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1 Nov 2006

Volume 100, Issue 9, Articles (09xxxx)

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Synthesis and analysis of Ag-doped ZnO

Byung Du Ahn, Hong Seong Kang, Jong Hoon Kim, Gun Hee Kim, Hyun Woo Chang, and Sang Yeol Lee

J. Appl. Phys. 100, 093701 (2006); http://dx.doi.org/10.1063/1.2364041 (6 pages) | Cited 29 times

Online Publication Date: 1 November 2006

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The solid-solid interaction and thermal decomposition behavior of 2 wt % Ag2O in ZnO powder have been investigated by using thermogravimetry analysis and differential thermal analysis. Ag2O, which remained stable in ZnO up to 200 °C, was observed to be thermally decomposed to Ag+ ions in the temperature range of 200–250 °C, suggesting that Ag+ ions were diffused into ZnO matrix. Based on thermal analysis, ZnO:Ag films have been fabricated on a (001) Al2O3 substrate using specifically synthesized Ag-doped ZnO target by pulsed laser deposition. The effect of (002) peak shift on the structural property of Ag-doped ZnO films has been systematically characterized to investigate the influence of the substitution of Ag+ for Zn+. Ag-doped p-type ZnO films have been successfully grown at a deposition temperature in the range of 200–250 °C, which is in good agreement with thermally decomposed temperature for Ag2O to Ag+ in ZnO powder, with hole concentrations of 4.9×1016–6.0×1017 cm−3, hole mobilities of 0.29–2.32 cm2/V s, and resistivities of 34–54 Ω cm. The effect of Ag doping in ZnO thin film has been systematically investigated and the p-type conduction mechanism has been proposed.
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81.15.Fg Pulsed laser ablation deposition
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
73.61.Ga II-VI semiconductors

Quantized acoustoelectric single electron transport close to equilibrium

F. J. Ahlers, O. F. O. Kieler, B. E. Sağol, K. Pierz, and U. Siegner

J. Appl. Phys. 100, 093702 (2006); http://dx.doi.org/10.1063/1.2364451 (6 pages) | Cited 5 times

Online Publication Date: 1 November 2006

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Single electron transport driven by surface acoustic waves (SAWs) is studied in the low power regime. The measurements are performed on a one-dimensional (1D) channel in a GaAs/AlGaAs split-gate structure that is not dominated by unintentional impurities. The effective electric amplitude of the SAW is calibrated with the 1D subband energy splitting of the channel. Using this calibration, a close-to-equilibrium transport regime is identified, in which the SAW amplitude is on the order of the 1D subband energy splitting. In a proof of principle experiment, a quantized current I = 1ef (f, frequency of the SAW; e, elementary charge) is generated close to equilibrium. Compared to the extensively studied nonequilibrium regime at high acoustic powers, heating is reduced close to equilibrium. This may improve the precision of quantum current standards based on SAW driven single electron transport.
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73.63.-b Electronic transport in nanoscale materials and structures
72.50.+b Acoustoelectric effects
68.35.Iv Acoustical properties
61.72.S- Impurities in crystals

Band lineup of pseudomorphic GaAs1−xSbx quantum-well structures with GaAs, GaAsP, and InGaP barriers grown by metal organic chemical vapor deposition

M. S. Noh, J. H. Ryou, R. D. Dupuis, Y.-L. Chang, and R. H. Weissman

J. Appl. Phys. 100, 093703 (2006); http://dx.doi.org/10.1063/1.2363237 (6 pages)

Online Publication Date: 2 November 2006

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We report the growth of thin pseudomorphic GaAs1−xSbx (x ∼ 0.3) quantum-well heterostructures by metal-organic chemical vapor deposition and the measurement of the band lineups for the heterointerface of GaAs1−xSbx (x ∼ 0.3) quantum wells with GaAs, GaAs0.86P0.14, and In0.5Ga0.5P quantum-well barriers for 80 Å double-quantum-well heterostructures using excitation-dependent cathodoluminescence measurements at 10 K. GaAs1−xSbx (x ∼ 0.3) quantum wells with GaAs and GaAs0.86P0.14 barriers show type-II band alignment, while GaAs1−xSbx (x ∼ 0.3) quantum wells with In0.5Ga0.5P barriers exhibit a type-I band lineup. The type-I/type-II band alignment boundary condition as a function of the GaAs1−xSbx quantum-well composition and of the barrier materials and compositions is calculated. The pseudomorphic GaAs1−xSbx/GaAs quantum-well heterointerface is estimated to have a type-II alignment. For GaAs1−xSbx/GaAsP and GaAs1−xSbx/InGaP heterostructures, both type-I and type-II alignments can occur depending on the quantum-well and barrier compositions. As the Sb composition of the quantum well increases, higher P alloy composition (in GaAsP barriers) and Ga (in InGaP barriers) composition are required in order to make the type-II to type-I transition.
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73.20.At Surface states, band structure, electron density of states
73.21.Fg Quantum wells
78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhanced colossal electroresistance in Cu/Pr0.7Ca0.3MnO3/Cu structure

