Sodium impurities in amorphous and crystalline Ta2O5

Through capacitance-voltage and triangular voltage sweep (TVS) measurements, mobile positively charged ions were observed in structures with as-deposited amorphous Ta2O5 and crystalline β-Ta2O5 layers obtained after subsequent annealing of amorphous layers at 950 °C in O2 and Ar atmospheres. Analysing the shift of the characteristic TVS peak corresponding to these defects at different temperatures, we determined the activation energy for ion drift to be 360 meV and 380 meV in amorphous and crystalline Ta2O5 layers, respectively. Ion-coupled mass spectrometry (ICP-MS) measurements revealed that Na was the predominant defect in the as-deposited Ta2O5, with its intensity significantly surpassing that of other defects. Consequently, we attribute the positively charged defects to interstitial Na+ ions, which are likely to be incorporated into the targets used for deposition.