Electrical conduction mechanisms and dielectric relaxation in Al2O3 thin films deposited by thermal atomic layer deposition

In the present work, aluminum oxide (Al2O3) thin films were deposited on p-type silicon substrates by thermal atomic layer deposition technique. The structural properties of as-deposited Al2O3 thin films were characterized by grazing-incidence x-ray diffraction and it was determined that the films had an amorphous structure. Electrical transport mechanisms and dielectrical properties of the amorphous Al2O3 thin films were then investigated by fabricating and characterizing Al/Al2O3/p-Si metal-oxide-semiconductor (MOS) capacitors by performing the dc current-voltage and frequency-dependent dielectric measurements. As a function of the applied gate electric fields, the current conduction in low electric fields consists of Schottky emission, but in relatively high electric fields current conduction is dominated by space-charge limited conduction. From the frequency-dependent dielectric measurements, the dielectric loss showed two peaks at the frequencies of 10 kHz and 0.7 MHz which evidence of the dielectric relaxation. The low and high frequency dielectric relaxation behaviors were attributed to space charge polarization and orientation-polarization of dipoles, respectively. It was concluded that defects related localized states in the Al2O3 films may contribute to dielectric properties at high frequency.