Showing papers on "Band offset published in 2013"
TL;DR: In this paper, the band offsets and heterostructures of monolayer and few-layer transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te) are investigated from first principles calculations.
Abstract: The band offsets and heterostructures of monolayer and few-layer transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te) are investigated from first principles calculations. The band alignments between different MX2 monolayers are calculated using the vacuum level as reference, and a simple model is proposed to explain the observed chemical trends. Some of the monolayers and their heterostructures show band alignments suitable for potential applications in spontaneous water splitting, photovoltaics, and optoelectronics. The strong dependence of the band offset on the number of layers also implicates a possible way of patterning quantum structures with thickness engineering.
1,422 citations
TL;DR: In this paper, the authors show that the band gap of three-dimensional hybrid perovskites is dominated by a giant spin-orbit coupling (SOC) in the conduction-band (CB).
Abstract: Three-dimensional (3D) hybrid perovskites CH3NH3PbX3 (X = Br, I) have recently been suggested as new key materials for dye-sensitized solar cells (DSSC) leading to a new class of hybrid semiconductor photovoltaic cells (HSPC). Thanks to density functional theory calculations, we show that the band gap of these compounds is dominated by a giant spin–orbit coupling (SOC) in the conduction-band (CB). At room temperature, direct and isotropic optical transitions are associated to a spin–orbit split-off band related to the triply degenerated CB of the cubic lattice without SOC. Due to the strong SOC, the electronic states involved in the optical absorption are only slightly perturbed by local distortions of the lattice. In addition, band offset calculations confirm that CH3NH3PbX3/TiO2 is a reference material for driving electrons toward the electrode in HSPC. Two-dimensional (2D) hybrids are also suggested to reach further flexibility for light conversion efficiency. Our study affords the basic concepts to re...
1,027 citations
TL;DR: It is demonstrated that rational design and construction of isotype heterojunction could open up a new avenue for the development of new efficient visible-light photocatalysts and the removal of NO in air.
Abstract: The photocatalytic performance of the star photocatalyst g-C3N4 was restricted by the low efficiency because of the fast charge recombination. The present work developed a facile in situ method to construct g-C3N4/g-C3N4 metal-free isotype heterojunction with molecular composite precursors with the aim to greatly promote the charge separation. Considering the fact that g-C3N4 samples prepared from urea and thiourea separately have different band structure, the molecular composite precursors of urea and thiourea were treated simultaneously under the same thermal conditions, in situ creating a novel layered g-C3N4/g-C3N4 metal-free heterojunction (g-g CN heterojunction). This synthesis method is facile, economic, and environmentally benign using easily available earth-abundant green precursors. The confirmation of isotype g-g CN heterojunction was based on XRD, HRTEM, valence band XPS, ns-level PL, photocurrent, and EIS measurement. Upon visible-light irradiation, the photogenerated electrons transfer from ...
1,024 citations
TL;DR: In this paper, the authors performed hybrid functional calculations of native point defects and dangling bonds (DBs) in α-Al2O3 to aid in the identification of charge-trap and fixed-charge centers in Al 2O3/III-V metaloxide-semiconductor structures.
Abstract: We performed hybrid functional calculations of native point defects and dangling bonds (DBs) in α-Al2O3 to aid in the identification of charge-trap and fixed-charge centers in Al2O3/III-V metal-oxide-semiconductor structures. We find that Al vacancies (VAl) are deep acceptors with transition levels less than 2.6 eV above the valence band, whereas Al interstitials (Ali) are deep donors with transition levels within ∼2 eV of the conduction band. Oxygen vacancies (VO) introduce donor levels near midgap and an acceptor level at ∼1 eV below the conduction band, while oxygen interstitials (Oi) are deep acceptors, with a transition level near the mid gap. Taking into account the band offset between α-Al2O3 and III-V semiconductors, our results indicate that VO and Al DBs act as charge traps (possibly causing carrier leakage), while VAl, Ali, Oi, and O DBs act as fixed-charge centers in α-Al2O3/III-V metal-oxide-semiconductor structures.
201 citations
TL;DR: The impact of post-deposition hydrogen plasma treatment (HPT) on passivation in amorphous/crystalline silicon (a-Si:H/c-Si) interfaces is investigated in this paper.
