scispace - formally typeset
Search or ask a question

Showing papers on "Band offset published in 2010"


Journal ArticleDOI
TL;DR: In this paper, the authors used density functional theory calculations with the HSE06 hybrid exchange-correlation functional to investigate InGaN alloys and accurately determine band gaps and band alignments.
Abstract: We use density functional theory calculations with the HSE06 hybrid exchange-correlation functional to investigate InGaN alloys and accurately determine band gaps and band alignments. We find a strong band-gap bowing at low In content. Band positions on an absolute energy scale are determined from surface calculations. The resulting GaN/InN valence-band offset is 0.62 eV. The dependence of InGaN valence-band alignment on In content is found to be almost linear. Based on the values of band gaps and band alignments, we conclude that InGaN fulfills the requirements for a photoelectrochemical electrode for In contents up to 50%.

320 citations


Journal ArticleDOI
TL;DR: InAs/GaSb nanowire heterostructures with thin GaInAs inserts were grown by MOVPE and characterized by electrical measurements and transmission electron microscopy, showing clear indications of band-to-band tunnelling.
Abstract: InAs/GaSb nanowire heterostructures with thin GaInAs inserts were grown by MOVPE and characterized by electrical measurements and transmission electron microscopy. Down-scaling of the insert thickness was limited because of an observed sensitivity of GaSb nanowire growth to the presence of In. By employing growth interrupts in between the InAs and GaInAs growth steps it was possible to reach an insert thickness down to 25 nm. Two-terminal devices show a diode behavior, where temperature-dependent measurements indicate a heterostructure barrier height of 0.5 eV, which is identified as the valence band offset between the InAs and GaSb. Three-terminal transistor structures with a top-gate positioned at the heterointerface show clear indications of band-to-band tunnelling.

174 citations


Journal ArticleDOI
TL;DR: In this paper, a combination of x-ray photoemission spectroscopy (XPS) and spectroscopic ellipsometry was used to measure the HfO2-Si valence and conduction band offsets (VBO and CBO) of both as-deposited and annealed stacks.
Abstract: The HfO2–Si valence and conduction band offsets (VBO and CBO, respectively) of technologically relevant HfO2/SiO2/Si film stacks have been measured by several methods, with several groups reporting values within a range of ∼1 eV for both quantities. In this study we have used a combination of x-ray photoemission spectroscopy (XPS) and spectroscopic ellipsometry to measure the HfO2–Si VBO and CBO of both as-deposited and annealed stacks. Unlike previous XPS based measurements of the HfO2–Si VBO, we have corrected for the effect of charging in the XPS measurement. We find that after correction for charging, the HfO2–Si VBOs are decreased from their typical XPS-measured values, and agree better with values measured by UV photoemission spectroscopy and internal photoemission. We also report values for the rarely reported HfO2–SiO2 and SiO2–Si VBOs and CBOs in HfO2/SiO2/Si stacks. In addition to the band offsets, XPS was used to measure the band bending in the Si substrate of HfO2/SiO2/Si film stacks. Unannealed HfO2 stacks showed downward Si band bending of 0.4–0.5 eV, while annealed HfO2 stacks showed negligible band bending. Finally, we investigated the composition of the SiO2 layer in SiO2/Si and HfO2/SiO2/Si. By decomposing the Si 2p spectra into the spin orbit partner lines of its five oxidation states we observed that the growth of the HfO2 films resulted in the growth of the SiO2 underlayer and an increase by a factor of ∼2.3 in the density of suboxide species of SiO2. Based on the relatively high binding energy of the Si 2p4+ level with respect to the Si 2p0 level and a survey of results from literature, we conclude that the SiO2 layer in the HfO2/SiO2/Si samples we measured does not undergo significant intermixing with HfO2.

112 citations


Journal ArticleDOI
TL;DR: Stoichiometric epitaxial LaAlO (3) grown on TiO(2)-terminated SrTiO(3)(001) by off-axis pulsed laser deposition is shown to exhibit strong cation intermixing, corroborated by classical and quantum mechanical calculations of the relative stabilities of abrupt and intermixed interface configurations.
Abstract: Stoichiometric epitaxial LaAlO(3) grown on TiO(2)-terminated SrTiO(3)(001) by off-axis pulsed laser deposition is shown to exhibit strong cation intermixing. This result is corroborated by classical and quantum mechanical calculations of the relative stabilities of abrupt and intermixed interface configurations. The valence band offset was measured to be 0.16 ± 0.10 eV, and this value cannot be accounted for theoretically without including intermixing in the physical description of the interface.