W. C. Peng, J. G. Lin, and J. H. Wu

J. Appl. Phys. 100, 093704 (2006); http://dx.doi.org/10.1063/1.2361087 (3 pages) | Cited 9 times

Online Publication Date: 6 November 2006

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Voltage-current (V-I) curves have been measured in symmetrical metal/Pr0.7Ca0.3MnO3/metal structures with metal = Ag, Cu, Pt, and Au. Our four measured samples exhibit room-temperature nonlinear and asymmetric V-I curves with electrical hysteresis loops. Among these four samples, Cu/Pr0.7Ca0.3MnO3/Cu produces the largest hysteresis loop, yielding an enhanced colossal electroresistance of 2279% at a current of 0.5 A.
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73.40.Rw Metal-insulator-metal structures

Transport and noise in resonant tunneling diode using self-consistent Green’s function calculation

V. Nam Do, P. Dollfus, and V. Lien Nguyen

J. Appl. Phys. 100, 093705 (2006); http://dx.doi.org/10.1063/1.2364035 (7 pages) | Cited 8 times

Online Publication Date: 7 November 2006

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The fully self-consistent nonequilibrium Green’s function approach to quantum transport is developed to investigate one-dimensional nanoscale devices. Numerical calculations performed for resonant tunneling diodes of different designs and at different temperatures show reasonable results for the potential and electron density profiles, as well as for the transmission coefficient and the current-voltage characteristics. The resonant behavior is discussed in detail with respect to the quantum-well width, the barrier thickness, and the temperature. It is also shown that the current noise spectral density can be straightforwardly calculated for both the coherent and the sequential tunneling models. In qualitative agreement with experiments, the obtained results highlight the role of charge interaction, which causes a fluctuation of the density of states in the well and therefore a noise enhancement in the negative differential conductance region.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling

The electronic properties of amorphous and crystallized In2O3 films

Hiromi Nakazawa, Yuko Ito, Eiji Matsumoto, Kenji Adachi, Nobuyuki Aoki, and Yuichi Ochiai

J. Appl. Phys. 100, 093706 (2006); http://dx.doi.org/10.1063/1.2358829 (8 pages) | Cited 23 times

Online Publication Date: 7 November 2006

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Polycrystalline In2O3 films with high crystallinity were prepared by annealing the amorphous In2O3 films deposited at room temperature by using dc/rf sputtering method. General electronic behaviors of both these amorphous and polycrystalline films have been investigated by means of Hall effect and resistivity measurements at temperatures between 4.2 and 300 K. For the amorphous films, ionized impurity scattering dominates the electronic transport, and Hall mobility agrees well with the theory of degenerate semiconductors with divalent impurity scattering centers. On the other hand, the conduction mechanism of the polycrystalline films is governed dominantly by phonon scattering, since these films exhibit a clearly positive temperature coefficient of resistivity with the maximum Hall mobility of 150 cm2/V s at 300 K and 230 cm2/V s at 4.2 K, with little change in carrier concentration between these temperatures. Conductivity of both the amorphous and polycrystalline films is found to show a linear relationship in a double-logarithmic plot against carrier concentration between 4×1015 and 5×1020 cm−3, a typical behavior of the impurity semiconductors with parabolic conduction band. For each set of films with the same thermal history, Hall mobility is found to vary on a convex upward curve with respect to carrier concentration. This behavior suggests a general and strong correlation of the structural defects introduced upon deposition and localization of conduction electrons with electron mobility, which led to a proposition of three categories for temperature coefficient of resistivity with major transport mechanisms of phonon scattering, divalent impurity scattering, and weak localization, respectively.
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73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.20.My Galvanomagnetic and other magnetotransport effects
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
68.55.A- Nucleation and growth

