Electronic conductivity and dielectric properties of nanocrystalline CeO2 films

The growth of dielectric layers on silicon substrates has attracted a great deal of recent interest given their potential applicability in the fabrication of high quality silicon-on-insulator (SOI) structures, high density capacitor devices, and stable buffer layers between silicon and other materials. In this study, nanocrystalline CeO2 films were deposited on n-type (100) silicon substrates using pulsed laser deposition (PLD) to form a gate dielectric for a Pt/n-Si/CeO2/Pt MOS device. XRD, AFM and FESEM measurements were used to characterize the crystal structure and grain size of the CeO2 films. The electrical properties of the device structure were examined by capacitance-voltage (C-V) and impedance spectroscopy measurements. The CeO2 films exhibited an activated conductivity, characterized by an activation energy E-a = 0.45 eV. An estimated room temperature electron mobility mu(e) of 2.8 x 10(-7) cm(2)/Vs leads to a corresponding electron concentration n of 5.5 x 10(17) cm(-3). In contrast to conventional MOS capacitors, we find an additional capacitive contribution under strong accumulation conditions as a result of space charge effects inside the CeO2 thin film.