XPS analysis and electrical conduction mechanisms of atomic layer deposition grown Ta2O5 thin films onto p-Si substrates

Abstract

Metal oxide semiconductor capacitors that incorporate tantalum pentoxide (Ta2O5) thin films as dielectric were fabricated via the atomic layer deposition (ALD) technique and characterized through TEM, XPS, C–V, and I–V measurements. TEM analysis revealed the amorphous phase of Ta2O5 films and the existence of an ultrathin SiOx layer in the Ta2O5/p-Si interface, also evidenced by XPS spectra. XPS analysis verified the stoichiometry of the ALD-deposited Ta2O5 films. Furthermore, XPS results indicate values of 2.5 and 0.7 eV for the conduction and valence band offsets of the Ta2O5/p-Si interface, respectively. I–V measurements, for positive and negative applied bias voltages, reveal that the conduction is governed by Ohmic, trap controlled space charge limited, and Schottky mechanisms depending on the applied voltage and temperature region. Through the analysis of Schottky emission data, the conduction band offset of Ta2O5/p-Si (φΒ) is calculated to be 0.6 eV, while the valence band offset is 2.6 eV, in very good agreement with the XPS results. The energy band diagram of Ta2O5/p-Si is constructed.