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In this work, photoelectron spectroscopy is used to characterize the band alignment of lanthanum aluminate heterostructures which possess a wide range of potential applications. It is found that our experimental slope parameter agrees with theory using the metal-induced gap states model while the interface induced gap states (IFIGS) model yields unsatisfactory results. We show that this discrepancy can be attributed to the correlation between the dielectric work function and the electronegativity in the IFIGS model. It is found that the original trend, as established largely by metals, may not be accurate for larger band gap materials. By using a new correlation, our experimental data shows good agreement of the slope parameter using the IFIGS model. This correlation, therefore, plays a crucial role in heterostructures involving wider bandgap materials for accurate band alignment prediction using the IFIGS model. [ABSTRACT FROM AUTHOR]

The electric field strength of interface dipoles cannot be measured directly but can be derived from measurable electronic properties such as the valence band offset (VBO) and electron affinity using photoemission techniques. In this study, we found that the measurements of these two values are affected by differential charging and surface contaminants, respectively. This can affect both the polarity and the strength of the derived interface dipole and therefore might have implications regarding the understanding of oxide-semiconductor band alignment. Our overall band lineup and derived interface dipole in lanthanum aluminate (LAO) heterostructures agree excellently with a popular charge-neutrality level model. This would not be possible without the accurate measurement of VBO and electron affinity in LAO heterostructures. [ABSTRACT FROM AUTHOR]

By direct atomic nitrogen (N) doping, high concentration of N is incorporated into TiO2 and the doping effects are investigated. High resolution x-ray photoelectron spectroscopy core-level spectra indicate N substitution for O and formation of Ti-N bonds. Different Ti valent states are found at different N concentrations. Although the shape of the valence spectra changes significantly up on N doping, the band gap narrowing effect is insignificant. First-principles calculations confirm formation of Ti 3d gap states when N concentration exceeds 1 at. %, which leads to pinging of N 2p states in the band gap. [ABSTRACT FROM AUTHOR]

Cu2O thin films are deposited by direct current reactive magnetron sputtering on borofloat glass and indium tin oxide (ITO) coated glass at room temperature. The effect of oxygen partial pressure on the structures and properties of Cu2O thin films are investigated. We show that oxygen partial pressure is a crucial parameter in achieving pure phases of CuO and Cu2O. Based on this finding, we fabricate heterojunctions of p-type Cu2O with n-type gallium doped ZnO (GZO) on ITO coated glass substrates by pulsed laser deposition for GZO thin films. The energy band alignment for thin films of Cu2O/GZO on ITO glass is characterized using high-resolution x-ray photoelectron spectroscopy. The energy band alignment for the Cu2O/GZO heterojunctions is determined to be type II with a valence band offset of 2.82 eV and shows negligible effects of variation with gallium doping. The higher conduction band of the Cu2O relative to that of GZO in the obtained band alignment shows that the heterojunctions are suitable for solar cell application based on energy levels consideration. [ABSTRACT FROM AUTHOR]

SnO2 films with a thickness around 150 nm were deposited on the (111) surface of a SrTiO3 single crystal substrate by laser molecular beam epitaxy technique in a temperature range 600–750 °C and oxygen pressure from 10-3 to 1 Pa, respectively. The growth behavior was in situ monitored by reflection high-energy electron diffraction, and the epitaxial relations were further investigated by ex situ x-ray diffraction measurement in different geometries. All the films were confirmed to be highly (200) oriented showing good crystalline quality, despite the large lattice mismatch between SnO2 and SrTiO3. Based on the crystallographic model and structure analysis, six equivalent directions in the SrTiO3 (111) surface for the nucleation of SnO2 were discovered, which confirmed the existence of sixfold symmetrical domains in the SnO2 epilayer. Additionally, the optical dielectric function of the SnO2/SrTiO3 epitaxial film was simulated by the Tauc–Lorentz–Drude model in the UV-vis-NIR region. [ABSTRACT FROM AUTHOR]

In this work, we investigate the changes in the band offsets of lanthanum aluminate on silicon after postdeposition annealing at 600 and 800 °C by x-ray photoelectron spectroscopy (XPS). It is found that annealing at 800 °C reduces the conduction band offset from 2.31 to 1.39±0.2 eV. A detailed analysis is performed to ascertain the origin of the changes. We will show that the observed band offset changes are not a consequence of alterations in the bulk properties of the oxide film, but rather a true band alignment change between the two materials. After systematically considering “artefacts” of XPS measurements, including extra-atomic relaxation and differential charging, we conclude that the band offset changes originate mainly from an interfacial effect. While intrinsic gap states dipoles are not sufficient to account for the large band offset shifts, we turned our attention to examine the interface of the gate oxide stack. We show the existence of at least two types of dipoles. One of the dipoles exists at the silicon-silicon oxide interface, while the strength of the other dipole can be correlated with the thickness and the chemical stoichiometry of the interfacial silicate. [ABSTRACT FROM AUTHOR]