Morphology and electronic properties of the pentacene on cobalt interface

M. V. Tiba, W. J. M. de Jonge, B. Koopmans, and H. T. Jonkman

J. Appl. Phys. 100, 093707 (2006); http://dx.doi.org/10.1063/1.2363707 (6 pages) | Cited 14 times

Online Publication Date: 8 November 2006

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In this paper, we report the structural and electronic properties of pentacene thin films grown on a polycrystalline Co film using atomic force microscopy and ultraviolet photoemission spectroscopy (UPS), respectively. Investigation of this type of interface is of importance for the engineering of hybrid organometallic spintronic devices for which the use of spin polarized electrodes is a prerequisite. Uniform single crystalline areas of pentacene as large as several micrometers, with molecules arranging almost perpendicular to the substrate, were obtained. For the electronic properties at this interface, we have found an energy barrier for the hole injection of about 1 eV, in spite of the fact that the ionization potential of pentacene reported previously equals the work function of Co. A shift of the vacuum level of the same magnitude has also been observed. A comparison of the UPS spectra of the pentacene films with the gas phase spectrum directly indicates that hybridization effects are present at this interface.
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68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states

Effect of dislocations on open circuit voltage in crystalline silicon solar cells

Thomas Kieliba, Stephan Riepe, and Wilhelm Warta

J. Appl. Phys. 100, 093708 (2006); http://dx.doi.org/10.1063/1.2360773 (6 pages) | Cited 2 times

Online Publication Date: 8 November 2006

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The dislocation dependence of open circuit voltage is studied based on Donolato’s model for the effect of dislocations on minority carrier effective diffusion length [ J. Appl. Phys. 84, 2656 (1998) ]. Experimental data measured on thin-film solar cells show a strong decrease of open circuit voltage Voc with an increase in defect density. The analysis of the recombination currents indicates that Voc is largely reduced by space charge region recombination. For a quantitative study on the relationship between dislocation density, effective diffusion length, and Voc the data are fitted with an extended version of Donolato’s model. Taking into account the base recombination current as well as the space charge region recombination current, the modeled curves fit very well to the experimental data. However, satisfactory fitting results require that the region of high recombination is set wider than the “effective depletion region width,” which is calculated from the electrical field strength in a planar p‐n junction. This effect can be explained with the assumption of a geometrical enlargement of the p‐n junction due to defects like dislocations.
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84.60.Jt Photoelectric conversion
61.72.Bb Theories and models of crystal defects

Characteristics of InGaPN/GaAs heterostructures investigated by photoreflectance spectroscopy

T. S. Wang, K. I. Lin, and J. S. Hwang

J. Appl. Phys. 100, 093709 (2006); http://dx.doi.org/10.1063/1.2358327 (6 pages) | Cited 2 times

Online Publication Date: 9 November 2006

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Photoreflectance (PR) spectra at various temperatures and photoluminescence (PL) spectra and high-resolution x-ray rocking curve (XRC) measurements are used to investigate the band alignment, epitaxial-strain, and atomic-ordering effects in In0.54Ga0.46P1−yNy/GaAs (y = 0%–2.0%) heterostructures. The existence of additional peaks in PR spectra at higher levels of nitrogen (N) incorporation implies that the band alignment switches from type I to type II, due to the lowering of the conduction band. The electric field at the interface is determined and is discussed with the N content. Redshifts of the PR and PL peaks indicate that the band gap of InGaPN is dramatically reduced as N is incorporated. The valence-band splitting (VBS) and the spin-orbit splitting of InGaPN are obtained from PR spectra. High-resolution XRC measurements indicate that as the N content increases, the lattice mismatch and the compressive strain between the epilayer and GaAs substrate decrease while the VBS increases, which implies an increase in the degree of ordering in InGaPN caused by the transition from a cubic zinc blende structure to a [111] CuPt structure. The order parameter η of InGaPN deduced from the VBS ranges from 0.256 to 0.498, indicating that the InGaPN epilayer becomes more ordered with increasing N incorporation.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
64.70.K- Solid-solid transitions

Preparation and thermoelectric properties of sintered Fe1−xCoxTe2 (0 ≤ x ≤ 0.4)

