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Understanding the energy alignment of electronic bands, which originate from ultrathin MoS2 layers and metal electrodes attached to them, is crucial for the design of MoS2-based electronic devices. We have applied internal photoemission spectroscopy (IPE) to analyze this alignment. We demonstrate that IPE can yield the barrier heights in the metal/ two-dimensional semiconductor/insulator stacks when the top metal electrode is sufficiently thin for allowing both the photoexcitation of electrons and their transport towards the insulator. The electron barrier at the interface between Al and monolayer (1ML) of MoS2 is estimated at 0.7 eV, and this value explains the experimentally observed attenuated quantum yield contribution from the aluminum. Based on the relative energies of the low-energy threshold position and the Fermi level of aluminum at the interface with the SiO2 insulator, we provide a simple explanation for the observed current photoinjection at the interface between aluminum and 1ML MoS2.

Using first-principles calculations based on density functional theory, we study the magnetic and electronic properties of hole-doped two-dimensional InSe. Our simulations reveal that although 2D InSe is intrinsically nonmagnetic, a stable ferromagnetic phase appears for a wide range of hole densities. Interestingly, hole doping induces not only spontaneous magnetization but also half-metallicity, and hole-doped InSe, presenting one conducting and one insulating spin channel, could be highly promising for next generation spintronic nanodevices. The possibility of inducing hole doping and a subsequent ferromagnetic order by intrinsic and extrinsic defects was also investigated. We found that In vacancy creates spin-polarized states close to the valence band and leads to a p-type behavior. Similar to In vacancies, group-V atoms replacing Se atoms lead to a p-type behavior, potentially stabilizing a ferromagnetic order in 2D InSe.

integration requires development of low thermal budget process modules. High-quality SiO 2 interfacial layer (IL), obtained up to now only by high-temperature (≥850°C) oxidation or exposure, is crucial for pMOS NBTI reliability. In unannealed IL’s grown at reduced temperatures, we show that unrelaxed interface strain induces high defect densities, with physics-based NBTI modeling suggesting excessive hydroxyl-E’ defect formation due to Si-O bond stretch. Based on ab-initio theoretical insights, we demonstrate an atomic hydrogen treatment to passivate SiO 2 defects at low temperatures (100-300°C), which is shown to be vastly more effective than high pressure molecular hydrogen exposure, and to yield an SiO 2 quality and reliability surpassing a 900°C oxide.

We present fundamental exploration of inorganic dielectric wafer-to-wafer (W2W) bonding by electron spin resonance (ESR) to assess the function of dangling bond-type interface defects. As compared to a standard PECVD SiO2 which contains negligible dangling bonds (DBs), it is found that a substantial amount of silicon and carbon types of DBs, as high as 1014 cm-2, are present in the pre-bonding layer of SiCN and SiCO, mainly as a result of surface modification by means of low energy plasma activation prior to bonding. It is inferred that the evolution of DBs has a positive influence on improving the wafer bonding energy during post-bond anneal, in that the results suggest that a decrease of DBs translates into the formation of chemical bonds at the bonding interface.

The article overviews experimental results obtained by applying internal photoemission (IPE) spectroscopy methods to characterize electron states in single- or few-monolayer thick two-dimensional materials and at their interfaces. Several conducting (graphene) and semiconducting (transitional metal dichalcogenides MoS2, WS2, MoSe2, and WSe2) films on top of thermal SiO2 have been analyzed by IPE, which reveals significant sensitivity of interface band offsets and barriers to the details of the material and interface fabrication, indicating violation of the Schottky-Mott rule. This variability is associated with charges and dipoles formed at the interfaces with van der Waals bonding as opposed to the chemically bonded interfaces of three-dimensional semiconductors and metals. Chemical modification of the underlying SiO2 surface is shown to be a significant factor, affecting interface barriers due to violation of the interface electroneutrality. ispartof: JOURNAL OF PHYSICS-CONDENSED MATTER vol:32 issue:41 ispartof: location:England status: published

Identification of two-dimensional (2D) materials with magnetic properties has received strong research attention in the development of advanced spin-based devices. By means of first-principles calculations, we investigate the stability, electronic properties, and the hole-doping-induced magnetic properties of metal oxide ($M\mathrm{O}, M=\mathrm{Ga},\mathrm{In}$) monolayers. They are intrinsically nonmagnetic stable semiconductors, with high energetic, vibrational, and thermal stability. Hole doping can switch them from nonmagnetic to ferromagnetic and turn them into half-metals over a wide range of hole densities. Monte Carlo simulations predict that the highest Curie temperature of the GaO monolayer can reach \ensuremath{\sim}125 K. Our results indicate that monolayer $M\mathrm{O}$ could be eligible candidate materials for 2D spintronic devices.

