Metastable defects generated by hole injections under constant current condition are studied above room temperature. The defect saturation behavior is observed after a sufficient period of current soaking, while it is faster at higher temperatures. The saturated defect density is obtained from the space charge limited current. A simple model is proposed for the defect kinetics, which considers hole induced defect creation and annihilation as well as the thermal annealing processes. This model includes a dispersive hydrogen diffusion and is found to be well fitted into present experimental data.
The effective barrier hight $E_τ$ and the width of the barrier distribution $T_0$ in the defect creation process is obtained from the measured temperature dependence of current density. The values for $E_τ$ and $T_0$ are found to be 1.21eV and 650K, respectively. We find that $E_τ$ is lowered as the electric field is increased, whereas $T_0$ is nearly unchanged. This result are discussed using the carrier-enhanced hydrogen diffusion process. Injected carriers are found to reduce the hydrogen diffusion barrier which affects $E_τ$.
Different annealing behaviors are found for positively charged defects($D^+$) and neutral defects($D^0$). It is found to be more difficult to anneal $D^+$ than $D^0$. This behavior is attributed to the fact that the annealing of $D^+$ needs an extra energy to promote an electron from the valence band to the defect energy level.