Kengo Kishimoto, Kento Kondo, and Tsuyoshi Koyanagi

J. Appl. Phys. 100, 093710 (2006); http://dx.doi.org/10.1063/1.2361088 (4 pages)

Online Publication Date: 9 November 2006

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Polycrystalline samples of FeTe2 substituted with Co were prepared by powder metallurgy, and their thermoelectric properties were investigated. When the substitution amount x increased to 0.4, their electrical conductivity increased to approximately 2000 S/cm at room temperature and their lattice thermal conductivity decreased to 10 mW cm−1 K−1 at high temperatures. A maximum dimensionless figure of merit of 0.13 was obtained for Fe0.8Co0.2Te2 at 700 K. The electronic structure of FeTe2 was also calculated, and the possibility of improving its thermoelectric performance of FeTe2 is discussed.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.15.Jf Thermoelectric and thermomagnetic effects

Characterization of organic photovoltaic devices with indium-tin-oxide anode treated by plasma in various gases

Z. R. Hong, C. J. Liang, X. Y. Sun, and X. T. Zeng

J. Appl. Phys. 100, 093711 (2006); http://dx.doi.org/10.1063/1.2372574 (4 pages) | Cited 19 times

Online Publication Date: 9 November 2006

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Indium-tin-oxide (ITO) anode treated by different gas plasma or UV ozone has been used for photovoltaic (PV) cells with structure of ITO/copper phthalocyanine (CuPc)/C60/bathocuproine/Al. Both surface energy and work function of the ITO substrates were affected by these treatments. However, the main performance parameters of PV cells, including short circuit current, open circuit voltage, power conversion efficiency, and fill factor, were almost unaffected. On the other hand, series and shunt resistances of the PV cells derived from numerical fitting of I-V curves were not significantly changed with different treatments. Therefore, no significant impact of substrate treatment on hole collection was concluded, although hole injection under forward bias showed strong dependence on treatment methods. It indicates that hole transfer from CuPc layer to ITO is not the bottleneck in the CuPc/C60 based organic solar cells.
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84.60.Jt Photoelectric conversion

The origin of contrast in the imaging of doped areas in silicon by slow electrons

Luděk Frank, Ilona Müllerová, Dimitrii A. Valdaitsev, Andrei Gloskovskii, Sergei A. Nepijko, Hans-Joachim Elmers, and Gerd Schönhense

J. Appl. Phys. 100, 093712 (2006); http://dx.doi.org/10.1063/1.2364044 (5 pages) | Cited 7 times

Online Publication Date: 10 November 2006

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The importance of high resolution imaging of dopant contrast in semiconductor structures parallels the continuous increase in the degree of their integration and complexity and in the size of substrates. Some scanning electron microscopy modes show moderate contrast between differently doped areas, but its detailed interpretation remains questionable, in particular, as regards the measurement of the dopant concentration. Photoemission spectromicroscopy on silicon substrates with patterns of opposite-type dopants suggests that the p/n contrast is primarily related to local differences in the absorption of hot electrons along their trajectory toward the surface. This explanation is also expected to be valid in the interpretation of image contrasts formed by secondary electrons or very slow backscattered electrons. Wide-field photoemission electron microscopy has proven itself a fast imaging method providing large p-n contrast and the prospect of high-level resolution.
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61.72.S- Impurities in crystals
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Hx Electron impact: secondary emission

Interfacial atomic structures, energetics and band offsets of Ge:ZrO2 interfaces

Koon-Yiu Tse and John Robertson

J. Appl. Phys. 100, 093713 (2006); http://dx.doi.org/10.1063/1.2369645 (9 pages) | Cited 9 times

Online Publication Date: 10 November 2006

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Future field effect transistors may use germanium as a high mobility channel material instead of silicon, and high dielectric constant (κ) oxides such as ZrO2 and HfO2 instead of SiO2 as the gate dielectric. First principles calculations of the polar (100) and nonpolar (110) Ge:ZrO2 interfaces are presented. A number of interface configurations that satisfy the valence bonding requirements are constructed and their relaxed structures, total energies, interface electronic states, and band offsets are calculated. For the polar (100) interfaces, the results are quite similar to those of (100) Si:ZrO2. There are numerous semiconducting O-terminated interfaces. The most stable O-terminated interface for a 1×1 surface unit cell has three coordinated oxygen sites. The interface with a tenfold coordinated Zr is the most stable metal-terminated interface, but it is metallic which makes this interface not useful for devices. The band offsets of the O-terminated interfaces have a relatively narrow range, whereas the Zr-terminated band offsets exhibit a range of 0.9 eV.
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73.20.At Surface states, band structure, electron density of states
77.55.-g Dielectric thin films
71.15.Nc Total energy and cohesive energy calculations
68.35.Ct Interface structure and roughness