Exfoliated flakes from molybdenite crystals often still serve as benchmark substrates for two-dimensional MoS2 fundamental and device-oriented research. In this article, results are reported of a multi-frequency electron paramagnetic resonance (EPR) study on a series of natural 2H MoS2 crystals taken from various (seven) geological sites with the intent to explore the variations in quality and properties in terms of occurring paramagnetic point defects, with particular focus on the assessment of the predominant type of impurity dopant. The sample set covers three types of overall doping regimes, i.e., p-type, n-type, and mixed (n-type and p-type parts in one sample). The doping type appears primarily governed by substitutional impurities as evidenced by the observed As and N acceptor (both substituting for S) and Re donor (substituting for Mo) signals. For all p-type specimens, doping is found to be ruled by As where, however, a strong variation is revealed in doping uniformity, which appears not directly correlated with the As dopant density. Without specific precautions taken, surface contamination related EPR signals are observed in virtually all As-excavated geo-MoS2 specimens. While several of these signals are of unassigned origin, two prominent ones are identified, one as concerning oxo-Mo5+ compounds and the other Mn2+ centers. The geo-MoS2 sample with the foremost n-type doping shows, besides the prime Re donor EPR signal, an intense powder-pattern signal, tentatively typified by g∥ = 2.076, g⊥ = 2.253, which is suggested to originate from intercalation-related defects. The results bear out the necessity of rigorous surface cleaning, even including invasive removal of surface layers, to obtain pristine MoS2 parent crystals suitable for enabling exfoliation of high quality flakes. ispartof: JOURNAL OF CHEMICAL PHYSICS vol:152 issue:23 ispartof: location:United States status: published

Hole-doping of GaX, InX (X = S or Se) and SnO monolayers is predicted to induce a stable ferromagnetic order in these two-dimensional materials, making them potentially interesting for nanoscaled spintronic devices. Ferromagnetism in these materials arises from their peculiar Mexican-hat valence band edge structure, which leads to a Stoner instability. We discuss here the results from first-principles simulations on the p-type doping-induced ferromagnetism in these 2D materials. Hole-doping, induced by intrinsic and extrinsic point defects, is considered. Metal vacancies are found to produce shallow spin-polarized gap states near the valence band edge, leading to a p-type behavior. Among the investigated potential extrinsic defects (dopants), As substitution of the oxygen atoms in SnO or Bi substitution of the selenium atoms in InSe appears to be good candidates for the hole-doping of these 2D materials.

The high contact resistance at metal/two-dimensional (2D) semiconductor junctions is a major issue for the integration of 2D materials in nanoelectronic devices. We review here recent theoretical results on the contact resistance at lateral heterojunctions between graphene or 1T-MoS2 with 2H-MoS2 monolayers. The transport properties at these junctions are computed using density functional theory and the non-equilibrium Green’s function method. The contact resistance is found to strongly depend on the edge contact symmetry/termination at graphene/2H-MoS2 contacts, varying between about 2 × 102 and 2 × 104 Ω∙μm. This large variation is correlated to the presence or absence of dangling bond defects and/or polar bonds at the interface. On the other hand, the large computed contact resistance at pristine 1T/2H-MoS2 junctions, in the range of 3–4 × 104 Ω.μm, is related to the large electron energy barrier (about 0.8 eV) at the interface. The functionalization of the metallic 1T-MoS2 contact by various adsorbates is predicted to decrease the contact resistance by about two orders of magnitude, being very promising for device applications.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. Dangling bond defects (DBs) in silicon-passivated (1- or 3-nm thick Si cap) strained-(100)Si 1−x Ge x (x = 0.25–0.55) layers at interfaces with 1.8-nm thick HfO 2 gate dielectric are studied by means of Electron Spin Resonance (ESR) spectroscopy. The results suggest a dominant contribution of Si DBs (P b0 centers), a considerable fraction of which is located at the interface between the Si substrate crystal and the pseudomorphic Si 1−x Ge x film. The density of Si DBs in the Ge containing samples is significantly lower than at the reference (100)Si/ HfO 2 interface and decreases below the ESR detection limit (≈ 0.8 × 10 11 cm −2 ) with increasing thickness and Ge concentration in the Si 1−x Ge x layer. However, the beneficial effect of Ge becomes less pronounced when the thickness of the Si cap is reduced to 1 nm or in the case of direct deposition of HfO 2 on top of uncapped Si 1−x Ge x . From these observations we conclude that DBs are eliminated due to in-diffusion of Ge from the Si 1−x Ge x channel into interfacial Si layers, bringing the concentration of Ge to the range in which generation of Si DBs becomes energetically unfavourable, in agreement with previous observations on condensation-grown Si 1−x Ge x layers. ispartof: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS vol:31 issue:1 ispartof: location:FRANCE, Strasbourg status: Published online

The contact resistance at metal/two-dimensional (2D) semiconductor heterojunctions is currently a major issue for the integration of 2D materials in new generations of nanoelectronic devices. In this chapter, the contact resistance at graphene/MoS2 and 1T/2H-MoS2 heterostructures is computed using first-principles simulations, based on density-functional theory and the nonequilibrium Green's function method. The contact resistance, RcW, is found to strongly depend on the edge contact symmetry/termination at graphene/MoS2 contacts, varying between about 2 × 102 and 2 × 104 Ω μm. This large variation in RcW is correlated to the presence or absence of dangling bond defects and/or polar bonds at the interface. On the other hand, the large computed contact resistance at pristine 1T/2H-MoS2 contacts, in the range of 3–4 × 104 Ω μm, is related to the large electron energy barrier (about 0.8 eV) at the interface. The functionalization of the metallic 1T-MoS2 contact by various adsorbates is predicted to decrease the contact resistance by about two orders of magnitude, being promising for device applications.