92 citations


Journal ArticleDOI
TL;DR: Control over the electronic structure of organic/inorganic semiconductor interfaces is required to realize hybrid structures with tailored opto-electronic properties and an approach towards this goal is demonstrated for a layered hybrid system composed of p-sexiphenyl and ZnO.
Abstract: Control over the electronic structure of organic/inorganic semiconductor interfaces is required to realize hybrid structures with tailored opto-electronic properties. An approach towards this goal is demonstrated for a layered hybrid system composed of p-sexiphenyl (6P) and ZnO. The molecular orientation can be switched from “upright-standing” to “flat-lying” by tuning the molecule–substrate interactions through aggregation on different crystal faces. The morphology change has profound consequences on the offsets between the molecular frontier energy levels and the semiconductor band edges. The combination of ZnO surface dipole modification through molecule adsorption and the orientation-dependence of the ionization energy of molecular layers shift these offsets by 0.7 eV. The implications for optimizing hybrid structures with regard to exciton and charge transfer are discussed.

60 citations


Journal ArticleDOI
TL;DR: In this article, the effects of Gd doping on band gap, band offset, oxygen vacancies, and electrical properties of amorphous HfO2 film have been studied.
Abstract: Effects of Gd doping on band gap, band offset, oxygen vacancies, and electrical properties of amorphous HfO2 film have been studied The results show that Gd incorporation helps increase band gap, conduction band offset and conduction band minimum, and reduce oxygen vacancies simultaneously Kept at the same physical thickness of 5 nm, Gd-doped HfO2 gate dielectric has a leakage current density of 90×10−4 A/cm2 at 1 V gate voltage, one and a half orders of magnitude lower than that of the pure HfO2 Gd doping also enhances the dielectric constant The capacitance equivalent thicknesses of 098 nm and 081 nm for HfO2 and Gd-doped HfO2 films, respectively, have been obtained

59 citations


Journal ArticleDOI
TL;DR: In this paper, the defect levels of surface dangling bonds and Au impurities in the Si shell were investigated and it was shown that dangling bond and substitutional Au defects behave as charge traps, generating hole carriers in the Ge core, while their defect levels are very deep in one component Si nanowires.
Abstract: The origin of the ballistic hole gas recently observed in Ge/Si core-shell nanowires has not been clearly resolved yet, although it is thought to be the result of the band offset at the radial interface. Here we perform spin-polarized density-functional calculations to investigate the defect levels of surface dangling bonds and Au impurities in the Si shell. Without any doping strategy, we find that Si dangling bond and substitutional Au defects behave as charge traps, generating hole carriers in the Ge core, while their defect levels are very deep in one-component Si nanowires. The defect levels lie to within 10 meV from or below the valence band edge for nanowires with diameters larger than 33 A and the Ge fractions above 30%. As carriers are spatially separated from charge traps, scattering is greatly suppressed, leading to the ballistic conduction, in good agreement with experiments.

43 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the detailed electrical-optical simulator ASDMP to model the measured output characteristics of heterojunction with intrinsic thin layer (HIT) cells on P- and N-type c-Si substrates.

35 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of nitrogen incorporation on the band alignment and electrical properties of HfTiO gate dielectric complementary metal-oxide-semiconductor (MOS) capacitors has been investigated by spectroscopy ellipsometry, x-ray photoelectron spectrograph, and electrical measurements.
Abstract: The effect of nitrogen incorporation on the band alignment and electrical properties of HfTiO gate dielectric complementary metal-oxide-semiconductor (MOS) capacitors has been investigated by spectroscopy ellipsometry, x-ray photoelectron spectroscopy, and electrical measurements. Reduction in optical band gap and band offsets has been detected. However, improved electrical properties have been achieved from HfTiON gate dielectric MOS capacitors attributed to the nitrogen-induced reduction in oxygen-related traps and the improved interface quality. Although there is a nitrogen-induced reduction in band gap and band offset, the sufficient barrier heights still makes HfTiON a promising high-k gate dielectric candidate for proposed near-future complementary metal-oxide-semiconductor applications.

