Showing papers on "Band offset published in 2006"
TL;DR: Spectrally resolved photocurrent measurements on single self-assembled nanowire heterostructures believe that these wires form promising candidates as nanoscale infrared polarization-sensitive photodetectors.
Abstract: We report on spectrally resolved photocurrent measurements on single self-assembled nanowire heterostructures. The wires, typically 3 microm long with an average diameter of 85 nm, consist of InAs with a 1 microm central part of InAsP. Two different sets of wires were prepared with phosphorus contents of 15+/-3% and 35+/-3%, respectively, as determined by energy-dispersive spectroscopy measurements made in transmission electron microscopy. Ohmic contacts are fabricated to the InAs ends of the wire using e-beam lithography. The conduction band offset between the InAs and InAsP regions virtually removes the dark current through the wires at low temperature. In the optical experiments, interband excitation in the phosphorus-rich part of the wires results in a photocurrent with threshold energies of about 0.65 and 0.82 eV, respectively, in qualitative agreement with the expected band gap of the two compositions. Furthermore, a strong polarization dependence is observed with an order of magnitude larger photocurrent for light polarized parallel to the wire than for light polarized perpendicular to the wire. We believe that these wires form promising candidates as nanoscale infrared polarization-sensitive photodetectors.
227 citations
TL;DR: In this article, the energy-band gap of the Al2O3-InGaAs interface was determined to be 3.83±0.05eV by x-ray photoelectron spectroscopy.
Abstract: The valence-band offset has been determined to be 3.83±0.05eV at the atomic-layer-deposition Al2O3∕InGaAs interface by x-ray photoelectron spectroscopy. The Au–Al2O3∕InGaAs metal-oxide-semiconductor diode exhibits current-voltage characteristics dominated by Fowler-Nordheim tunneling. From the current-voltage data at forward and reverse biases, a conduction-band offset of 1.6±0.1eV at the Al2O3–InGaAs interface and an electron effective mass ∼0.28±0.04m0 of the Al2O3 layer have been extracted. Consequently, combining the valence-band offset, the conduction-band offset, and the energy-band gap of the InGaAs, the energy-band gap of the atomic-layer-deposited Al2O3 is 6.65±0.11eV.
179 citations
TL;DR: This work demonstrates that care must be taken when using carboxylic acid side groups to attach polymers to titania surfaces in photovoltaic cells, if the density of attachment groups is just enough to attach the polymer, then the benefits of the interface modifier can be realized without substantially decreasing the open-circuit voltage.
Abstract: The interface of planar TiO2/polymer photovoltaic cells was modified with two carboxylated polythiophenes having different densities of carboxylic acid groups. Both of the interface modifiers increase the photocurrent of the cells but lower the open-circuit voltage. The work function of the TiO2, measured using a Kelvin probe, increases with increasing density of carboxylic acid groups due to the formation of interfacial dipoles pointing toward the TiO2 surface. The formation of interfacial dipoles results in a shift in the band offset at the TiO2/polymer interface, which explains the decrease in the open-circuit voltage. This work demonstrates that care must be taken when using carboxylic acid side groups to attach polymers to titania surfaces in photovoltaic cells. If the density of attachment groups is just enough to attach the polymer, then the benefits of the interface modifier can be realized without substantially decreasing the open-circuit voltage.
99 citations
Patent•
15 Jun 2006TL;DR: In this paper, a core/multishell semiconductor nanocrystal comprising a core and multiple shells, which exhibits a type-I band offset and high photoluminescence quantum yield providing bright tunable emission covering the visible range from about 400 nm to NIR over 1600 nm.
Abstract: The present invention provides a core/multishell semiconductor nanocrystal comprising a core and multiple shells, which exhibits a type-I band offset and high photoluminescence quantum yield providing bright tunable emission covering the visible range from about 400 nm to NIR over 1600 nm.
92 citations
TL;DR: In this paper, the growth of homogeneous InAs1-xPx nanowires as well as InAs 1-xpx heterostructure segments was studied as a function of TBP/TBAs ratio, temperature and diameter of the wires.