In this article, heat-activated persulfate oxidation was investigated as a promising technique for the removal of sulfamethoxazole from an aqueous environment. It was found that the degradation efficiency of sulfamethoxazole increases with increasing persulfate concentration due to the increased •SO4- production. As suggested by the Arrhenius equation, the sulfamethoxazole degradation rate constant increased with increasing temperature. An activation energy of 103 kJ/mol was determined. Furthermore, the initial pH of the reaction mixture had a large influence on the degradation of sulfamethoxazole. At higher initial pH values, the degradation of sulfamethoxazole increased. The main cause for this increase is a difference in sulfamethoxazole distribution: at higher pH, the deprotonated form of sulfamethoxazole is present and found to be more susceptible to degradation. A second reason was found to be the formation of •OH at higher initial pH values, although this contribution was smaller. To elucidate the degradation process, six intermediates were identified, and the difference in formation of these compounds at different initial pH values was revealed. Through ECOSAR modeling, some degradation products were found to be of main interest when monitoring the toxicity of the degradation mixture. ispartof: Chemical Engineering Journal vol:379 status: Published online

Silicene, the silicon counterpart of graphene, has been successfully grown on metallic substrates such as Ag(111), ZrB2(0001), and Ir(111) surfaces. However, characterization of its electronic structure is hampered by the metallic substrate. In addition, potential applications of silicene in nanoelectronic devices will require its growth on or integration with semiconducting and insulating substrates. We herein present a review of recent theoretical works regarding the interaction of silicene with non-metallic templates, distinguishing between the weak van-der-Waals-like interactions of silicene with, for example, layered metal (di)chalcogenides, and the stronger covalent bonding between silicene and, for example, ZnS surfaces. We then present a methodology to effectively compare the stability of diverse silicene structures using thermodynamics and molecular dynamics density functional theory calculations. Recent experimental results on the growth of silicene on MoS2are also reported and compared to the theoretical predictions.[Figure not available: see fulltext.]

Battery safety and cycle life remain of concern to current Li-ion batteries that use a liquid organic electrolyte. Both issues can be resolved by employing a solid electrolyte. Numerous Li-ion conducting solids are known today, however the stability of most of these is too low to engender widespread usage. Here, we report on the decomposition chemistry and electrochemistry of LiPON, at present the most commonly used solid electrolyte. The decomposition potential was calculated from basic thermodynamic quantities and was linked to current–voltage (I–V) measurements with great consistency. The decomposition of LiPON was shown to occur at a potential of 4.3 V and proceeds in a diffusion limited way. The LiPON layer decomposes into Li-ions, O2 or N2 gas and a phosphate rich compound. Ultimately hard breakdown could occur through the formation of metallic lithium filaments that short circuit the LiPON layer as shown by TOF-SIMS imaging experiments. As such the work provided here also provides insight in the breakdown mechanism of RRAM devices.

Nature of gap states in chalcogenide semiconductors GexSe1-x is studied by combining X-ray photoelectron (XPS) and absorption (NEXAFS) spectroscopy with photoconductivity (PC) and internal photoemission (IPE) measurements at the semiconductor/insulator interface. It is shown that studied GexSe1-x layers are heterogeneous composite-like matrices and the gap states determining electron transport originate from formation of homopolar Ge-Ge bonds. Nanoscale phase separation effect is revealed manifesting in redistribution of GeSe2 and GeSe networks, respectively, with increase of Ge content with predominant contribution of GeSe.

© 2017 Elsevier B.V. Several native point defects in MoS 2 are theoretically studied, using first-principles simulations. The isotropic g-values of these defects are computed, and compared to recently reported experimental results, obtained from electron spin resonance experiments performed on MoS 2 layers synthesized by the sulfurization of Mo films. We tentatively assign the observed electron spin resonance signal with isotropic g-value of 2.002 to a sulfur antisite defect. This defect presents energy levels in the MoS 2 band-gap, and could hamper the proper functioning of MoS 2 -based field effect transistors. We next study the interaction of H 2 molecules with the sulfur antisite defect, using first-principles molecular dynamics simulations and the nudged elastic band method. Our results predict that this defect can be passivated by hydrogen, with a computed activation energy of about 1.5 eV. ispartof: Applied Surface Science vol:416 pages:853-857 status: published

Two dimensional (2D) materials are currently attracting considerable interest due to their promising applications in future nanoelectronic devices. Magnetic 2D materials are also gaining attention, for their possible use in novel spintronic devices [1]. Recently, hole-doping in monolayer SnO has been theoretically predicted to induce a paramagnetic to ferromagnetic phase transition in this 2D material, for a typical hole density of about 5x1013/cm2 [2]. Magnetism in monolayer SnO arises from an exchange splitting of electronic states at the top of the valence band, where the density of states exhibits a sharp van Hove singularity, resulting in a so-called Stoner (magnetic) instability [2]. This behavior is typical of materials with “Mexican-hat” energy band edges (as predicted for the valence band edge of monolayer SnO), and has also been predicted in e.g. monolayer GaSe [3]. In this work, the possibility to induce hole doping in monolayer SnO by intrinsic and extrinsic defects is investigated, using first-principles simulations, based on density functional theory. It is found that Sn vacancies generate spin-polarized gap states near the valence band edge of monolayer SnO, and that these point defects are behaving like acceptors. A typical density of 5x1013/cm2 of Sn vacancies induces a paramagnetic to ferromagnetic phase transition in the material, with a magnetic moment density of 1 Bohr magneton/hole. Substitutional doping of Sn atoms by e.g. In or Zn atoms is also predicted to result in hole-doping of monolayer SnO, and also leads to a ferromagnetic order in the 2D material. The possibility to induce a ferromagnetic phase transition in monolayer SnO by electrostatic doping will also be discussed. [1] W. Han, APL Mater. 4, 032401 (2016). [2] L. Seixas et al., Phys. Rev. Lett. 116, 206803 (2016). [3] T. Cao et al., Phys. Rev. Lett. 114, 236602 (2015).

