Electronic and optical properties of Al₂O₃/SiO₂ thin films grown on Si substrate

The electronic and optical properties of Al 2 O 3 /SiO 2 dielectric thin films grown on Si(1 0 0) by the atomic layer deposition method were studied by means of x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy (REELS). The band gaps of the Al 2 O 3 /SiO 2 thin films before annealing and after annealing were 6.5 eV and 7.5 eV, respectively, and those of the γ-Al 2 O 3 and α-Al 2 O 3 phases were 7.1 eV and 8.4 eV, respectively. All of these were estimated from the onset values of the REELS spectra. The dielectric functions were determined by comparing the effective cross-section determined from experimental REELS with a rigorous model calculation based on dielectric response theory, using available software packages. The determined energy loss function obtained from the Al 2 O 3 /SiO 2 thin films before annealing showed a broad peak at 22.7 eV, which moved to the γ-Al 2 O 3 position at 24.3 eV after annealing. The optical properties were determined from the dielectric function. The optical properties of the Al 2 O 3 /SiO 2 thin films after annealing were in good agreement with those of γ-Al 2 O 3 . The changes in band gap, electronic and optical properties of the Al 2 O 3 /SiO 2 thin films after annealing indicated a phase transition from an amorphous phase to the γ-Al 2 O 3 phase after annealing.