Abstract: We present the growth of homogeneous InAs1-xPx nanowires as well as InAs1-xPx heterostructure segments in InAs nanowires with P concentrations varying from 22% to 100%. The incorporation of P has been studied as a function of TBP/TBAs ratio, temperature, and diameter of the wires. The crystal structure of the InAs as well as the InAs1-xPx segments were found to be wurtzite as determined from high-resolution transmission electron microscopy. Furthermore, temperature-dependent electrical transport measurements were performed on individual heterostructured wires to extract the conduction band offset of InAs1-xPx relative to InAs as a function of composition. From these measurements we extract a value of the linear coefficient of the conduction band versus x of 0.6 eV and a nonlinear coefficient, or bowing parameter, of 0.2 eV. Finally, homogeneous InAs0.8P0.2 nanowires were shown to have a nondegenerate n-type doping and function as field-effect transistors at room temperature. (Less)
81 citations
TL;DR: In this paper, the energy diagrams of interfaces between (100)Ge and several rare-earth oxide insulators deposited from a molecular beam are determined using a combination of internal photoemission and photoconductivity measurements.
Abstract: Energy diagrams of interfaces between (100)Ge and several rare-earth oxide insulators deposited from a molecular beam are determined using a combination of internal photoemission and photoconductivity measurements. For the wide band gap (5.9eV) oxides Gd2O3 and LaHfOx, the band alignment at the interface is found to be close to that of HfO2 and is characterized by conduction/valence band offsets of ∼2∕∼3eV. In contrast, CeO2 which has a much narrower band gap (3.3eV) does not provide a band alignment diagram corresponding to sufficient insulation.
57 citations
TL;DR: The effect of nitrogen incorporation on the electronic structure and thermal stability of HfO2 gate dielectric was investigated by using photoemission study and first-principles calculation as mentioned in this paper.
Abstract: The effect of nitrogen incorporation on the electronic structure and thermal stability of HfO2 gate dielectric was investigated by using photoemission study and first-principles calculation. Hafnium oxynitride (HfON) dielectric shows higher thermal stability in comparison to pure HfO2 on Si. Atomic N can passivate O vacancies in the dielectrics during nitridation process, but the N atoms incorporated into interstitial sites cause band gap reduction. Postnitridation annealing is required to activate interstitial N atoms to form stable N–Hf bonds, which will increase the band gap and band offset of as-nitrided dielectric film.
57 citations
TL;DR: In this paper, the electronic properties of Si1−xGex alloys epitaxially grown on (001) Si 1−yGey relaxed substrates for any x and y Ge concentrations are presented.
Abstract: The electronic properties of strained Si1−xGex alloys epitaxially grown on (001) Si1−yGey relaxed substrates for any x and y Ge concentrations are presented here. Our calculations are based on an sp3d5s* nearest-neighbour tight-binding Hamiltonian and exploit appropriate scaling laws of the Hamiltonian interactions to account for strain effects. Spin–orbit interaction is also included in the Hamiltonian. We first provide the valence and conduction band offsets at the heterointerfaces between Si1−xGex and Si1−yGey, as well as the fundamental energy gap for Si1−xGex strained alloys. We are thus able to distinguish the region in the (x,y) plane where robust type-I alignment is achieved. Then this information on band alignment is exploited to propose a heterostructure which is both type I in -space and direct in -space. With this aim we adopt the decimation–renormalization method for the determination of the electronic properties of the multilayer structure; from the Green's function the energy spectrum and the partial and the total densities of states projected on each layer of the system are obtained. Our conclusion is that by suitable control of alloying, stress, band offsets and folding, truly direct (both in - and in -space) semiconducting heterostructures based on silicon and germanium can be realized. As an example, the case of pure Ge sandwiched between Si0.25Ge0.75 alloys, grown on a Si0.2Ge0.8 substrate, is fully discussed.
56 citations
TL;DR: In this article, X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band (ΔEv) of MgO∕GaN heterostructures.
Abstract: MgO is a promising gate dielectric and surface passivation film for GaN transistors but little is known of the band offsets in the MgO∕GaN system. X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band (ΔEv) of MgO∕GaN heterostructures in which the MgO was grown by rf plasma-assisted molecular beam epitaxy on top of thick GaN templates on sapphire substrates. A value of ΔEv=1.06±0.15eV was obtained by using the Ga 3d energy level as a reference. Given the experimental band gap of 7.8eV for the MgO, this would indicate a conduction band offset ΔEC of 3.30eV in this system.
