High carrier density CeO2 dielectrics—implications for MOS devices

Nanocrystalline CeO2 films of 75 nm thickness were deposited on n-type (100) silicon substrates using pulsed laser deposition (PLD) technique to form a gate dielectric in the Pt/Si/CeO2/Pt MOS capacitor. XRD and AFM were used for characterization of the film crystal structure and grain size. Electrical properties of the MOS structure were examined by capacitance–voltage (C–V) and impedance spectroscopy measurements. Based on the impedance measurements and reported electron mobilities, we derive a rather high carrier density of the order of 6×1017 cm−3. Nevertheless, their overall high resistance enables the films to serve as dielectrics. In contrast to conventional MOS capacitors, we find an additional capacitive contribution under accumulation we attribute to the electron depletion in the CeO2 film. We present a model consistent with these results.