We report on the results of low-temperature K- and Q-band electron spin resonance (ESR) measurements on three types of device-grade HfO2 films deposited on p-(100)Si by chemical vapor deposition (CVD) using different precursors. The study has been carried out in combination with ex situ contactless charge injection, complemented with various post-growth irradiation treatments, with the intent to assess the presence and atomic nature of occurring charge trapping centers. In HfO2 layers grown by atomic layer (AL) and metal-organic (MO) CVD, this reveals the reproducible appearance of a paramagnetic center, termed H5, in firm correlation with alternate positive/negative charge injection, i.e., distinct signal intensity increase/decrease, respectively. Simulation of the observed powder pattern for both K- and Q-band consistently points to a defect of orthorhombic symmetry characterized by g1=1.880±0.006, g2=1.900±0.006, g3=1.981±0.0015. Analysis based on the inferred spectroscopic ESR characteristics in comparison with previous theoretical work leads to the suggestion that the observed center may concern an O-vacancy defect, closest perhaps to the 4-fold 1+charged O-vacancy (VO4 + ). The revealed defect may account, at least partly, for the previously reported distinct propensity of positive charge trapping in Si/hafnia structures grown by ALCVD and MOCVD. ispartof: Microelectronic Engineering vol:178 pages:112-115 ispartof: location:Potsdam: GERMANY status: published

Such technologically abundant agent as hydrogen has a strong effect on the metal/oxide interface energy barrier. Internal photoemission analysis of electron barrier height variations at Pt/HfO2 interfaces caused by annealing in hydrogen reveals the formation of a significant (≥0.4 eV) electrostatic dipole layer. The orientation of the H-induced dipole appears to be sensitive to the growth conditions and treatments, e.g., Hf precursor used in the atomic layer deposition (ALD) process: In the case of the HfCl4 precursor, annealing in H2 leads to barrier lowering, whereas the barrier becomes higher in samples grown by using tetrakis(dimethylamido)hafnium. These findings indicate that hydrogen may form dipoles of opposite orientation through two different mechanisms: The positive dipole is caused by H interaction with the metal surface, which can also be found at interfaces of Pt with other oxides such as SiO2 and Al2O3. By contrast, the sensitivity of the negative dipole formation to the HfO2 ALD chemistry suggests it to be related to a negatively charged bonded state of hydrogen in the near-interface oxide.Moreover, the formation of positive dipole is also observed after high temperature anneal in nitrogen suggesting the contribution of additional mechanisms of dipole formation. The work at KU Leuven was supported by Fonds Wetenschappelijk Onderzoek – Vlaanderen (Project G.0C05.13) and by the Internal Fund project C14/16/061. ispartof: Microelectronic Engineering vol:178 pages:304-307 ispartof: location:Potsdam: GERMANY status: published

Using first-principles calculations, we study the structural, energetic, and electronic properties of various point defects in arsenene. Stone-Wales defects are found to be thermodynamically favorable and are predicted to be stable at room temperature. Defects are found to significantly influence the electronic properties in buckled phase. In particular, single vacancies generate gap states whereas strain induced states close to the valence and conduction band edges are observed for Stone-Wales and di-vacancy defects. The computed band structures of di-vacancy defects in puckered phase are less disturbed compared to the corresponding band structures in the buckled one. The influence of a hydrogen-rich atmosphere on the electronic properties of defective arsenene is also investigated. Hydrogen termination of mono/di-vacancies is an exothermic process which removes all defect induced gap states.

A pentapeptide sequence was functionalized with an asymmetric arylated methyl-viologen (AVI3D2) and through controllable β-sheet self-assembly, conductive nanofibers were formed. Using a combination of spectroscopic techniques and conductive atomic force microscopy, we investigated the molecular conformation of the resultant AVI3D2 fibers and how their conductivity is affected by β-sheet self-assembly. These conductive nanofibers have potential for future exploration as molecular wires in optoelectronic applications. ispartof: CHEMICAL COMMUNICATIONS vol:55 issue:51 pages:7354-7357 ispartof: location:England status: published

Electron spin resonance (ESR) results are presented on the thermal stability and temperature dependence of the ESR spectral characteristics of the As acceptor dopant (As substituting for S site) in geological 2H-MoS2. Under sequential isochronal heating in H2 (1.1 atm), the As dopant density is found to remain unaffected for anneal temperatures (Tans) up to 525 °C, above which the density moderately decreases (∼3 times) for Tan → 840 °C. In turn, vacuum annealing is seen to result in a gradual increase (2–3 times) of the As acceptor density for Tan increasing from 400 °C→840 °C, pointing to a positive ‘regain’ of misconfigured As impurities in pristine geo-MoS2. Finally, meticulous monitoring of the ESR signal intensity versus tempertaure at X-band confirms the previously inferred As acceptor activation energy of 0.7±0.2 meV at K-band. The appropriateness of the latter ESR probing and analysis approach has been consolidated by application to the archetypal case of decoupled P donors in n-Si, resulting in an ESR-determined activation energy (42±4 meV) well in agreement with the generally accepted one. In light of these findings, As is confirmed as a promising candidate for stable covalently bonded p-type doping of MoS2. ispartof: Semiconductor Science And Technology vol:34 issue:3 status: published