53 citations
TL;DR: In this article, the experimental data on band alignments of high-k Er2O3 films epitaxially grown on Si substrates by molecular beam epitaxy are reported by using x-ray photoelectron spectroscopy.
Abstract: The experimental data on band alignments of high-k Er2O3 films epitaxially grown on Si substrates by molecular beam epitaxy are reported By using x-ray photoelectron spectroscopy, the valence and the conduction-band offsets of Er2O3 to Si are obtained to be 31±01 and 35±03eV, respectively, showing a roughly symmetrical offset at the conduction and the valence band The energy gap of Er2O3 is determined to be 76±03eV From the band offset viewpoint, those obtained numbers indicate that Er2O3 could be a promising candidate for high-k gate dielectrics
49 citations
TL;DR: In this article, X-ray photoelectron spectroscopy has been used to measure the valence-band offset at the MgO-GaAs(001) heterojunction interface.
Abstract: The electronic band structure at the interface of the MgO-GaAs(001) tunnel contact has been experimentally studied. X-ray photoelectron spectroscopy has been used to measure the valence-band offset at the MgO-GaAs(001) heterojunction interface. The valence-band offset ΔEV is determined to be 4.2±0.1eV. As a consequence, a nested “type-I” band alignment with a conduction-band offset of ΔEC=2.2±0.1eV is found. The accurate determination of the valence and conduction band offsets is important for the fundamental understanding of the tunnel spin injection in GaAs.
TL;DR: In this article, the dependence of the active layer structure on the performance of the deep-UV AlGaN light-emitting diodes was theoretically investigated with an APSYS simulation program.
Abstract: The dependence of the active-layer structure on the performance of the deep-UV AlGaN light-emitting diodes (LEDs) was theoretically investigated with an APSYS simulation program. Several structure parameters such as well width, well number, barrier height, barrier width, and doping type were employed to study how these parameters change the band structures as well as the carrier distributions. The band offset and bowing parameter used in the theoretical analysis were extracted from the experimental results. Theoretical analysis shows that the nonuniform carrier distributions as well as the low hole concentrations, which caused by polarization-induced tilted band structures, play important roles in improving the performance of the AlGaN LEDs. Compensating this asymmetric band structure and increasing the hole density are the important keys to improve the AlGaN LED performance. Numerical simulation results suggest that the higher output power can be obtained when the active layer consists of only one quantum well with a width of 1-3 nm and two thicker n-doped barriers with a small Al composition
TL;DR: In this paper, the authors studied the properties of the hafnia or hafnium oxide and the silicate layer at the Si/HfO 2 interface and found that the low conduction band states are composed mainly by d states instead of s and p states as is in the case for SiO 2.
TL;DR: In this paper, the authors measured the energy discontinuity in the valence band (ΔEv) of Sc2O3∕GaN heterostructures using x-ray photoelectron spectroscopy.
Abstract: The Sc2O3∕GaN interface shows low trap densities and has been used both to demonstrate inversion in gated metal-oxide-semiconductor diodes and to mitigate current collapse in AlGaN∕GaN heterostructure transistors but little is known of the band offsets at this interface. We measured the energy discontinuity in the valence band (ΔEv) of Sc2O3∕GaN heterostructures using x-ray photoelectron spectroscopy. A value of ΔEv=0.42±0.07eV was obtained using the Ga 3d energy level as a reference. With the experimental band gap of 6.0eV for the Sc2O3 grown by this method, this implies that the conduction band offset ΔEC is 2.14eV in this system.
TL;DR: In this article, the authors investigated the interface energy barriers induced on (001) silicon by La2Hf2O7, whose growth has been recently attained by molecular-beam epitaxy.
Abstract: In the perspective of exploring alternative gate dielectrics for the future generation of microelectronic devices, we investigated experimentally and theoretically the interface energy barriers induced on (001) silicon by La2Hf2O7, whose growth has been recently attained by molecular-beam epitaxy. Experimental results show that the 5.6±0.1eV band gap of La2Hf2O7 is aligned to the band gap of silicon with a valence band offset of 2.4±0.1eV and a conduction band offset of 2.1±0.1eV. Density functional theory calculations yield valence band offset values ranging between 1.8 and 2.4eV.
TL;DR: In this paper, high performance floating-gate memory devices of Si nanocrystal (NC) dots on HfO2 gate oxide were fabricated at temperatures below 400°C and a large counterclockwise hysteresis of 5.2V at an applied voltage of +6V, and a stored charge density of 6×1012cm−2 were observed.