The effect of substrate temperature (TS) on the behavior of field emission, microstructure, optical band gap, and the surface energy of N-doped SrTiO3 thin films coated on silicon tip arrays has been examined in detail. Results indicate that the TS dominates the chemical states of nitrogen added to the sputtered SrTiO3 films and hence the observations. At the critical temperature of 600 °C, nitrogen atoms incorporate into the oxide film with sp-hybridization features. The generation of the nonbonding lone pair states narrows the optical band gap and the lone pair induced antibonding dipoles lower the threshold field for electron emission substantially. At lowered TS, molecular adsorption of nitrogen dominates. Contact angle measurements further evidence for the presence of antibonding dipole states at the surfaces which is responsible for the adsorbate-induced surface stress. [ABSTRACT FROM AUTHOR]

In this work, we examine the valence band offset of hafnium aluminate (HfAlO), a material of interest for use as a high dielectric constant (high-k) gate oxide, following postdeposition annealing. It is observed that annealing leads to a change in the band offset between the high-k oxide and the semiconductor. Our results conclusively show that the change is due to the existence of an electrostatic dipole field at the interface between HfAlO and the silicon substrate. This provides evidence to partly account for the observed flatband voltage shifts in high-k dielectric stack structures in the literature. The origin of the dipole field is also discussed in terms of the interfacial permittivity. [ABSTRACT FROM AUTHOR]

In this work, we report on the band offsets of yttrium oxide (Y2O3) on various relaxed and strained semiconductor substrates, such as silicon (Si), germanium (Ge), and silicon germanium (SiGe). By using the example of Y2O3/Si, important experimental aspects in using photoemission to determine band offsets are discussed. We then discuss the various values of band offsets of Y2O3 on the different substrates that we obtained by using x-ray photoelectron spectroscopy. Finally, we show that presputtering 3 Å of metallic Y [equivalent to 1 ML (monolayer) coverage] before the deposition of Y2O3 affects the band lineup by reducing the resultant valence band offsets. We explain the observed band offsets by using an interfacial layer model. [ABSTRACT FROM AUTHOR]

The effect of nitrogen (N) doping on the behavior of field emission, surface energy and the band structure of strontium titanate (SrTiO3) thin films coated on silicon tip arrays has been examined in detail. Measurements using x-ray photoelectron spectroscopy, ellipsometry, water contact angle and field emission testing revealed that the optimal 50%-nitrogen partial pressure (PN) could improve substantially the threshold field of electron emission of the SrTiO3 films accompanied with narrowed band gap, lowered surface energy and work function and a negative energy shift of the N 1s level from 404 to 396 eV. Results evidence consistently the presence of the nonbonding lone pairs and the lone pair induced antibonding dipoles upon tetrahedron formation which is responsible for the observations. At PN below and above the optimal value physisorption and hydrogen bond likes formation like to occur. [ABSTRACT FROM AUTHOR]

(Ba0.65Sr0.35)1-xLaxTiO3 (BSLT) thin films with different La concentrations have been deposited on Si field emitter arrays (FEAs) using sol-gel technology for field electron emission applications. The films exhibit the perovskite structure at low La substitution level (x≤0.5) and the pyrochlore phase at high La concentration (x≥0.75). The 30-nm-thick BSLT (x=0.25) thin film has higher crystallinity of perovskite structure in the surface region. An x-ray photoelectron spectroscopy study indicates that the oxygen vacancy concentration decreases with La substitution. With respect to the undoped Ba0.65Sr0.35TiO3 thin film, the Fermi level shifts down for the BSLT sample with x=0.1 ascribed to the decreasing oxygen vacancy concentration, and then shifts up for the BSLT sample with x=0.25 attributed to the increasing La substitution level. In highly doped films with an x value over 0.5, it shifts down again associated with the second pyrochlore phase formation. The best enhancement in field emission is found for the BSLT-coated (x=0.25) Si FEAs due to the improved perovskite structure in the surface region and up-moved Fermi level of the coating. [ABSTRACT FROM AUTHOR]