Abstract: The impact of post-deposition hydrogen plasma treatment (HPT) on passivation in amorphous/crystalline silicon (a-Si:H/c-Si) interfaces is investigated. Combining low temperature a-Si:H deposition and successive HPT, a high minority carrier lifetime >8 ms is achieved on c-Si 〈100〉, which is otherwise prone to epitaxial growth and thus inferior passivation. It is shown that the passivation improvement stems from diffusion of hydrogen atoms to the heterointerface and subsequent dangling bond passivation. Concomitantly, the a-Si:H hydrogen density increases, leading to band gap widening and void formation, while the film disorder is not increased. Thus, HPT allows for a-Si:H band gap and a-Si:H/c-Si band offset engineering.
136 citations
TL;DR: Examination of CdSe/CdS dot-in-rod NRs, a representative of 1D heterostructures, and DIR-electron-acceptor complexes by transient absorption spectroscopy shows that excitation into the CdS rod forms three distinct types of long-lived excitons that are spatially localized in the CDS rod, in and near the C dSe seed and in the cdS shell surrounding the seed.
Abstract: Colloidal one-dimensional semiconductor nanoheterostructures have emerged as an important family of functional materials for solar energy conversion, although the nature of the long-lived exciton state and their formation and dissociation dynamics remain poorly understood. In this paper we study these dynamics in CdSe/CdS dot-in-rod (DIR) NRs, a representative of 1D heterostructures, and DIR-electron-acceptor complexes by transient absorption spectroscopy. Because of a quasi-type II band alignment of CdSe and CdS, it is often assumed that there exists one long-lived exciton state with holes localized in the CdSe seed and electrons delocalized among CdSe and CdS. We show that excitation into the CdS rod forms three distinct types of long-lived excitons that are spatially localized in the CdS rod, in and near the CdSe seed and in the CdS shell surrounding the seed. The branching ratio of forming these exciton states is controlled by the competition between the band offset driven hole localization to the CdS...
92 citations
TL;DR: In this article, the interface region between Ga-face n-type GaN and Al2O3 dielectric was investigated by X-ray photoelectron spectroscopy (XPS), and an increase in the Ga-O to Ga-N bond intensity ratio following Al 2O3 deposition implies that the growth of an interfacial gallium suboxide (GaOx) layer occurred during the ALD process.
Abstract: The interface region between Ga-face n-type GaN and Al2O3 dielectric (achieved via atomic-layer deposition or ALD) is investigated by X-ray photoelectron spectroscopy (XPS). An increase in the Ga-O to Ga-N bond intensity ratio following Al2O3 deposition implies that the growth of an interfacial gallium sub-oxide (GaOx) layer occurred during the ALD process. This finding may be ascribed to GaN oxidation, which may still happen following the reduction of a thin native GaOx by trimethylaluminum (TMA) in the initial TMA-only cycles. The valence band offset between GaN and Al2O3, obtained using both core-level and valence band spectra, is found to vary with the thickness of the deposited Al2O3. This observation may be explained by an upward energy band bending at the GaN surface (due to the spontaneous polarization induced negative bound charge on the Ga-face GaN) and the intrinsic limitation of the XPS method for band offset determination.
61 citations
TL;DR: In this article, the authors measured the valence band offset at the interface between CdS and Cu2ZnSnS4 using hard X-ray photoelectron spectroscopy (HAXPES).
Abstract: We directly and non-destructively measured the valence band offset at the interface between CdS and Cu2ZnSnS4 (CZTS) using hard X-ray photoelectron spectroscopy (HAXPES), which can measure the electron state of the buried interface because of its large analysis depth. These measurements were made using the following real devices; CZTS(t = 700 nm), CdS(t = 100 nm)/CZTS(t = 700 nm), and CdS(t = 5 nm)/CZTS(t = 700 nm) films formed on Mo coated glass. The valence band spectra were measured by HAXPES using an X-ray photon energy of 8 keV. The value of the valence band offset at the interface between CdS and CZTS was estimated as 1.0 eV by fitting the spectra. The conduction band offset could be deduced as 0.0 eV from the obtained valence band offset and the band gap energies of CdS and CZTS.
