Grain size and thickness effect on the performance of sol–gel based TiO2 Schottky diodes

This paper reports thickness and grain size effect on the Schottky diodes of Titanium oxide (TiO2) films made by a sol–gel process. The TiO2 sol was prepared using titanium isopropoxide, ethanol and HCl. Fourier transform infrared spectra indicates that the single bondOH and free water molecule absorption intensities diminish as the heating time increases, whereas Tisingle bondOsingle bondTi and isolated Tisingle bondOH absorption peaks slowly increase as the heating time increases. When annealing temperature effect on the phase of TiO2 was investigated, no phase transformation from anatase to rutile was observed until the annealing temperature of 750 °C, and only small portion of the phase transformation occurred after annealing at 850 °C. Schottky diodes comprised of p-Si/TiO2/Al were fabricated with various thicknesses of TiO2 film made by different number of TiO2 coatings. In the I–V characteristics, the forward current of Schottky diodes increases as the TiO2 film thickness increases. To understand the cause of the forward current enhancement, three different conduction mechanisms are investigated, and there was no conduction mechanism change with the thickness increase. The enhancement of the forward current was possibly due to the grain size effect.