-Nordheim emission, the barrier height is calculated and found to be about 1.08 eV for the HfO₂/Al₂O₃ sample. Based on these results, it is suggested that HfO₂/Al₂O₃ is a better dielectric stack than Al₂O₃/HfO₂ on AlN/p-Ge interface.