Positively Charged Defects in Ta2O5 and Nb2O5: Are They Correlated with Sodium Ions?

In the present study, capacitance-voltage and triangular voltage sweep (TVS) measurements reveal mobile positively charged defects in both Ta2O5 and Nb2O5 layers deposited on thin SiO2 layers. These defects are not detected in the SiO2 layers before the deposition of high-k oxides and their concentration depends significantly on the purity of the targets. The electrical properties of these defects are found to be similar to those of positively charged Na+ in SiO2. Vapor-phase decomposition-inductively coupled plasma-mass spectrometry (VPD-ICPMS) measurements show that Na is a dominant signal besides Ta and Nb after the deposition of Ta2O5 and Nb2O5, respectively. Considering these findings, the origin of the positively charged defects is discussed with an emphasis on their correlation with Na+.