hafnium oxide layer with oxygen vacancies

Hence we chose tetragonal HfO2 for this study. Oxygen vacancies are the dominant intrinsic defects in the bulk of many transition metal oxides including HfO2 and thought to be also present in high concentration in thin films. Therefore, accurate characterization of the leakage current caused by oxygen vacancies in MOS structures is highly desirable.. The supercell method was used to study comparatively the defect energetics in monoclinic hafnium oxide and α-quartz. As a comparison, the tunneling current through the perfect oxide is also given in this figure. Checking this figure in detail, one can see that the tunneling currents possess the typical characteristic of stress-induced leakage current. This figure clearly illustrates that such oxygen vacancies in HfO2 high-K gate dielectrics of a MOS structure can be an origin of the stress-induced leakage current. On the basis of the first-principles simulations of the defect t-HfO2 layer using the supercell method, the effect of the oxygen vacancies on the electronic structure has been studied. A defect band at Ec – 1.25 eV caused by oxygen vacancies within the bandgap is obtained, which agrees well with the value in Ref. [13]. By analyzing the band structure and the density of states of the t-HfO2 supercell with one oxygen vacancy, the unbonded Hf d orbitals in the t-HfO2 supercell are found to give the largest contribution to the defect band within the bandgap of t-HfO2. Combining with the defect level obtained from first principles simulations, tunneling currents through an ultrathin hafnium oxide layer with oxygen vacancies are calculated via a two-step tunneling process. Numerical calculations of tunneling currents through ultrathin hafnium oxide layer with oxygen vacancies show that oxygen vacancies could result in an increase in the tunneling current due to the defect band introduced into the bandgap of hafnium oxide. The calculated tunneling currents including defect assisted tunneling possess the typical characteristic of the stress-induced leakage current. The calculations also show that the largest increase in the gate leakage current will occur at a medium oxide electric field when the defects locate at the middle of the oxide. Wherever oxygen vacancies locate in the t-HfO2 layer it always results in an increase in the tunneling current at a low field. In summary, all calculations demonstrate that such oxygen vacancies can be an origin of the stress-induced leakage current in MOS structures with HfO2 high-K gate dielectrics.

PSS Journal, First-principles simulations of the leakage current in metal–oxide–semiconductor structures caused by oxygen vacancies in HfO2 high-K gate dielectric