Dielectric functions of solution-processed GdAlOx/Si films measured with vacuum ultra-violet spectroscopic ellipsometry

The dielectric functions of amorphous GdAlOx (GAO) films grown by the sol-gel process were investigated from 1.12 to 8.5 eV as a function of annealing temperature using spectroscopic ellipsometry (SE). A GAO precursor sol with a molar ratio of Gd:Al=1:1 was prepared. Thin layers were formed by spin-coating on p-type Si substrates. The layers were sintered at 400 °C for 2 h in an ambient atmosphere, then rapid-thermal-annealed (RTA) at 700 or 800 °C for 1 min in an N₂ ambient. The optical properties were measured via variable angle SE, at room temperature. The angle of incidence was varied from 50 to 70° in 10° steps. The dielectric functions of the resulting GAO films were obtained from the measured pseudodielectric functions by multilayer-structure calculations using the Tauc-Lorentz (TL) dispersion relation. The real and imaginary parts of the dielectric functions were found to increase with increasing RTA temperature. The film thicknesses and TL parameters (threshold energy E_g and broadening C) decrease with increasing RTA temperature.