© 2019 Elsevier B.V. Internal photoemission of electrons from uncapped monolayer graphene to insulating SiO 2 has been observed in samples prepared by water-intercalation based graphene transfer. The barrier height between the graphene Fermi level and the oxide conduction band bottom was reproducibly found to be 4.1–4.2 eV. Moreover, this value was weakly sensitive to the contacting metal work function (Al, Cu, Au). This barrier height corresponds to an effective work function of graphene close to 5.0 eV, which is nearly 0.5 eV higher than the usually reported vacuum value. ispartof: THIN SOLID FILMS vol:674 pages:39-43 status: published

The contact resistance at two-dimensional graphene/MoS2 lateral heterojunctions is theoretically studied, using first-principles simulations based on density functional theory and the nonequilibrium Green's function method. The computed contact resistance lies in the range of 102 to 104 Ω μm, depending on the contact edge symmetry (armchair or zigzag) and termination (Mo and/or S terminated). This large variation in the contact resistance arises from the variation in the interface barrier height, which is sensitive to the presence of polar C-Mo bonds or sulfur dangling bonds at the interface. These results highlight that the control of the edge symmetry and/or edge termination is crucial to achieve a low contact resistance (in the range of a few hundred ohms micrometer) at graphene/MoS2 lateral heterojunctions for 2D material-based field-effect devices. Part of this work was financially supported by the KU Leuven Research Funds, Project No. C14/17/080, as well as the 2DFun project, an ERA-NET project in the framework of the Graphene Flagship. The authors acknowledge the support from Flanders Innovation and Entrepreneurship.

© 2018 American Chemical Society. When two-dimensional (2D) group-VI transition metal dichalcogenides such as tungsten disulfide (WS 2 ) are grown by atomic layer deposition (ALD) for atomic growth control at low deposition temperatures (≤450 °C), they often suffer from a nanocrystalline grain structure limiting the carrier mobility. The crystallinity and monolayer thickness control during ALD of 2D materials is determined by the nucleation mechanism, which is currently not well understood. Here, we propose a qualitative model for the WS 2 nucleation behavior on dielectric surfaces during plasma-enhanced (PE-) ALD using tungsten hexafluoride (WF 6 ), dihydrogen (H 2 ) plasma and dihydrogen sulfide (H 2 S) based on analyses of the morphology of the WS 2 crystals. The WS 2 crystal grain size increases from ∼20 to 200 nm by lowering the nucleation density. This is achieved by lowering the precursor adsorption rate on the starting surface using an inherently less reactive starting surface, by decreasing the H 2 plasma reactivity, and by enhancing the mobility of the adsorbed species at higher deposition temperature. Since silicon dioxide (SiO 2 ) is less reactive than aluminum oxide (Al 2 O 3 ), and diffusion and crystal ripening is enhanced at higher deposition temperature, WS 2 nucleates in an anisotropic island-like growth mode with preferential lateral growth from the WS 2 crystal edges. This work emphasizes that increasing the crystal grain size while controlling the basal plane orientation is possible during ALD at low deposition temperatures, based on insight in the nucleation behavior, which is key to advance the field of ALD of 2D materials. Moreover, this work demonstrates the conformal deposition on three-dimensional (3D) structures, with WS 2 retaining the basal plane orientation along topographic structures. ispartof: CHEMISTRY OF MATERIALS vol:30 issue:21 pages:7648-7663 status: published

Scaling the planar NAND flash cells to the 20 nm node and beyond mandates introduction of inter-gate insulators with high dielectric constant (κ). However, because these insulators provide a smaller electron barrier at the interface with the poly-Si floating gate, the program window and the retention properties of these scaled cells are jeopardized. To reduce the charge loss from the floating to the control gate, one may consider the introduction of a hybrid floating gate (HFG) structure comprised of poly-Si and a high work function (WF) metal, e.g., TiNx (x ∼ 1; WF ∼ 4.7 eV) or Ru (WF ∼ 5.3 eV). However, the very HFG concept is based on the assumption that electron trapping occurs inside the HFG stack rather than on traps present in the high-κ insulator. To examine this critical hypothesis, we analyzed the energy distribution of electrons trapped in flash cells with poly-Si(2 nm)/TiN (6 nm)/Hf0.8Al0.2Ox(19 nm, κ ∼ 15–19)/TiNx (10 nm) and Si(2 nm)/Ru (1 nm)/Hf0.8Al0.2Ox(5 nm)/Al2O3 (5 nm)/Hf0.8Al0.2Ox (5 nm)/TiNx (10 nm) trapping gate stacks using the exhaustive photo-depopulation spectroscopy. We found that trapped electron energy levels show a broad distribution (± 0.3 eV) centred at ∼3.2 eV below the oxide conduction band. The energy onset of electron de-trapping at ∼2.8 eV matches the TiNx/HfO2 barrier height found from internal photoemission experiments, indicating that electrons are predominantly trapped inside the HFG.