Abstract: High-performance floating gate memory devices of Si nanocrystal (NC) dots on HfO2 gate oxide were fabricated at temperatures below 400°C. A large counterclockwise hysteresis of 5.2V, at an applied voltage of +6V, and a stored charge density of 6×1012cm−2 were observed. Moreover, the smaller band offset of the high-κ tunneling layer resulted in higher charge tunneling probabilities towards the Si NC dots than those observed with a SiO2 tunneling layer. Advantages in terms of scaling for a high-performance and stable reliability memory device are confirmed.
TL;DR: In this article, contactless electroreflectance spectroscopy (CER) was used to study the optical transitions in GaNyAs1−y/GaAs multi quantum well (MQW) samples with y=0.012 and 0.023.
TL;DR: In this paper, the second nearest neighbor (2 nn) sp 3 s ⁎ semi-empirical tight binding formalism including spin-orbit coupling was used to calculate the electronic band structure of Cd based group II-VI ternary/binary heterostructures.
TL;DR: In this paper, the composition and uniformity of La-silicate film were simulated from the ratio of photoelectron intensity, I La 4d /I Si 2p, using angle resolved X-ray photo-electron spectroscopy.
TL;DR: In this article, transparent conductive In2O3 films were deposited by reactive evaporation of In and analyzed in-situ with photoelectron spectroscopy, and a valence band offset ΔEVB=2.1±0.1 eV was determined.
Abstract: Transparent conductive In2O3 films were deposited by reactive evaporation of In and analyzed in-situ with photoelectron spectroscopy. The interface formation of In2O3 with evaporated CdTe has been investigated using the same technique. A valence band offset ΔEVB=2.1±0.1 eV is determined, resulting in a negligible conduction band offset. However, In2O3 will not provide an Ohmic contact to n-CdTe, due to the Fermi level position at the interface.
TL;DR: In this paper, the authors proposed an approach to stabilize the cubic zinc-blende (ZB) phase of semiconductor compounds that are usually more stable in the hexagonal wurtzite (WZ) phase.
Abstract: We propose an approach to stabilize the cubic zinc-blende (ZB) phase of semiconductor compounds that are usually more stable in the hexagonal wurtzite (WZ) phase. This approach is based on impurity doping and we take advantage of the band offset between the ZB and WZ phases. We show that introduction of donors should stabilize the one with lower conduction band (ZB), whereas holes should stabilize the one with higher valence band (WZ). A mechanism to invert the valence band offset is proposed in order to stabilize the ZB phase through holes. We used GaN, ZnO, and AlN as examples.
TL;DR: In this paper, the fundamental and imperfection-related components of the electron state density at interfaces of (1 − 0)Ge with several high-κ oxides have been investigated by a set of complementary methods to reveal general trends in their evolution.
TL;DR: In this paper, an automatic optimization loop based on Nelder-Mead simplex optimization algorithm has been implemented to obtain optimal CIGS absorber's band-gap grading profile.
TL;DR: The calculated band offset shows a staggered band line-up, with the heterojunction forming a one-dimensional array of quantum dots, and two different types of junction occur, and net charges of opposite signs appear in each of them.
Abstract: The energetic, electronic and structural properties of a heterojunction formed by BN and AlN (10,0) nanotubes have been studied using first principles density functional theory. The differences between the AlN and BN nanotubes lead to structural rearrangements mainly at the junction layers. Two different types of junction occur, and net charges of opposite signs appear in each of them, with a resulting electric dipole along the heterojunction axis. The calculated band offset shows a staggered band line-up, with the heterojunction forming a one-dimensional array of quantum dots.
TL;DR: The conduction band offset of n-ZnO∕n-6H-SiC heterostructures fabricated by rf-sputtered ZnO on commercial n-type 6HSiC substrates has been measured by a variety of methods as discussed by the authors.
Abstract: The conduction band offset of n-ZnO∕n-6H-SiC heterostructures fabricated by rf-sputtered ZnO on commercial n-type 6H-SiC substrates has been measured by a variety of methods. Temperature dependent current-voltage characteristic, photocapacitance, and deep level transient spectroscopy measurements showed the conduction band offsets to be 1.25, 1.1, and 1.22eV, respectively.