52 citations
TL;DR: In this paper, the conduction and valence band offsets at the CdS/Cu2ZnSnSe4 interface were studied by X-ray photoemission spectroscopy.
Abstract: Band alignment at CdS/Cu2ZnSnSe4 heterojunction interface is studied by X-ray photoemission spectroscopy. The Cu2ZnSnSe4 thin films are prepared by selenization of electrodeposited Cu-Zn-Sn precursors. CdS overlayers with different thickness are sequentially grown on the Cu2ZnSnSe4 substrate by pulsed laser deposition process. Photoemission spectra are obtained before and after each growth to study the conduction and valence band offsets at the heterojunction interface. The determined conduction band offset of 0.34 eV indicates a spike-like ‘type I’ band alignment at CdS/Cu2ZnSnSe4 interface. The spike will avoid interface recombination, and it is low enough that electron could transfer from the Cu2ZnSnSe4 layer to the buffer layer which is suitable for solar cell's fabrication. Copyright © 2012 John Wiley & Sons, Ltd.
47 citations
TL;DR: Because of the staggered band offset which promoted effective charge separation, the as-synthesized ZnSe-ZnO NRs exhibited remarkable photocatalytic activities under visible light illumination, demonstrating their promising potentials in relevant photoconversion applications.
Abstract: A novel one-step cation exchange approach has been developed to prepare ZnO-decorated ZnSe nanorods (ZnSe–ZnO NRs), a prototype type-II semiconductor nanoheterostructure. Because of the staggered band offset which promoted effective charge separation, the as-synthesized ZnSe–ZnO NRs exhibited remarkable photocatalytic activities under visible light illumination, demonstrating their promising potentials in relevant photoconversion applications.
46 citations
TL;DR: In this article, a set of LaAlO3/SrTiO3 interfaces has been probed by x-ray photoemission spectroscopy in order to contrast and compare the effects of LAO overlayer thickness and of the growth conditions on the electronic properties of these heterostructures.
Abstract: A set of LaAlO3/SrTiO3 (LAO-STO) interfaces has been probed by x-ray photoemission spectroscopy in order to contrast and compare the effects of LAO overlayer thickness and of the growth conditions on the electronic properties of these heterostructures. These effects are tracked by considering the band offset and the density of Ti+3 states, respectively. It is shown that the dominant effects on the local electronic properties are determined by the O2 partial pressure during the growth. In particular, a low PO2 yields Ti+3 states with higher density and lower binding energy compared to the sample grown at high PO2 or to the bare STO reference sample. Band-offset effects are all below about 0.7 eV, but a careful analysis of Ti 2p and Sr 3d peaks shows that valence-band offsets can be at the origin of the observed peak width. In particular, the largest offset is shown by the conducting sample, which displays the largest Ti 2p and Sr 3d peak widths
TL;DR: In this article, the authors applied the coherent potential approach to handle the configuration average of Al doping and a recently proposed semi-local exchange potential to accurately determine the band gaps of the materials.
Abstract: Using an atomistic first principles approach, we investigate the band offset of the GaAs/AlxGa1−xAs heterojunctions for the entire range of the Al doping concentration 0
TL;DR: In this article, the impact of ZnO layer thickness on optical and resistive switching behavior of BaTiO3/ZnO heterostructures grown by pulsed laser deposition is reported.
Abstract: This work reports the impact of ZnO layer thickness on optical and resistive switching behavior of BaTiO3/ZnO heterostructures grown by pulsed laser deposition. The interface polarization coupling becomes more efficient and causes a remarkable change in heterostructure properties with decrease in ZnO layer thickness. The heterostructure with ZnO thickness of 25 nm displays the enhanced resistive switching characteristics with switching ratio ≈106 and good stability in low and high resistance states. Moreover, the photoluminescence spectrum exhibits two additional blue emissions when ZnO thickness is ≤50 nm and their mechanism is highlighted based on interface band offset and interface polarization coupling effect.
TL;DR: In this article, the authors investigated the valence band offsets of the CuInSe${}_{2}$/CdS and CuInS${}{2]$/ZnS (110) interfaces based on various definitions using first-principles calculations in the framework of hybrid density functional theory.