Dry plasma etching, commonly used by the Photonics community as the etching technique for the fabrication of photonic nanostructures, could be a source of device performance limitations when used in the frame of silicon photovoltaics. So far, the lack of silicon solar cells with state-of-the-art efficiencies utilizing nanophotonic concepts shows how challenging their integration is, owing to the trade-off between optical and electrical properties. In this study we show that dry plasma etching results in the degradation of the silicon material quality due to (i) a high density of dangling bonds and (ii) the presence of sub-surface defects, resulting in high surface recombination velocities and low minority carrier lifetimes. On the contrary, wet chemical anisotropic etching used as an alternative, leads to the formation of inverted nanopyramids that result in low surface recombination velocity and low density of dangling bonds. The proposed inverted nanopyramids could enable high efficiency photonic assisted solar cells by offering the potential to achieve higher short-circuit current without degrading the open circuit voltage. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Internal photoemission of electrons from 4- and 2-monolayer thick MoS2 films prepared by sulphurization of metallic Mo on top of SiO2 or HfO2/SiO2 insulating stacks is detected. This enables determination of the energy position of the MoS2 valence band which is found to be at 4.1-4.2 eV below the SiO2 conduction band. At the interface with HfO2, a barrier height of 3.7 eV is found, corresponding to an increase of the electron affinity of MoS2 by 0.5 eV as compared to the SiO2 case. This suggests the presence of interface charges (or dipoles) in the interfacial HfO2 layer. publisher: Elsevier articletitle: Band alignment at interfaces of few-monolayer MoS2 with SiO2 and HfO2 journaltitle: Microelectronic Engineering articlelink: http://dx.doi.org/10.1016/j.mee.2015.04.106 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved. ispartof: Microelectronic Engineering vol:147 pages:294-297 ispartof: location:ITALY, Udine status: published

Graphical abstractDisplay Omitted Charge traps in (100)Ge/Sc2O3/HfO2 stacks are studied by ESR and electrical probing.The utility of Sc2O3 as passivation layer on Ge is studied by conventional ESR.Trapping centers in (100)Ge/Sc2O3 entities are tracked by ESR as g=2.0017 defects.Defect generation in (100)Ge/Sc2O3 entities may be suppressed by sufficient supply of O2.Oxygen deficiency causes thermal degradation of (100)Ge/Sc2O3/HfO2 stacks. The usefulness of employing the rare-earth Sc2O3 high-? (~16) dielectric in passivating Ge surfaces for metal-oxide-semiconductor device application is studied in terms of occurring inherent paramagnetic point defects, operating as detrimental charge traps. To assess their atomic nature, low temperature K-band electron spin resonance (ESR) experiments have been carried out in combination with electrical probing, including capacitance-voltage, internal photoemission and photoconductance observations, on (100)Ge/(GeO2)/Sc2O3/HfO2 stacks grown by atomic layer deposition subjected to various processing steps. In stacks with Ge directly contacted with Sc2O3, without an additional O-supply processing step, ESR reveals the presence of a prominent signal of powder pattern shape, centered at g=2.0017(2). It is ascribed to O-deficiency centers located in the Sc2O3-based dielectric, which from combined electrical analysis are concluded to be at the origin of substantial electron trapping (~6i?1012cm-2) in near-interfacial layers. Generally, the data suggest that O-deficiency caused by oxidation of Ge (O-scavenging) emerges as a crucial parameter in defect generation, leading to the conclusion that the suppression of defect generation will require a sufficient supply of oxygen during critical manufacturing steps.

There has been tremendous research effort in hunting for novel two-dimensional (2D) materials with exotic properties, showing great promise for various potential applications. Here, we report the findings about a new hexagonal phase of 2D Ga2O3 and In2O3, with high energetic stability, using a global searching method based on an evolutionary algorithm, combined with density functional theory calculations. Their structural and thermal stabilities are investigated by the calculations of their phonon spectra and by ab initio molecular dynamics simulations. They are predicted to be intrinsically non-magnetic stable semiconductors, with a flatband edge around the valence band top, leading to itinerant ferromagnetism and half-metallicity upon hole doping. Bilayer Ga2O3 is also studied and found to exhibit ferromagnetism without extra hole doping. The Curie temperature of these materials, estimated using Monte Carlo simulations based on the Heisenberg model, is around 40–60 K upon a moderate hole doping density.