TL;DR: In this article, the optical and electrical properties of the high permittivity (κ) metal oxides, HfTiO and HfTaTiO, using HfO2 as a reference and compared their material properties against their electrical performance.
Abstract: The authors investigated the optical and electrical properties of the high permittivity (κ) metal oxides, HfTiO and HfTaTiO, using HfO2 as a reference and compared their material properties against their electrical performance. HfTiO has a higher κ value but its band offset is relatively smaller and, therefore, it has greater gate leakage current than HfO2. HfTaTiO has an even higher κ value which compensates for the impact of its small band offset. In addition, HfO2 was found to have more defect states than the other two films, which caused a larger hysteresis in the capacitance-voltage scan and degraded channel mobility.
TL;DR: In this paper, the results of comparative XPS and PYS studies of electronic properties of the space charge layer of the L-CVD SnO2 thin films after air exposure and subsequent UHV annealing at 400°C, with a special emphasis on the interface Fermi level position has been determined.
TL;DR: In this paper, a two-colour infrared detector with photoresponse peaks at ∼6 and ∼17 μm at room temperature is discussed. And the authors describe multiband photon detectors based on semiconductor micro-and nano-structures.
Abstract: The work describes multiband photon detectors based on semiconductor micro-and nano-structures. The devices considered include quantum dot, homojunction, and heterojunction structures. In the quantum dot structures, transitions are from one state to another, while free carrier absorption and internal photoemission play the dominant role in homo or heterojunction detectors. Quantum dots-in-a-well (DWELL) detectors can tailor the response wavelength by varying the size of the well. A tunnelling quantum dot infrared photodetector (T-QDIP) could operate at room temperature by blocking the dark current except in the case of resonance. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunnelling, while the dark current is blocked by AlGaAs/InGaAs tunnelling barriers placed in the structure. A two-colour infrared detector with photoresponse peaks at ∼6 and ∼17 μm at room temperature will be discussed. A homojunction or heterojunction interfacial workfunction internal photoemission (HIWIP or HEIWIP) infrared detector, formed by a doped emitter layer, and an intrinsic layer acting as the barrier followed by another highly doped contact layer, can detect near infrared (NIR) photons due to interband transitions and mid/far infrared (MIR/FIR) radiation due to intraband transitions. The threshold wavelength of the interband response depends on the band gap of the barrier material, and the MIR/FIR response due to intraband transitions can be tailored by adjusting the band offset between the emitter and the barrier. GaAs/AlGaAs will provide NIR and MIR/FIR dual band response, and with GaN/AlGaN structures the detection capability can be extended into the ultraviolet region. These detectors are useful in numerous applications such as environmental monitoring, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing.
TL;DR: In this paper, the optical properties of lattice-matched InP/AlxGa1?xAsSb layers for 0? x? 0.17 have been investigated by photoluminescence (PL) spectroscopy at 15 K.
Abstract: The optical properties of lattice-matched InP/AlxGa1?xAsSb layers for 0 ? x ? 0.17 have been investigated by photoluminescence (PL) spectroscopy at 15 K. The PL revealed emission peaks corresponding to the band-to-band transitions of AlGaAsSb and InP. Moreover, a second emission due to the spatially indirect recombination (type-II) of electrons in the conduction band (CB) of InP and holes in the valence band (VB) of AlGaAsSb was also observed. The CB and VB offsets between InP and AlGaAsSb are determined for different Al concentrations directly from the measured transitions. Furthermore, the strong type-II PL shift induced by varying the excitation intensity is compared to theoretical predictions.
TL;DR: In this article, a p-channel flash device with a SiGe layer is proposed, which is based on the analysis made with the simulator MEDICI, to enhance the band-to-band tunneling current and improve the programming speed.
Abstract: A novel p-channel flash device with a SiGe layer is proposed, which is based on the analysis made with the simulator MEDICI, to enhance the band-to-band-tunneling current and improve the programming speed. The programming biases of the p-channel flash device can be reduced with an equal programming speed. Simulation results show that more than one hundred times enhancement in the programming speed or 35% reduction of the drain voltage can be achieved in the proposed p-channel flash device with a 40% Ge content in the surface SiGe layer. In addition, a Si-cap layer is inserted between the SiGe and the tunneling oxide to obtain a high-quality interface and to optimize the cell structure