Abstract: The valence band offsets of the CuInSe${}_{2}$/CdS and CuInSe${}_{2}$/ZnS (110) interfaces are obtained based on various definitions using first-principles calculations in the framework of hybrid density functional theory. Both the strained band offset and the unstrained, or natural, band offset are investigated, where the two phases share and do not share in-plane lattice parameters perpendicular to the stacking direction, respectively. The valence band offset is determined by first obtaining the difference between the reference levels of two phases in the regions far from the interface and then adding the difference between the valence band maximum and the reference levels of bulk for the two phases. The nonfaceted (110) interface and a number of (112)/(11$\overline{2}$) faceted interfaces, some containing ordered point defects in the CuInSe${}_{2}$ (CIS) region, are considered. The excess energies of CIS/CdS and CIS/ZnS interfaces are lower when there are no ordered point defects, in contrast to the CIS surfaces that stabilize with ordered defect formation. The valence band offset is not significantly dependent on the atomic configurations at the interface as long as there are no charged layers. Surface calculations suggest that the reference level, which is determined by the average electrostatic potential at the atomic site, is not strongly dependent on lattice strain. A definition of the natural valence band offset that assumes a strain-invariant difference in the reference levels of the two phases provides values almost independent of the in-plane lattice parameters used in the interface calculation, which are about $\ensuremath{-}$1.2 and $\ensuremath{-}$1.3 eV with respect to CIS for the CIS/CdS and CIS/ZnS interfaces that contain no charged layers, respectively. The ionization potential difference can differ from the natural valence band offset by up to 0.3 eV without any consistent tendency to overestimate or underestimate, showing that the ionization potential difference is not necessarily a reasonable measure of the natural valence band offset.
TL;DR: In this article, structural, morphological, and band offset properties of GaAs/Ge/GaAs heterostructures grown in situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers, connected via vacuum transfer chamber, were investigated.
Abstract: Structural, morphological, and band offset properties of GaAs/Ge/GaAs heterostructures grown in situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers, connected via vacuum transfer chamber, were investigated. Reflection high energy electron diffraction (RHEED) studies in all cases exhibited a streaky reconstructed surface pattern for Ge. Sharp RHEED patterns from the surface of GaAs on epitaxial Ge/(111)A GaAs and Ge/(110)GaAs demonstrated a superior interface quality than on Ge/(100)GaAs. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of Ge about 0.2–0.3 nm. High-resolution triple axis x-ray rocking curves demonstrate a high-quality Ge epitaxial layer as well as GaAs/Ge/GaAs heterostructures by observing Pendellosung oscillations. Valence band offset, ΔEv, have been derived from x-ray photoelectron spectroscopy (XPS) data on GaAs/Ge/GaAs interfaces for three crystallographic orientations. The ΔEv values for epitaxial GaAs...
TL;DR: In this article, advanced first-principles calculations were used to predict that the non-polar SrTiO$_3$/SrZrO$-3$ (001) interface of a superlattice can host a 2-dimensionally confined electron gas.
Abstract: Using advanced first-principles calculations we predict that the non-polar SrTiO$_3$/SrZrO$_3$ (001) interface, designed as either thin SrZrO$_3$ film deposited on SrTiO$_3$ or short-period (SrTiO$_3$)$_m$/(SrZrO$_3$)$_n$ superlattice, host a 2-dimensionally confined electron gas. Mobile electron charge due to native impurities, field-effect, or modulation doping remains tightly trapped at the interface. Key ingredients for this occurrence are a) the peculiar chemistry of 3d orbitals, b) the large band offset at titanate-zirconate interface.
TL;DR: In this article, a band diagram based on the conventional band bending picture is proposed to explain the evolution of the apparent barrier height from electrical measurements and it suggests that the work function of VO2 decreases by ∼ 0.2 µV when it goes through the insulator to metal transtion, in qualitative agreement with Kelvin force microscopy measurements reported in literature.
