Open volume defects in ultra-thin TiO2 layers embedded in VMCO-like samples studied with positron annihilation spectroscopy

Positron annihilation signals from VMCO-like samples grown by atomic layer deposition at different temperatures are utilized for the characterization of differences in open volume defects in TiN/TiO2/a-Si heterostructures. Doppler and coincidence Doppler mode of positron annihilation spectroscopy combined with a monoenergetic positron beam were used for this study. Differences observed in the Doppler parameters indicate differences in the positron trapping states of the TiO2 epilayers grown at different temperatures. Furthermore, the coincidence-Doppler results show that these differences cannot be due to intermixing of the TiO2 and a-Si layers and formation of thin SiO2 layers at the interface during the growth process. The results indicate that the amount of open volume defects in the TiO2 layer of the VMCO-structure seems to increase with an increase in the growth temperature.