Electron spin resonance (ESR) study on 2H-polytype synthetic MoS2 revealed the N acceptor dopants as being characterized by a spectrum of axial symmetry [g∥ = 2.032(2); g⊥ = 2.270(2)], typical for a hole-type center in MoS2. The N impurities substitute for S sites, with a density of ∼2.3 × 1017 cm−3, which accounts for the overall p-type doping. With respect to measurements for the applied magnetic field directed along the c-axis, the signal consists of a 14N primary hyperfine triplet of splitting constant A∥ = 14.7 ± 0.2 G superimposed on a correlated Gaussian single central line of peak-to-peak width ΔBpp = 15.3 ± 0.5 G, the latter making up only ∼26% of the total signal intensity. The current work extends on these results through extensive monitoring of the temperature (T) dependence of salient ESR parameters and studying the impact of thermal treatment. ESR signal saturation studies indicate a N acceptor spin–lattice relaxation time T1 (4.2 K) ≈ 3 × 10−4 s, notably different from the much smaller As acceptor’s T1 in geological MoS2. Concerning the thermal stability of the dopant, the N acceptor is found to be drastically passivated when exposed to H2 at ∼500 °C. Yet, subsequent reactivation attempts in vacuum at temperatures up to 740 °C appear unsuccessful, urging great caution with conventional forming gas treatments at T ≳ 500 °C. Combination of careful K- and Q-band ESR monitoring of the T-dependent signal intensity resulted in the consolidation of the N dopant as a shallow acceptor of activation energy Ea = 45 ± 7 meV. The consolidated results establish N as a promising candidate for stable covalently bonded p-type doping of MoS2 layers intended for application in novel nanoelectronic devices.Electron spin resonance (ESR) study on 2H-polytype synthetic MoS2 revealed the N acceptor dopants as being characterized by a spectrum of axial symmetry [g∥ = 2.032(2); g⊥ = 2.270(2)], typical for a hole-type center in MoS2. The N impurities substitute for S sites, with a density of ∼2.3 × 1017 cm−3, which accounts for the overall p-type doping. With respect to measurements for the applied magnetic field directed along the c-axis, the signal consists of a 14N primary hyperfine triplet of splitting constant A∥ = 14.7 ± 0.2 G superimposed on a correlated Gaussian single central line of peak-to-peak width ΔBpp = 15.3 ± 0.5 G, the latter making up only ∼26% of the total signal intensity. The current work extends on these results through extensive monitoring of the temperature (T) dependence of salient ESR parameters and studying the impact of thermal treatment. ESR signal saturation studies indicate a N acceptor spin–lattice relaxation time T1 (4.2 K) ≈ 3 × 10−4 s, notably different from the much smaller As a...

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Results are presented of recent studies in material exploration for W2W bonding and advanced W2W alignment carried out as a holistic approach to enable a robust ultra-fine pitch interconnect for 3Dsystem-on-chip (SoC) technology. Various characterization methods have been employed, including electron-spin-resonance (ESR) monitoring of dangling-bond-type defects, invoked to compare SiCN-SiCN and SiO 2 -SiO 2 bonding bonding strength in terms of the the evolution of chemical bond densities at the interface. Furthermore, sub-200 nm W2W overlay performance has been demonstrated to cope with 3D interconnect scaling and stringent contact requirements. State-of-the-art overlay performance is achieved by the enabling features of the W2W aligner while the incoming wafer characteristics are monitored. The study provides a positive outlook to 3D SoC technological realization and sub-µm pitch scaling solutions.

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Internal photoemission of electrons (IPE) from large area one monolayer 2H-MoS 2 films synthesized on top of amorphous (a−) SiO 2 or Al 2 O 3 is used to determine the energy of the semiconductor valence band (VB) relative to the reference level of the insulator conduction band (CB). This allows us to compare the VB top energy in MoS 2 to that of the (100)Si substrate crystal at the interface with the same insulator. Despite the CB in a–Al 2 O 3 is found to be ≈1 eV below that in SiO 2 as measured relative to the Si VB edge, the authors observe nearly no shift of the spectral threshold in the case of IPE from the MoS 2 VB. This observation indicates violation of electroneutrality at the MoS 2 /a–Al 2 O 3 interface causing an increase in barrier by ≈1 eV. This conclusion is supported by the much weaker field dependence of the IPE threshold at the MoS 2 /a–Al 2 O 3 interface compared to the MoS 2 /a–SiO 2 one, suggesting the presence of negative charges and/or interface dipoles. Therefore, the commonly accepted electron affinity rule (EAR) appears to be not appropriate to describe the band alignment at 2D/insulator interfaces. ispartof: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE vol:216 issue:8 ispartof: location:FRANCE, Strasbourg status: published

Silicene has so far been successfully grown on metallic substrates, like Ag(111), ZrB2(0001) and Ir(111) surfaces. However, the characterization of its electronic structure is hampered by the metallic substrate. In addition, potential applications of silicene in nanoelectronic devices will require its growth/integration with semiconducting or insulating substrates. In this chapter, we review recent theoretical works about the interaction of silicene with several non-metallic templates, distinguishing between the weak van der Waals like interaction of silicene with e.g. AlN or layered metal (di)chalcogenides, and the stronger covalent bonding between silicene and e.g. ZnS surfaces. Recent experimental results on the possible growth of silicene on MoS2 are also highlighted and compared to the theoretical predictions.

Thanks to its good thermal stability, including resistance to oxidation, platinum (Pt) is widely used in prototyping a wide spectrum of electron devices ranging from metal-oxide-semiconductor (MOS) transistors to resistive switching memory cells. In this work, the energy barriers for electrons between the Fermi level of Pt and the conduction band of several oxide insulators (SiO2, Al2O3, HfO2, Hf0.8Al0.2Ox, Sr0.53Ti0.47O3) were determined by using internal photoemission of electrons. By combining this barrier value with the electron affinity of the particular oxide, the effective work function (EWF) of Pt was determined for different interfaces. As studied over the reference Pt/oxide/Si stacks de-gassed in high vacuum at 400 °C, the EWF of Pt is found to differ significantly from the accepted vacuum WF value of 5.6 eV. The EWF is equal to 5.2 eV at the Pt/Al2O3 interface, 5.1 eV at Pt/HfO2, 5.3 eV at Pt/Hf0.8Al0.2Ox, 4.8 eV at Pt/SiO2, and 5.8 eV at the Pt/Sr0.53Ti0.47O3 interface indicating the presence of a polarization layer of which the contribution to the EWF depends on the oxide composition. Furthermore, annealing in H2 at 400 °C reduces the Pt EWF by ∼0.5 eV at all interfaces except for the Pt/Sr0.53Ti0.47O3 one. This observation indicates the formation of an additional H-related dipole at the Pt/oxide interfaces and suggests that the vacuum WF of Pt cannot be used as the value relevant for the MOS properties.

