Optical and transport properties of nonstoichiometric tantalum oxide thin films grown by ion beam deposition were investigated in order to understand the dominant charge transport mechanisms and reveal the nature of traps. The TaO films composition was analyzed by X-ray photoelectron spectroscopy and by quantum-chemistry simulation. From the optical absorption and photoluminescence measurements and density functional theory simulations, it was concluded that the 2.75 eV blue luminescence excited in a TaO by 4.45 eV photons, originates from oxygen vacancies. These vacancies are also responsible for TaO conductivity. The thermal trap energy of 0.85 eV determined from the transport experiments coincides with the half of the Stokes shift of the blue luminescence band. It is argued that the dominant charge transport mechanism in TaO films is phonon-assisted tunneling between the traps.
The p-Si(or n-Si)/GeO[SiO2] (or GeO[SiO])/indium-tin-oxide (ITO) structures were fabricated by simultaneous evaporation of GeO2 and SiO2 (or SiO) powders in high vacuum and further deposition of ITO contacts using the magnetron sputtering technique. The structural properties of the GeO[SiO2] and GeO[SiO] films were studied using FTIR and Raman spectroscopy. According to Raman data, the GeO[SiO] films deposited at a temperature of 100 °C contain amorphous Ge clusters. Their current-voltage characteristics were measured in the air atmosphere, and resistive switching (memristor effect) was observed in structures without a preliminary forming procedure. The Shklovskii-Efros percolation model gives a consistent explanation for the charge transport in the high-resistive state and the low-resistive state of memristors based on GeO[SiO2] or GeO[SiO] films.
Lanthanum-doped HfZrO is considered as the ferroelectric material for capacitor structures used in one-transistor-one capacitor nonvolatile memory cells for the development of new generation nonvolatile random-access memory. Here, different capacitor structures are characterized by x-ray photoelectron spectroscopy electrically to determine the electron and hole contribution to the conductivity in these capacitor structures. Experiments related to the minority carrier's injection and charge transport from an n-Si and a p-Si substrate into a lanthanum-doped HfZrO layer show that the conductivity is bipolar. Electrons are injected into La:HfZrO from a negatively biased contact, and accordingly, holes are injected from a positive voltage biased electrode.
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