Abstract: We report on experimental realization of p-n heterojunctions based on p-type GaN, and an n-type correlated oxide, VO2. The band offsets are evaluated by current-voltage and capacitance-voltage measurements at various temperatures. A band diagram based on the conventional band bending picture is proposed to explain the evolution of the apparent barrier height from electrical measurements and it suggests that the work function of VO2 decreases by ∼0.2 eV when it goes through the insulator to metal transtion, in qualitative agreement with Kelvin force microscopy measurements reported in literature. The frequency-dependent capacitance measurements allow us to differentiate the miniority carrier effect from the interface states and series resistance contributions, and estimate the minority carrier lifetime in insulating phase of VO2 to be of the order of few microseconds. The nitride-oxide based p-n heterojunctions provide a new dimension to study correlated-electron systems and could be of relevance to emerging electronic devices that exploit collective phenomena.
TL;DR: In this paper, a band diagram based on the conventional band bending picture is proposed to explain the evolution of the apparent barier height from electrical measurements and it suggests that the work function of VO2 decreases by 0.2 eV when it goes through the insulator to metal transtion, in qualitative agreement with Kelvin force microscopy measurements reported in literature.
Abstract: We report on experimental realization of p-n heterojunctions based on p-type GaN, and an n-type correlated oxide, VO2. The band offsets are evaluated by current-voltage and capacitance voltage measurements at various temperatures. A band diagram based on the conventional band bending picture is proposed to explain the evolution of the apparent barier height from electrical measurements and it suggests that the work function of VO2 decreases by ~0.2 eV when it goes through the insulator to metal transtion, in qualitative agreement with Kelvin force microscopy measurements reported in literature. The frequency dependent capacitance measurements allows us to differentiate the miniority carrier effect from the interface states and series resistance contributions, and estimate the minority carrier lifetime in insulating phase of VO2 to be of the order of few microseconds. The nitride-oxide based p-n heterojunctions provide a new dimension
TL;DR: In this article, an effective increase in the Seebeck coefficient for 5% La-doped SrTiO 3 nanoceramics at temperatures of 300-800 K through grain boundary doping with Nb, which results in an improvement of power factor by a value as high as 35%.
01 Jan 2013
TL;DR: In this article, the electrostatic integrity of 7 nm-node bulk FinFETs was studied and it was shown that the electrostatics of bulk-FF match those of SOI-and GeOI-FF for the 7 nm node.
Abstract: The electrostatic integrity of 7 nm-node bulk FinFETs (FF) is studied by TCAD. Lowly-doped bulk-FF have worse electrostatics than SOI- and GeOI-FF. However, by introducing a 200 meV band offset/quantum barrier (QB) under the channel or a > 1e18 doped ground-plane (GP), the electrostatics of bulk-FF match those of SOI-and GeOI-FF for the 7 nm-node. For sufficient substrate isolation, the band offset must be positioned within 5 nm of the STI edge. The QB layer that provides the offset can be thinned down to 10 nm. A GP is more robust to variations in position, but thinning this layer requires doping levels that are undesired especially for Ge. Bulk-FF with GP or QB isolation show good scalability to the 5 nm-node, improving both IEFF and DIBL.
TL;DR: In this paper, the roles of Fermi level of doped a-Si:H and band offsets at the aSi-H/c-Si interface were studied through computer simulation.
TL;DR: In this paper, a heterojunction photodiode was fabricated from multiwalled carbon nanotubes (MWCNTs)/ZnO nanowires/p-Si (100) substrate composite structure.
Abstract: A heterojunction photodiode was fabricated from multiwalled carbon nanotubes (MWCNTs)/ZnO nanowires/p-Si (100) substrate composite structure. The heterojunction photodiode demonstrated a faster transient response and higher responsivity than the reference sample without deposition of MWCNTs, which is attributed to improved carrier collection and transport efficiency through the MWCNTs network. The high photoresponsivities of the devices are explained in terms of operation as a hybrid of photodiode and photoconductor modes. The spectral response of the devices showed dependence on voltage polarity and is attributed to the high valance band offset in the interfacial region of ZnO and p-Si substrate.
TL;DR: In this article, photoemission and cathodoluminescence techniques were used to measure formation of the BaTiO3 (BTO) on SrTiO 3 (STO) heterojunction band offset grown monolayer by monoline by molecular beam epitaxy.