(CeO[sub y])[sub 0.67](Al[sub 2]O[sub 3])[sub 0.33] (1.5≤y≤2) (CeAlO[sub x]) thin films were deposited on p-type Si (100) substrates by the pulsed laser deposition method at 650 °C. The effect of oxygen pressure on structural and thus dielectric properties of the CeAlO[sub x] films was extensively investigated. The CeAlO[sub x] thin films turned from a mixture of crystalline CEO[sub 2], Ce[sub 2]O[sub 3], and Al[sub 2]O[sub 3] to the amorphous CeAlO[sub 3] as the deposition oxygen pressure was decreased from 3.2 × 10[sup -2] to 4.5 × 10[sup -6] mbar. With decreasing oxygen pressure, Ce[sup 4+] content decreased while Ce[sup 3+] content increased. The reduction of Ce[sup 4+] to Ce[sup 3+] compensated the oxygen deficit as a result of the decreased oxygen pressure. The flatband voltage (V[sub FB]) of the CeAlO[sub x] thin films decreased with oxygen pressure due to the decreased fixed charges in the films. The increased leakage current density of films as a result of the reduction in oxygen pressure was probably attributed to the electron hopping conduction between Ce[sup 4+] and Ce[sup 3+] at middle pressure and poor leakage property of Ce[sub 2]O[sub 3] at low pressure, respectively. [ABSTRACT FROM AUTHOR]

We report a systematic study of the effects of wet chemical treatment, inductively coupled plasma etching, and thermal annealing on the surface and optical properties of Mg-doped p-type GaN. The chemical bonding and surface stoichiometry of the GaN surface subjected to different processing steps are analyzed based on the results of x-ray photoelectron spectroscopy. Atomic force microscopy has been employed to characterize the surface morphology. Photoluminescence (PL) and micro-Raman techniques have been used to investigate the electronic and vibrational properties of plasma etched surface. We have correlated the surface changes induced by dry etching of p-type GaN to the corresponding changes in the defect and impurity related states, through their manifestation in the PL spectra. We have observed several local vibrational modes (LVMs) in p-type GaN subjected to various processing steps. A broad structure in the low-temperature Raman spectra around 865 cm[sup -1] is attributed to the electronic Raman scattering from neutral Mg acceptors. In addition to the LVMs of Mg-H[sub n] complexes, two new modes near 2405 and 2584 cm[sup -1] are observed from the etched p-GaN surface. We have also carried out PL and micro-Raman analyses of Mg-doped GaN films annealed under different conditions. [ABSTRACT FROM AUTHOR]

Examines the argon (Ar) incorporation and surface compositional changes in InP(100) after keV Ar[sup+] bombardment at various ion fluences, using angle-resolved x-ray photoelectron spectroscopy. Applications of Ar[sup+] beams; Advantages of Ar[sup+] beams; Comparison between the properties of InP and gallium arsenide; Discussion on the surface characterization of InP following Ar[sup+] sputtering; Difference between indium and phosphorus atoms.

Presents information on a study that calculated the total energy and electronic structure of the hexagonal-closed-packed Ni[sub75]Ta[sub25] metastable phase by the self-consistent discrete variational method and the local X α exchange approximation. Description on the theoretical method; Results and discussion on the study; Conclusion.

Presents information on a study which examined the incorporation of argon and the formation of silicon (Si) carbide during low energy argon-ion bombardment of Si(100). Experimental procedure; Results and discussion; Conclusion.

We report on the growth of two-dimensional (2D) WS2 on high-k HfO2/Si substrates by reactive sputtering deposition. Raman, x-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy characterizations indicate that the 2D WS2 layers exhibit high-quality crystallinity and exact stoichiometry. Through high-resolution XPS valence spectra, we find a type I alignment at the interface of monolayer WS2/HfO2 with a valence band offset (VBO) of 1.95 eV and a conduction band offset (CBO) of 1.57 eV. The VBO and CBO are also found to increase up to 2.24 eV and 2.09 eV, respectively, with increasing WS2 layers. This is consistent with the results obtained from our first-principles calculations. Our theoretical calculations reveal that the remarkable splitting and shift of the W 5 d z 2 orbital originating from interlayer orbital coupling in thicker WS2 films induce a reduction of its bandgap, leading to an increase in both the VBO and CBO. This observation can be attributed to the asymmetric splitting at different high symmetric k-points caused by the interlayer orbital coupling. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy was used to investigate thermal stability of HfO2 on SiO2/Si substrate prepared by atomic layer deposition, followed by annealing at different temperature. Hf silicate and Hf silicide are formed at the interface of HfO2 and SiO2 during deposition. The Hf silicide disappears, while the amount of the Hf silicate is intensified after post-deposition annealing treatment at 400 °C. Phase separation of the Hf silicate layer occurs when the annealing temperature is over 400 °C, resulting in the Hf silicate decomposition into Si and Hf oxides. Moreover, crystallization at high temperature leads to grain boundaries formation, which deteriorates the gate leakage current, as observed by the electrical measurements. The similar annealing temperature dependence of both internal electric field and the amount of Hf silicate implies that the Hf silicate plays a key role in building up the internal electric field, which is attributed to generation of oxygen vacancies ( V o) in the Hf silicate layer. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]