32 citations


Journal ArticleDOI
TL;DR: The calculations show that the conduction band offset of InAs(1-x)Sb(x)/GaAs can be continuously tuned from 0 to 500 meV and a flat conductionBand alignment exists when 60% Sb is incorporated into the QDs.
Abstract: We report the growth of InAs1−xSbx self-assembled quantum dots (QDs) on GaAs (100) by molecular beam epitaxy. The optical properties of the QDs are investigated by photoluminescence (PL) and time-r...

29 citations


Journal ArticleDOI
TL;DR: Combined cross-sectional scanning tunneling microscopy and spectroscopy results reveal the interplay between the atomic structure of ring-shaped GaSb quantum dots in GaAs and the corresponding electronic properties.
Abstract: Combined cross-sectional scanning tunneling microscopy and spectroscopy results reveal the interplay between the atomic structure of ring-shaped GaSb quantum dots in GaAs and the corresponding electronic properties. Hole confinement energies between 0.2 and 0.3 eV and a type-II conduction band offset of 0.1 eV are directly obtained from the data. Additionally, the hole occupancy of quantum dot states and spatially separated Coulomb-bound electron states are observed in the tunneling spectra.

Journal ArticleDOI
TL;DR: In this paper, low-frequency noise has been studied in compressively strained Si0.8Ge0.2 core-shell nanowire (NW) p-channel transistors compared with unstrained NWs.
Abstract: Low-frequency noise has been studied in compressively strained Si0.8Ge0.2 core-shell nanowire (NW) p-channel transistors compared with unstrained NWs. The noise has been well interpreted using the carrier number with correlated mobility fluctuation model. The volume trap density, Nt, lies in the range of 2.9×1018–4.3×1019 cm−3 eV−1, which is similar to standard high-k planar devices. The impact of Coulomb and surface roughness scatterings is more significant in unstrained SiGe NWs. This result can be explained by the better carrier confinement at the central region of SiGe NWs due to the additional band offset in the compressively strained NWs.

Journal ArticleDOI
TL;DR: In this paper, the influence of band bending and polarization on the valence band offset measured by x-ray photoelectron spectroscopy (XPS) is discussed, and a modification method based on a modified self-consistent calculation is proposed to eliminate the influence and thus increasing the precision of XPS.
Abstract: The influence of band bending and polarization on the valence band offset measured by x-ray photoelectron spectroscopy (XPS) is discussed, and a modification method based on a modified self-consistent calculation is proposed to eliminate the influence and thus increasing the precision of XPS. Considering the spontaneous polarization at the surfaces and interfaces and the different positions of Fermi levels at the surfaces, we compare the energy band structures of Al/Ga-polar AlN/GaN and N-polar GaN/AlN heterojunctions, and give corrections to the XPS-measured valence band offsets. Other AlN/GaN heterojunctions and the piezoelectric polarization are also introduced and discussed in this paper.

Journal ArticleDOI
TL;DR: In this paper, the structural, electronic, optical and thermodynamic properties of quaternary alloys were investigated using the full potential-linearized augmented plane wave plus local orbitals method within the density functional theory.

Journal ArticleDOI
TL;DR: In this article, X-ray photoelectron spectroscopy was employed to study the valence band discontinuity and interface formation in the ZnO/6H-SiC heterojunction.


Journal ArticleDOI
TL;DR: In this article, the authors measured the valence band offset (VBO) of MgO/TiO2 (rutile) heterojunction by X-ray photoelectron spectroscopy.

