Temperature and frequency dependent dielectric properties of dysprosium oxide grown on Si(p) substrates

Abstract

Samples of Dy oxide thin films were prepared on quartz and Si(p) substrates for structural, optical and electrical investigations. These samples were annealed at different conditions and characterised by UV–vis absorption spectroscopy, X-ray fluorescence (XRF) and X-ray diffraction (XRD). The XRD shows that the prepared Dy oxide has a cubic structure. The ac electrical measurements were done on samples prepared in a metal/oxide/Si MOS configuration. The ac-conductance and capacitance were studied, as a function of frequency, gate voltage, and temperature in the range 293–400 K. The fixed and interface charge densities were determined. It was concluded that the adsorbed structural hydroxyl (OH) groups strongly reduce the relative permittivity and this hydroxyl can be removed from the bulk of the film by annealing at 500 °C in vacuum of about 10 −2 Pa. It was found that the “correlated barrier hopping” (CBH) model controls the frequency dependence of the conductivity at high frequencies, while the Kramers–Kronig (KK) relations explain the high-frequency dependence of the capacitance. The parameters of the CBH model were determined showing that the ac-conduction in crystalline Dy oxide is realised by bipolaron mechanism, where the barrier height of hopping is equal to the bandgap determined from the UV–vis absorption spectroscopy. The temperature dependence of the ac-conductivity shows a semiconducting behaviour, and the thermal activation energies were determined.