Kinetic Monte Carlo Simulations of Defects in Anatase Titanium Dioxide

Anatase titanium dioxide is a highly promising material for memristors and photocatalysis. Multiple electronic transport processes are known to be influenced by defects in nanoscale anatase. Hence, in this study, we examine charge transport due to defects with respect to the fabrication of nanometer-thin TiO2 films via kinetic Monte Carlo (kMC). A compact kMC model for metal oxide semiconductor (MOS) and metal oxide metal (MOM) structures comprising TiO2 was parametrized by the electronic properties of TiO2 in agreement with the literature, in particular, spectroscopic studies and DFT calculations on defects in anatase. kMC simulations of MOS structures were refined, for the first time, by separate drift-diffusion simulations on the band bending in p(+)-Si substrates as well as by barrier heights adjusted for the Fermi level pinning effect. Referring to the impact of specific TiO2 film growth methods and postgrowth treatments on the parameters for defect energies in particular, electrical jV characteristics of material stacks fabricated by PVD and CVD methods, as reported in the literature, were reproduced computationally at high accuracy. Thus, conclusions on the dependence of electron trap levels in anatase on the sample processing could be drawn from this kMC-based computational analysis, attributing defects in TiO2 to shallow titanium interstitials (Ti-int) or deep oxygen vacancies (V-o), depending on the fabrication methods.