Exploring point defects and trap states in undoped SrTiO3 single crystals

The defect chemistry and electronic trapping energies in undoped single crystalline SrTiO3 were examined by electrochemical impedance spectroscopy at low (25-160 degrees C) and intermediate (500-700 degrees C) temperatures. Electronic and ionic conductivity as well as chemical capacitance values were obtained with a transmission line equivalent circuit. Impedance spectroscopy at low temperatures was used to quantify trapping energies of main ionic defects. Particularly the chemical capacitance is shown to be a highly valuable, though hardly used tool for establishing a defect model based solely on electrochemical measurements. It is very sensitive for minority charge carriers and can thus unveil otherwise hardly accessible defect concentrations. The chemical capacitance analysis yields a valence dependent acceptor concentration in the ppm range for the investigated samples. Complementary positron annihilation lifetime spectroscopy (PALS) suggests existence of Ti vacancies and both methods (chemical capacitance and PALS) agree in their quantification of the corresponding vacancy concen-tration (6 ppm). Beyond successfully predicting acceptor defect concentrations in undoped SrTiO3, the method is sensitive for electronically relevant defects in sub-ppm concentrations.

Automated summary

The defect chemistry and electronic trapping energies in undoped single crystalline SrTiO3 were investigated using electrochemical impedance spectroscopy and positron annihilation lifetime spectroscopy. The results showed that the chemical capacitance is a valuable tool for establishing a defect model based on electrochemical measurements and analyzing defect concentrations. The chemical capacitance analysis and positron annihilation lifetime spectroscopy are consistent in quantifying the defect concentrations in SrTiO3.