Abstract: We used a complement of photoemission and cathodoluminescence techniques to measure formation of the BaTiO3 (BTO) on SrTiO3 (STO) heterojunction band offset grown monolayer by monolayer by molecular beam epitaxy. X-ray photoemission spectroscopy (XPS) provided core level and valence band edge energies to monitor the valence band offset in-situ as the first few crystalline BTO monolayers formed on the STO substrate. Ultraviolet photoemission spectroscopy (UPS) measured Fermi level positions within the band gap, work functions, and ionization potentials of the growing BTO film. Depth-resolved cathodoluminescence spectroscopy measured energies and densities of interface states at the buried heterojunction. Kraut-based XPS heterojunction band offsets provided evidence for STO/BTO heterojunction linearity, i.e., commutativity and transitivity. In contrast, UPS and XPS revealed a large dipole associated either with local charge transfer or strain-induced polarization within the BTO epilayer.
TL;DR: In this paper, the experimental study of the valence band offset (ΔEv) of a mixed As/Sb type-II staggered gap GaAs0.35Sb0.7Ga0.3As heterostructure used as source/channel junction of n-channel tunnel field effect transistor (TFET) grown by molecular beam epitaxy was investigated by x-ray photoelectron spectroscopy (XPS).
Abstract: The experimental study of the valence band offset (ΔEv) of a mixed As/Sb type-II staggered gap GaAs0.35Sb0.65/In0.7Ga0.3As heterostructure used as source/channel junction of n-channel tunnel field effect transistor (TFET) grown by molecular beam epitaxy was investigated by x-ray photoelectron spectroscopy (XPS). Cross-sectional transmission electron micrograph shows high crystalline quality at the source/channel heterointerface. XPS results demonstrate a ΔEv of 0.39 ± 0.05 eV at the GaAs0.35Sb0.65/In0.7Ga0.3As heterointerface. The conduction band offset was calculated to be ∼0.49 eV using the band gap values of source and channel materials and the measured valence band offset. An effective tunneling barrier height of 0.21 eV was extracted, suggesting a great promise for designing a metamorphic mixed As/Sb type-II staggered gap TFET device structure for low-power logic applications.
29 Nov 2013
TL;DR: In this article, double transparent conductive oxide (TCO) film-embedded Si heterojunction solar cells were fabricated and three different TCO coatings were formed by sputtering method for an Al-doped ZnO (AZO), an indium-tin-oxide (ITO) and double stacks of ITO/AZO films.
Abstract: Double transparent conductive oxide (TCO) film-embedded Si heterojunction solar cells were fabricated. An intentional doping was not applied for heterojunction solar cells due to the spontaneous Schottky junction formation between TCO films and an n-type Si substrate. Three different TCO coatings were formed by sputtering method for an Al-doped ZnO (AZO) film, an indium-tin-oxide (ITO) film and double stacks of ITO/AZO films. An improved crystalline ITO film was grown on an AZO template upon hetero-epitaxial growth. This double TCO films-embedded Si (ITO/AZO/Si) heterojunction solar cell provided significantly enhanced efficiency of 9.23 % as compared to the single TCO/Si (ITO/Si or AZO/Si) devices due to the optical and the electrical benefits. The effective arrangement of TCO films (ITO/AZO) provides benefits of a lower front contact resistance and a smaller band offset to Si leading enhanced photovoltaic performances. This demonstrates a potential scheme for an effective TCO film-embedded heterojunction Si solar cell.
TL;DR: In this paper, the TVK8 envelope function Hamiltonian was used to predict the band gap of type II InAs/GaSb superlattices in which the layer widths are known with a typical uncertainty of 0.2 ML.
TL;DR: In this paper, the band alignment properties of atomic layer hafnium oxide (HfO2) film deposited on crystallographically oriented epitaxial Ge were investigated using x-ray photoelectron spectroscopy (XPS).