Energy level alignment symmetry at Co/pentacene/Co interfaces

M. Popinciuc, H. T. Jonkman, and B. J. van Wees

J. Appl. Phys. 100, 093714 (2006); http://dx.doi.org/10.1063/1.2369651 (8 pages) | Cited 16 times

Online Publication Date: 10 November 2006

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We have employed x-ray and ultraviolet photoemission spectroscopies (XPS and UPS) to study the energy level alignment and electronic structure at the Co/pentacene/Co interfaces. In the case of pentacene deposition on Co we found an interfacial dipole of about 1.05 eV and a hole injection barrier of 0.96 eV, whereas for the case of Co deposition on pentacene we found a similar value for the hole injection barrier and vacuum level alignment ( ∼ 0 eV interfacial dipole), respectively. By combining XPS and UPS we were able to identify that chemical reaction occurs between pentacene and Co. The results of the deposition of the reactive Co on pentacene indicates only a small penetration depth of the metal atoms into the pentacene layer. A complete band diagram for the layered Co/pentacene/Co structure is presented in the frame of a model with interfacial dipoles. Finally, our findings are linked to spin injection experiments.
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73.40.Sx Metal-semiconductor-metal structures
72.25.Mk Spin transport through interfaces
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
82.30.-b Specific chemical reactions; reaction mechanisms

Fermi level pinning in heavily neutron-irradiated GaN

A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, A. V. Markov, N. G. Kolin, D. I. Merkurisov, V. M. Boiko, K. D. Shcherbatchev, V. T. Bublik, M. I. Voronova, I-H. Lee, C. R. Lee, S. J. Pearton, A. Dabirian, and A. V. Osinsky

J. Appl. Phys. 100, 093715 (2006); http://dx.doi.org/10.1063/1.2361157 (4 pages) | Cited 15 times

Online Publication Date: 10 November 2006

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Undoped n-GaN grown by two different metallorganic chemical vapor deposition (MOCVD) techniques, standard MOCVD and epitaxial lateral overgrowth, and Mg-doped p-GaN prepared by hydride vapor phase epitaxy and molecular beam epitaxy were irradiated with fast reactor neutrons to the high fluence of 1018 cm−2. In such heavily irradiated samples the Fermi level is shown to be pinned in a narrow interval of Ec−(0.8−0.95) eV, irrespective of the starting sample properties. The Fermi level pinning position correlates with the measured Schottky barrier height in n-type GaN. The results are interpreted from the standpoint of the existence of the charge neutrality level in heavily disordered material. Based on published theoretical calculations and on deep level transient spectroscopy (measurements and lattice parameter measurements in irradiated material), it is proposed that the Fermi level could be pinned between the gallium-interstitial-related deep donors near Ec−0.8 eV and nitrogen-interstitial-related acceptors near Ec−0.9 eV
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71.55.Eq III-V semiconductors
61.80.Hg Neutron radiation effects
61.82.Fk Semiconductors
61.72.J- Point defects and defect clusters

Determination of capture cross sections for as-grown electron traps in HfO2/HfSiO stacks