Journal ArticleDOI
TL;DR: In this article, the authors introduce a theoretical scheme to study defect energy levels and band alignments at semiconductor-oxide interfaces, which relies on hybrid functionals to overcome the band gap underestimation typically achieved with semilocal density functionals.
Abstract: We introduce a theoretical scheme to study defect energy levels and band alignments at semiconductor-oxide interfaces. The scheme relies on hybrid functionals to overcome the band gap underestimation typically achieved with semilocal density functionals. For atomically localized defects, the more accurate description achieved with, hybrid functionals does not lead to significant shifts of the charge transition levels, provided these levels are referred to a common reference potential. This result effectively decouples the shifts of the band edges with respect to the defect levels. We also show that relative shifts of conduction and valence band edges as determined by exact nonlocal exchange. lead to band offsets in excellent agreement with experimental values for several semiconductor-oxide interfaces. The proposed scheme is illustrated through a series of applications, including the dangling bond defects in silicon and germanium, the charge state of the O-2 molecule during silicon oxidation, and the oxygen vacancy in Si-SiO2 HfO2 stacks. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal ArticleDOI
TL;DR: In this paper, all electron full potential calculations based on spin density functional theory were performed to study cubic zincblende (ZB) and hexagonal NiAs structures of bulk CrTe, free (0, 0, 1) surfaces of ZB CrTe and interface of CrTe with ZnTe, and the obtained phase diagram evidences more stability of the Te terminated surface compared with the Cr termination.

Journal ArticleDOI
TL;DR: In this paper, the authors measured Al 2p spectra and determined the atomic species that terminated the interface between the alumina films and the substrates, based on thermodynamics.

Journal ArticleDOI
TL;DR: X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) of the w-InN/h-BN heterojunction and it is found that it is a type-IIheterojunction with the VBO being −0.30 ± 0.09 eV.
Abstract: X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) of the w-InN/h-BN heterojunction. We find that it is a type-II heterojunction with the VBO being −0.30 ± 0.09 eV and the corresponding conduction band offset (CBO) being 4.99 ± 0.09 eV. The accurate determination of VBO and CBO is important for designing the w-InN/h-BN-based electronic devices.

Journal ArticleDOI
TL;DR: In this paper, the energy band gap, alignment with Si and the chemical bonding of 3-4 nm thick HfxSi1−xO2 films with 0≤x≤1 were investigated as a function of composition.
Abstract: The energy band gap, alignment with Si and the chemical bonding of 3–4 nm thick HfxSi1−xO2 films with 0≤x≤1 were investigated as a function of composition. Nitrogen was introduced by N plasma incorporation into HfxSi1−xO2 films with x=0.3, 0.5, and 0.7 grown on a SiO2/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 SiO2) to a value of 5.3 eV (for pure HfO2). 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 SiO2) to a value of 1...

Journal ArticleDOI
TL;DR: In this article, the interface structure and band alignments of various dielectric/GaAs structures have been investigated systematically, and the results indicate that ALD HfO2/Al2O3 nanolaminate structures could effectively tune the interface quality and band offset of gate Dielectric films on n-GaAs.
Abstract: HfO2, Al2O3 and HfO2/Al2O3 (AHO) nanolaminates with various Al/Hf ratios (including 1:3.0, 1:2.1 and 1:1.3) were fabricated on S-passivated GaAs substrates by atomic layer deposition (ALD). The interface structure and band alignments of various dielectric/GaAs structures have been investigated systematically. The AHO films with the Al/Hf ratio of 1:1.3 suppress the formation of As oxides and elemental As overlayers around AHO/GaAs interfaces more effectively than other samples, showing higher accumulation capacitance, less hysteresis width (ΔVFB = 415 mV) and lower leakage current density. The band alignments of interfaces of HfO2/GaAs, Al2O3/GaAs and AHO/GaAs were established. The results indicate that ALD HfO2/Al2O3 nanolaminate structures could effectively tune the interface quality and band offset of gate dielectric films on n-GaAs.

Journal ArticleDOI
TL;DR: In this paper, first-principles DFT simulations provide strong evidence that, at zero temperature, for SiGe oriented SiGe nanowires (NWs), the segregated structure is preferable with respect to the mixed ones; for this observation two different schemes of calculations are presented and discussed.
Abstract: Results of first-principles DFT simulations provide strong evidence that, at zero temperature, for [110] oriented SiGe nanowires (NWs), the segregated structure is favoured with respect to the mixed ones; for this observation two different schemes of calculations are presented and discussed. Moreover the segregation strongly influences the NWs electronic properties, inducing a reduced quantum confined effect (RQCE). We show here that it depends on the effect of strain in the plane normal to the direction of growth and not on the choice of lattice parameter in the direction of growth. A qualitative evaluation of the band offset between Si and Ge for SiGe NWs is also presented.