Abstract: Crystallographically oriented epitaxial Ge layers were grown on (100), (110), and (111)A GaAs substrates by in situ growth process using two separate molecular beam epitaxy chambers. The band alignment properties of atomic layer hafnium oxide (HfO2) film deposited on crystallographically oriented epitaxial Ge were investigated using x-ray photoelectron spectroscopy (XPS). Valence band offset, ΔEv values of HfO2 relative to (100)Ge, (110)Ge, and (111)Ge orientations were 2.8 eV, 2.28 eV, and 2.5 eV, respectively. Using XPS data, variation in valence band offset, ΔEV(100)Ge>ΔEV(111)Ge>ΔEV(110)Ge, was obtained related to Ge orientation. Also, the conduction band offset, ΔEc relation, ΔEc(110)Ge>ΔEc(111)Ge>ΔEc(100)Ge related to Ge orientations was obtained using the measured bandgap of HfO2 on each orientation and with the Ge bandgap of 0.67 eV. These band offset parameters for carrier confinement would offer an important guidance to design Ge-based p- and n-channel metal-oxide field-effect transistor for low...
TL;DR: In this paper, the authors studied the interface formation between the perovskite oxides SrTiO3 and BiFeO3 using in situ photoelectron spectroscopy by depositing BiFeOns on Sr TiO3, and vice versa via pulsed laser deposition.
Abstract: The interface formation between the perovskite oxides SrTiO3 and BiFeO3 was studied using in situ photoelectron spectroscopy by depositing BiFeO3 on SrTiO3 and vice versa via pulsed laser deposition. For the interfaces characterized, a type II band alignment with a valence band offset of 0.9–1.0 eV and a conduction band offset of 0.5–0.6 eV was observed. Within the margin of error the commutativity was fulfilled for the SrTiO3/BiFeO3 interface, meaning that the band alignment does not depend on the deposition sequence.
TL;DR: This work proposes a new class of solid-state PECs based on mixed ionic and electronic conducting (MIEC) oxides that operates at temperatures significantly above ambient and utilizes both the light and thermal energy available from concentrated sunlight to dissociate water vapor.
Abstract: Photoelectrochemical cells (PECs) have been studied extensively for dissociating water into hydrogen and oxygen. Key bottlenecks for achieving high solar-to-hydrogen efficiency in PECs include increasing solar spectrum utilization, surmounting overpotential losses, and aligning the absorber/electrochemical redox levels. We propose a new class of solid-state PECs based on mixed ionic and electronic conducting (MIEC) oxides that operates at temperatures significantly above ambient and utilizes both the light and thermal energy available from concentrated sunlight to dissociate water vapor. Unlike thermochemical and hybrid photo-thermochemical water-splitting routes, the elevated-temperature PEC is a single-step approach operating isothermally. At the heart of the solid-state PEC is a semiconductor light absorber coated with a thin MIEC layer for improved catalytic activity, electrochemical stability, and ionic conduction. The MIEC, placed between the gas phase and the semiconductor light absorber, provides a facile path for minority carriers to reach the water vapor as well as a path for the ionic carriers to reach the solid electrolyte. Elevated temperature operation allows reasonable band misalignments at the interfaces to be overcome, reduces the required overpotential, and facilitates rapid product diffusion away from the surface. In this work, we simulate the behavior of an oxygen-ion-conducting photocathode in 1-D. Using the detailed-balance approach, in conjunction with recombination and electrochemical reaction rates, the practical efficiency is calculated as a function of temperature, solar flux, and select material properties. For a non-degenerate light absorber with a 2.0 eV band-gap and an uphill band offset of 0.3 eV, an efficiency of 17% and 11% is predicted at 723 and 873 K, respectively.
TL;DR: In this article, the authors measured the band offsets at the interfaces of n- and p-type InP ((100) and (111)A) and atomic-layer-deposited (ALD) Al2O3 were measured with internal photoemission and spectroscopic ellipsometry.
Abstract: Band offsets at the interfaces of n- and p-type InP ((100) and (111)A) and atomic-layer-deposited (ALD) Al2O3 were measured with internal photoemission and spectroscopic ellipsometry. Similarly, the band offsets at the interface of semi-insulating InP (100) and ALD HfO2 were also determined. The barrier between the top of InP valence band (VB) and the bottom of Al2O3 conduction band (CB) is found to be 3.44 eV for p-type material and 3.53 eV for n-type. The photoemission thresholds are found to be sensitive to the annealing conditions, and blue shifts are observed after annealing. The offsets from InP valence band to the HfO2 conduction band for the HfO2/InP stack are found to be 3.89 eV, and we observed an increase of 60 meV if the InP surface is passivated.