C. Z. Zhao, J. F. Zhang, M. B. Zahid, B. Govoreanu, G. Groeseneken, and S. De Gendt

J. Appl. Phys. 100, 093716 (2006); http://dx.doi.org/10.1063/1.2364043 (10 pages) | Cited 15 times

Online Publication Date: 13 November 2006

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A major challenge for replacing gate SiON with HfO2 is the instability and reliability of HfO2. Unlike the SiON, there can be substantial amount of as-grown electron traps in HfO2. These traps can cause instability in the threshold voltage and contribute to the dielectric breakdown. Despite the early efforts, our understanding of them is incomplete. Agreement on their capture cross sections has not been reached and the reported values spread in a large range of 10−12–10−19 cm2. The objective of this paper is to determine their capture cross sections unambiguously, which requires knowing the gate current and the electron fluency for filling the trap. A key part of this work is to estimate the trapping-induced transient gate current following the application of a pulse to the gate. This is achieved by numerical simulation. It is found that trapping can reduce the gate current by two orders of magnitude and the gate current can drop substantially within microseconds. The results show the presence of two distinctive capture cross sections in the order of 10−14 and 10−16 cm2, respectively, which most likely originated from two different types of as-grown electron traps in HfO2. These capture cross sections are insensitive to fabrication and processing techniques.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
77.55.-g Dielectric thin films
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Band gap bowing and electron localization of GaxIn1−xN

Byounghak Lee and Lin Wang Wang

J. Appl. Phys. 100, 093717 (2006); http://dx.doi.org/10.1063/1.2364450 (4 pages) | Cited 16 times

Online Publication Date: 13 November 2006

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The band gap bowing and the electron localization of GaxIn1−xN are calculated using both the local density approximation (LDA) and screened-exchange local density functional (sX-LDA) methods. The calculated sX-LDA band gaps are in good agreement with the experimentally observed values, with errors of −0.26 and 0.09 eV for bulk GaN and InN, respectively. The LDA band gap errors are 1.33 and 0.81 eV for GaN and InN, in order. In contrast to the gap itself, the band gap bowing parameter is found to be very similar in sX-LDA and LDA. We identify the localization of hole states in GaxIn1−xN alloys along In–N–In chains. The predicted localization is stronger in sX-LDA.
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71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Energy band alignment of HfO2 on Ge

M. Perego, G. Seguini, and M. Fanciulli

J. Appl. Phys. 100, 093718 (2006); http://dx.doi.org/10.1063/1.2360388 (4 pages) | Cited 23 times

Online Publication Date: 14 November 2006

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The band alignment of hafnium oxide films grown on Ge (100) by atomic layer deposition has been investigated by x-ray photoelectron spectroscopy (XPS) and internal photoemission (IPE) spectroscopy. HfO2 films have been grown using HfCl4 as hafnium precursor while O3 or H2O have been used as oxygen precursors. The valence-band offset (VBO) values, determined by XPS, are 3.0±0.1 eV and 3.1±0.1 eV for the samples grown using O3 and H2O, respectively. A conduction-band offset (CBO) value of 2.0±0.1 eV has been obtained by IPE for all the samples. Considering a band gap of 5.6±0.1 eV, as obtained by photoconductivity measurements, XPS and IPE results have been found to be in excellent agreement. The CBO and VBO values are the same in all the samples within the experimental error. The presence of a thick GeOx interfacial layer in the samples grown using O3 is not affecting the band alignment of the HfO2/Ge heterojunction.
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71.20.Ps Other inorganic compounds
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
72.40.+w Photoconduction and photovoltaic effects

Characterization of indium tin oxide surfaces and interfaces using low intensity x-ray photoemission spectroscopy

Y. Yi, J. E. Lyon, M. M. Beerbom, and R. Schlaf

J. Appl. Phys. 100, 093719 (2006); http://dx.doi.org/10.1063/1.2361089 (7 pages) | Cited 20 times

Online Publication Date: 15 November 2006

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Ultraviolet photoemission spectroscopic (UPS) and x-ray photoemission spectroscopic (XPS) characterizations of indium tin oxide (ITO) surfaces prepared in ambient environment significantly lower the work function of the ITO surface. This artifact complicates the investigation of ITO surfaces and interfaces using XPS and UPS. The presented results demonstrate that, while the exposure of the sample surface to standard UPS UV sources results in a reduction of the work function within a second or less, XPS measurements show a more gradual work function change over the course of hundreds of seconds. This allowed the design of a measurement protocol based on low intensity x-ray photoelectron spectroscopy work function measurements, which do not cause significant work function changes during the exposure time needed for characterization. Applying this technique, the orbital lineup between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital of the semiconducting polymer poly(3-hexylthiophene) (P3HT) and the valence and conduction bands of ITO were determined. The results indicate that it is appropriate to describe the ITO/P3HT junction as semiconductor heterojunction, and that hole injection most likely occurs between ITO conduction band minimum and P3HT HOMO.
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Fr Polymers; organic compounds
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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