Role of Ti phases in the modulation of border traps at the TiO2/n-Si interfaces

Charge accumulation at interfaces is a key issue for the use of high dielectric constant materials in nanoelectronics. In this work, we report the charge accumulation behavior at the TiO2/n-Si interfaces formed at various growth temperatures. Growth of TiO2 in an oxygen deficient environment led to the formation of rutile phase in the as-grown films. The anatase phase was recovered by annealing in air and the ratio of anatase to rutile phase in the TiO2 films improved considerably. The amount of charge accumulation and the direction of charge injection were studied by obtaining C-V hysteresis curves in the as-grown and the annealed TiO2 films. It was observed that the amount of accumulated charges decreased as the density of interface border traps dropped considerably due to annealing. X-ray photo-electron spectroscopy revealed the presence of two major phases corresponding to TiO2 and Ti2O3, due to the existence of oxygen deficiencies. The annealing in air resulted in appreciable increase in the weight percentage of TiO2 phase in samples grown at high temperatures. The healing of oxygen vacancies improved with the increase in the weight percentage of TiO2. Thus, it was concluded that the accumulated charges were mainly due to oxygen deficiencies and the healing of oxygen defects led to a drop in the interface charges, thus, bringing the interface close to ideal.