We describe the electrical properties of atomic layer deposited TiO2/Al2O3 bilayer gate oxides which simultaneously achieve high gate capacitance density and low gate leakage current density. Crystallization of the initially amorphous TiO2 film contributes to a significant accumulation capacitance increase (∼33%) observed after a forming gas anneal at 400 °C. The bilayer dielectrics reduce gate leakage current density by approximately one order of magnitude at flatband compared to Al2O3 single layer of comparable capacitance equivalent thickness. The conduction band offset of TiO2 relative to InGaAs is 0.6 eV, contributing to the ability of the stacked dielectric to suppress gate leakage conduction.
Band offsets of the Al2O3/GaSb system and various surface passivation treatments of the GaSb substrate by HCl, NH4OH, and (NH4)2S solutions were investigated by x-ray photoelectron spectroscopy. The extracted conduction and valence band offsets values of Al2O3 relative to GaSb are 2.4±0.1 eV and 3.4±0.2 eV, respectively. The presence of Ga–O and Sb–O bonds was detected after NH4OH surface treatment. In contrast, (NH4)2S and HCl solutions inhibit the Sb oxide formation. The lowest amount of Ga–O bands was obtained for (NH4)2S passivation. These results correlate with capacitance-voltage (C-V) measurements of Pd–Au/Al2O3/GaSb stacks which yielded the best characteristics for the S-based passivation.
The energy band gap, alignment with Si and the chemical bonding of 3-4 nm thick Hf x Si 1−x O 2 films with 0 Յ x Յ 1 were investigated as a function of composition. Nitrogen was introduced by N plasma incorporation into Hf x Si 1−x O 2 films with x = 0.3, 0.5, and 0.7 grown on a SiO 2 / Si stack by metal-organic chemical vapor deposition. The structure of the dielectric films was characterized by high resolution transmission electron microscopy. X-ray photoelectron spectroscopy was used to determine the band gap, as well as the energy band alignment with Si and the chemical structure of the films. The amount of Si in the films and the incorporated N were found to influence the band gap and the band alignment with Si. The band gap was found to gradually decrease with the increase in Hf content, from a value of 8.9 eV ͑for pure SiO 2 ͒ to a value of 5.3 eV ͑for pure HfO 2 ͒. These changes were accompanied by a reduction of the valance band offset relative to the Si substrate, from a value of 4.8 eV ͑for pure SiO 2 ͒ to a value of 1.5 eV ͑for pure HfO 2 ͒. In addition, we have found that the presence of Hf-N bonds increases the conduction band offset from a value of 2.7 eV, which was obtained when only Hf-O bonds are present, to a value of 3.1 eV. The changes in the band structure and band alignment of Hf-silicate films are explained based on the chemical structure of the nitrided Hf-silicate films.
The energy band gap, the band alignment with Si, and the chemical bonding of 4–5 nm thick (TbxSc1−x)2O3 dielectric films were investigated as a function of composition. Films with x=0, 0.5, and 1 were prepared by a molecular beam deposition technique on silicon substrates. The structure of the dielectric films was characterized by high resolution transmission electron microscopy. We found that upon deposition, a silicate and a silicon oxide layer were formed at the dielectric/silicon interface for all compositions. X-ray photoelectron spectroscopy was used to determine the band gap, as well as the energy band alignment with Si and the chemical structure of the films. Energy gap values of 6.0±0.2 and 7.5±0.2 eV were obtained for pure Sc2O3 and Tb2O3, respectively, while for the mixed layer (x=0.5) a value of 6.8±0.2 eV was extracted. It was found that the valence band offset does not change with Sc addition to Tb2O3, while the conduction band offset increases with x, from a value of 2.9±0.2 eV for the x=0 (pure Sc2O3) to a value of 5.7±0.2 eV for x=1 (pure Tb2O3).
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