Photoemission study of SiO x (0≤x≤2) alloys
TL;DR: A three-peak structure of mainly O 2p--derived states is observed over the whole concentration range and is characteristic of the local bonding environment of oxygen in the form of a Si-O-Si bridge bond.
Abstract: Photoemission measurements of the core and valence levels and of the plasmon energies of ${\mathrm{SiO}}_{\mathrm{x}}$ (0\ensuremath{\le}x\ensuremath{\le}2) are presented. The samples were prepared in situ as thin films by sputter deposition of Si in an Ar-${\mathrm{O}}_{2}$ mixture. The Si 2p core-level spectra are analyzed in terms of five chemically shifted components corresponding to the basic Si bonding units Si-(${\mathrm{Si}}_{4\mathrm{\ensuremath{-}}\mathrm{n}}$${\mathrm{O}}_{\mathrm{n}}$), with n=0,1,...,4. The concentration of these bonding units as a function of oxygen concentration is essentially in agreement with the random-bonding model. However, some separation into oxygen- and silicon-rich phases is also evident at intermediate stoichiometries. Plasmon energies increase from 17 eV (x=0) monotonously to 20.8 eV (x=2). The energies are analyzed in terms of the film density. Partial densities of oxygen- and silicon-derived valence states were obtained by using x-ray and uv excitation. A three-peak structure of mainly O 2p--derived states is observed over the whole concentration range. It is characteristic of the local bonding environment of oxygen in the form of a Si-O-Si bridge bond. The valence-band width and, in particular, the valence-band maximum (VBM) depend on the connectivity of the network structure. An abrupt shift of the VBM by 3.5 eV to greater binding energies at ${x}_{c}$=1.5 marks the disappearance of the Si-Si bonding states which define the valence-band maximum at low x. For oxygen concentration greater than ${x}_{c}$, the valence-band maximum is defined by the onset of the O 2p lone-pair states. Structures of the valence bands are discussed in the light of recent band-structure calculations. The Fermi level is seen to shift by 0.7 eV between x=0 and x=2 towards the conduction-band edge. The natural valence-band offset between a-Si and a-${\mathrm{SiO}}_{2}$ was determined to be 4.5 eV.
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TL;DR: In this paper, high-resolution x-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures for a series of high-k materials (HfO2)x(Al2O3)1−x grown on (100) Si substrate with different HfO 2 mole fraction x.
Abstract: High-resolution x-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures for a series of high-k materials (HfO2)x(Al2O3)1−x grown on (100) Si substrate with different HfO2 mole fraction x. Al 2p, Hf 4f, O 1s core levels spectra, valence band spectra, and O 1s energy loss all show continuous changes with x in (HfO2)x(Al2O3)1−x. These data are used to estimate the energy gap (Eg) for (HfO2)x(Al2O3)1−x, the valence band offset (ΔEν) and the conduction band offset (ΔEc) between (HfO2)x(Al2O3)1−x and the (100) Si substrate. Our XPS results demonstrate that the values of Eg, ΔEν, and ΔEc for (HfO2)x(Al2O3)1−x change linearly with x.
300 citations
TL;DR: In this paper, the valence band density of electron states shows a lone pair band and a deeper bonding band as usual, impurities have a greater effect in the nitride than in conventional lone pair semiconductors.
Abstract: Silicon Nitride is found to have a valence band maximum of nitrogen lone pair p electrons because of the planar nitrogen site. This contrasts with the usual lone pair semiconductors, such as SiO2, caused by a p4 valence configuration. Consequently although the valence band density of electron states shows a lone pair band and a deeper bonding band as usual, impurities have a greater effect in the nitride than in conventional lone pair semiconductors. Hole transport is also discussed.
246 citations
TL;DR: It is found that ALD on MoS2 bulk material is not uniform and surface functionalization will be required before controllable and low defect density high-κ/MoS2 interfaces will be realized.
Abstract: We report our investigation of the atomic layer deposition (ALD) of HfO2 on the MoS2 surface. In contrast to previous reports of conformal growth on MoS2 flakes, we find that ALD on MoS2 bulk material is not uniform. No covalent bonding between the HfO2 and MoS2 is detected. We highlight that individual precursors do not permanently adsorb on the clean MoS2 surface but that organic and solvent residues can dramatically change ALD nucleation behavior. We then posit that prior reports of conformal ALD deposition on MoS2 flakes that had been exposed to such organics and solvents likely rely on contamination-mediated nucleation. These results highlight that surface functionalization will be required before controllable and low defect density high-κ/MoS2 interfaces will be realized. The band structure of the HfO2/MoS2 system is experimentally derived with valence and conduction band offsets found to be 2.67 and 2.09 eV, respectively.
237 citations
TL;DR: In this paper, the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy is proved to be valid for determining the bandgap of (AlGa)2O3 films.
Abstract: Bandgap tunable (AlGa)2O3 films were deposited on sapphire substrates by pulsed laser deposition (PLD). The deposited films are of high transmittance as measured by spectrophotometer. The Al content in films is almost the same as that in targets. The measurement of bandgap energies by examining the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy is proved to be valid for determining the bandgap of (AlGa)2O3 films as it is in good agreement with the bandgap values from transmittance spectra. The measured bandgap of (AlGa)2O3 films increases continuously with the Al content covering the whole Al content range from about 5 to 7 eV, indicating PLD is a promising growth technology for growing bandgap tunable (AlGa)2O3 films.
179 citations
TL;DR: In this paper, the structure, optical absorption and photoluminescence properties of SiOx films subjected to thermal annealing at 750-1100°C were investigated, and Si crystallites with a few nanometers in size were observed in the SiO1.3 and SiO 1.65 films.
Abstract: Structure, optical absorption and photoluminescence (PL) properties of SiOx films subjected to thermal annealing at 750–1100 °C are investigated. Si crystallites with a few nanometers in size are observed in the SiO1.3 and SiO1.65 films annealed at 1100 °C. Threshold energies in optical absorption of the Si nanocrystallites are higher than that for bulk Si, suggesting a contribution from quantum confinement effects. The PL spectrum shows a remarkable increase in intensity after annealing at temperatures above 1000 °C. This PL behavior is closely related to the formation of Si nanocrystallites by the annealing. The PL peak energy of the annealed films shifts to higher energy with decreasing crystallite size but does not follow the blueshift for the absorption threshold energy. These results suggest that a localized state contributes to the PL mechanism. The SiO1.8 film annealed at 1100 °C, which contains no Si crystallites, exhibits an intense PL similar to the annealed SiO1.3 and SiO1.65 films. It is impl...
169 citations