Journal ArticleDOI
TL;DR: In this paper, the authors report the studies of atomic and electronic structures at ZnO and ZrO 2 interface using high-resolution transmission electron microscopy (TEM).
Abstract: In this paper, we report the studies of atomic and electronic structures at ZnO and ZrO 2 interface. The epitaxial heterostructures were grown by laser molecular beam epitaxy and the interface atomic structure was determined by using high-resolution transmission electron microscopy (TEM). Band alignment for high-k ZrO 2 layer on ZnO was investigated by in situ X-ray photoemission spectroscopy (XPS) characterization and first-principles calculations based on density functional theory (DFT). The valence and conduction band offsets (CBOs) were found to be 0.27 ± 0.05 eV and 2.16 ± 0.05 eV, respectively. The results are in good agreement with values from theoretical calculations. The large CBO and small lattice mismatch between ZnO and ZrO 2 suggest potential for ZrO 2 to be used as a gate dielectric in ZnO-based transparent electronic devices.

Journal ArticleDOI
TL;DR: X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band offset (VBO) of InN/diamond heterostructure and the value of VBO was determined to be 0.39 ± 0.08 eV.
Abstract: Diamond is not only a free standing highly transparent window but also a promising carrier confinement layer for InN based devices, yet little is known of the band offsets in InN/diamond system. X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band offset (VBO) of InN/diamond heterostructure. The value of VBO was determined to be 0.39 ± 0.08 eV and a type-I heterojunction with a conduction band offset (CBO) of 4.42 ± 0.08 eV was obtained. The accurate determination of VBO and CBO is important for the application of III-N alloys based electronic devices.

Journal ArticleDOI
TL;DR: In this paper, the position of the valence-band maximum was determined by convolving theoretically calculated density of states from first-principles calculations and comparing with experimental valence band data.
Abstract: Hard x-ray photoelectron spectroscopy has been used to study the band alignment between atomic layer deposited HfO2 on clean Ge (100) and nitrogen treated Ge (100) surfaces. The position of the valence-band maximum was determined by convolving theoretically calculated density of states from first-principles calculations and comparing with experimental valence-band data. Using Kraut’s method, the valence-band offsets were found to be 3.2±0.1 and 3.3±0.1 eV for the samples grown on clean and N passivated Ge, respectively. The oxide charge measured from capacitance-voltage measurements shows a significant increase between the two samples; however, the small change in the band offset between the two systems strongly indicates negligible contribution of the interface to the conduction/valence-band barrier and the band alignment of the heterojunctions.

Journal ArticleDOI
TL;DR: In this paper, both epitaxial and amorphous ultra-thin alumina films were grown on a Cu-9 at.%Al(1 1 1) substrate by selective oxidation of Al in the alloy in ultra high vacuum.

Journal ArticleDOI
TL;DR: In this article, the valence band offset (VBO) of w -ZnO(101)/bcc-In2O3(111) heterojunction was measured to settle the question of the band line-up of the ZnO/ In2O 3 heterojoint.

Journal ArticleDOI
TL;DR: In this paper, the authors provided a systematic investigation of the band alignment of quinary GaInNAsSb alloy based quantum wells, starting from the simplest ternary GaInAs compound to the new quinary quinary InNAs Sb one, which shows a good electron confinement resulting in a high characteristic temperature.
Abstract: In this paper, we provide a systematic investigation of the band alignment of quinary GaInNAsSb alloy based quantum wells, starting from the simplest ternary GaInAs compound to the new quinary GaInNAsSb one. We calculate the band gap and the band discontinuities of Ga 1− x In x N y As 1− y − z Sb z structures, using band anticrossing (BAC) models applied simultaneously to conduction and valence band. Nitrogen and antimony concentrations leading to an emission wavelength of 1.6 μm have been determined ( x =38%, y =2%, z =4%). This structure shows a good electron confinement resulting in a high characteristic temperature. GaInNAsSb has been found to be a potentially superior material to both InGaAsP and GaInNAs for communication wavelength laser applications.