We have investigated fine grained polycrystalline silicon thin films grown by direct chemical vapor deposition on oxidized silicon substrates. More specifically, we analyze the influence of the doping type on the properties of this model polycrystalline silicon material. This includes an investigation of defect passivation and benchmarking of minority carrier properties. In our investigation, we use a variety of characterization techniques to probe the properties of the investigated polycrystalline silicon thin films, including Fourier Transform Photoelectron Spectroscopy, Electron Spin Resonance, Conductivity Activation, and Suns-Voc measurements. Amphoteric silicon dangling bond defects are identified as the most prominent defect type present in these layers. They are the primary recombination center in the relatively lowly doped polysilicon thin films at the heart of the current investigation. In contrast with the case of solar cells based on Czochralski silicon or multicrystalline silicon wafers, we conclude that no benefit is found to be associated with the use of n-type dopants over p-type dopants in the active absorber of the investigated polycrystalline silicon thin-film solar cells.

RF-sputtered thin films of spinel Li(x)Mg(1-2x)Al(2+x)O4 were investigated for use as solid electrolyte. The usage of this material can enable the fabrication of a lattice matched battery stack, which is predicted to lead to superior battery performance. Spinel Li(x)Mg(1-2x)Al(2+x)O4 thin films, with stoichiometry (x) ranging between 0 and 0.25, were formed after a crystallization anneal as shown by X-ray diffraction and transmission electron microscopy. The stoichiometry of the films was evaluated by elastic recoil detection and Rutherford backscattering and found to be slightly aluminum rich. The excellent electronic insulation properties were confirmed by both current-voltage measurements as well as by copper plating tests. The electrochemical stability window of the material was probed using cyclic voltammetry. Lithium plating and stripping was observed together with the formation of a Li-Pt alloy, indicating that Li-ions passed through the film. This observation contradicted with impedance measurements at open circuit potential, which showed no apparent Li-ion conductivity of the film. Impedance spectroscopy as a function of potential showed the occurrence of Li-ion intercalation into the Li(x)Mg(1-2x)Al(2+x)O4 layers. When incorporating Li-ions in the material the ionic conductivity can be increased by 3 orders of magnitude. Therefore it is anticipated that the response of Li(x)Mg(1-2x)Al(2+x)O4 is more adequate for a buffer layer than as the solid electrolyte.

The effective work function (EWF) and the energy position of the valence band in 20-40-nm thick VO2and V2O5layers grown by atomic layer deposition (ALD) on top of insulating SiO2 and γ-Al2O3 films were evaluated using the comparison between capacitance-voltage and internal photoemission measurements. From the capacitance measured at different temperatures on the metal-VO2(V2O5)-insulator-silicon and metal-insulator-silicon diodes we found that the both studied vanadium oxides have the same EWF as gold electrodes evaporated on the same oxides. This result is further collaborated by the internal photoemission experiments at the VO2/SiO2 and V2O5/SiO2 interfaces which indicate the energy barrier between the top of the vanadium oxide valence band (in the insulating phase) and the insulator conduction band to be 4.1 ± 0.1 eV. Since the transition from the narrow-gap VO2 to the wide-gap V2O5 oxide causes no change in the WF or in the photoemission threshold, we conclude that the ALD-grown VO2 in its insulating phase represents a a heavily-doped semiconductor which becomes metallic upon metal-insulator transition without significant EWF change. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work we analyse the influence of the O-scavenging process on interface traps in (100)Si/SiOx/HfO2(1.8 nm)/TiNx/Si stacks by using electrical measurements and electron spin resonance spectroscopy. The reduction of interfacial SiOx by high-temperature annealing in O-free ambient is found to lead to severe interface degradation exposed as generation of additional Si dangling bond defects (paramagnetic Pb0 centres). The density of these centres, well known to be electron traps impairing device operation, increases from ∼1 × 1012 cm−2 – the value typical for thermally oxidized Si – to >3 × 1012 cm−2 upon annealing at 1100 °C. This interface degradation is accompanied by the development of a hysteresis in the MOS capacitance–voltage curves indicating generation of additional oxide traps with areal density in the range of 1012 cm−2. However, the trap generation can be alleviated if the O-scavenging annealing step is performed in helium ambient, suggesting formation of silicon monoxide molecules at the Si/SiOx interface as the origin of the observed trap generation.

A low-temperature electron spin resonance study has been carried out on large-area high-purity polycrystalline two-dimensional few monolayer (ML) 2H MoS2 films synthesized by sulfurization of Mo layers, with intent to atomically assess mobility-degrading detrimental point defects. This reveals the presence of a distinct previously unreported anisotropic defect of axial symmetry about the c-axis characterized by g // = 2.00145 and g ⊥ = 2.0027, with corresponding density (spin S = ½) ~3 × 1012 cm−2 for a 4 ML thick film. Inverse correlation of the defect density with grain size points to a domain boundary associated defect, inherently incorporated during sample growth. Based on the analysis of ESR signal features in combination with literature data, the signal is tentatively ascribed to the a (di)sulfur antisite defect (S or S2 substituting for a Mo atom). Beset by these defects, the grain boundaries thus emerge as an intolerable threat for the carrier mobility and layer functionality.