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15 Mar 2007

Volume 101, Issue 6, Articles (06xxxx)

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Electrical characterization of alpha radiation-induced defects in p-GaAs grown by metal-organic chemical-vapor deposition

Nazir A. Naz, Umar S. Qurashi, and M. Zafar Iqbal

J. Appl. Phys. 101, 063701 (2007); http://dx.doi.org/10.1063/1.2710298 (8 pages) | Cited 2 times

Online Publication Date: 16 March 2007

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Investigations of the alpha particle irradiation-induced defects in low-pressure metal-organic chemical-vapor deposition grown p-GaAs have been carried out. By employing deep-level transient spectroscopy, at least seven radiation-induced deep-level defects have been observed in the lower half of the band gap in the temperature range of 12−475 K. Double-correlation deep-level transient spectroscopy measurements show three prominent levels: two known radiation-induced levels namely, Hα1 and Hα5, and one inadvertent center HSA, present before irradiation, to exhibit a significant dependence of thermal emission rate on the junction electric field. For Hα1 and HSA the field-enhanced emission data are well fitted with a Poole-Frenkel model, using a three-dimensional square-well potential with radius r = 3.2 and 1.43 nm, respectively. The field effect for Hα5 has been explained by a square-well potential in combination with a phonon-assisted tunneling process. Detailed data on the carrier capture cross section for all three levels have been obtained. The hole capture cross section for the levels Hα1 and Hα5 are found to be temperature independent, while for HSA, the hole capture data show a dependence on temperature. The dependence of hole capture cross section of HSA on temperature has been explained in terms of multiphonon capture mechanism, yielding a capture barrier of 0.13 eV and σ(∞) = 1.5×10−14 cm2. These analyses lead us to conclude that the levels Hα1 and HSA are associated with a charged center, while the level Hα5 is most likely a substitutional defect in GaAs.
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71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Ht High-field and nonlinear effects
79.70.+q Field emission, ionization, evaporation, and desorption
61.82.Fk Semiconductors

Fabrication and characterization of TiSi2/Si heteronanocrystal metal-oxide-semiconductor memories

Yan Zhu, Bei Li, and Jianlin Liu

J. Appl. Phys. 101, 063702 (2007); http://dx.doi.org/10.1063/1.2710441 (4 pages) | Cited 2 times

Online Publication Date: 19 March 2007

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TiSi2/Si heteronanocrystals on ultrathin oxide was fabricated with self-aligned silicidation method. Compared with Si nanocrystal memory device, TiSi2/Si heteronanocrystal metal-oxide-semiconductor memory device shows higher writing saturation level, faster writing/erasing speed, longer retention, and larger memory window. Therefore, heteronanocrystals are very promising to replace Si nanocrystals for future nonvolatile memory applications.
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85.30.De Semiconductor-device characterization, design, and modeling

Analysis of the size effect in electroplated fine copper wires and a realistic assessment to model copper resistivity

W. Zhang, S. H. Brongersma, Z. Li, D. Li, O. Richard, and K. Maex

J. Appl. Phys. 101, 063703 (2007); http://dx.doi.org/10.1063/1.2711385 (11 pages) | Cited 14 times

Online Publication Date: 20 March 2007

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The size effect in electroplated copper wires has been widely studied recently. However, there is no consensus on the role of various scattering mechanisms. Therefore, an in-depth analysis to reveal the origin of the size effect is needed. In this article, we study the resistivity of fine copper wires whose feature sizes shrink in two dimensions. It is shown that the residual resistivity (at 5 K) increases with decreasing wire width or height and the temperature-dependent resistivity slightly deviates from that of bulk copper. This is mainly attributed to surface scattering rather than grain boundary scattering. In fact, the influence of grain boundary scattering in these well annealed copper wires is relatively small. In addition, for copper wires with a constant height, a linear dependence of the copper resistivity on 1/width (w) or 1/cross-sectional area (A), namely ρ = ρic+c*/w (or ρ = ρic+c**/A), is derived from the classic surface and grain boundary scattering models and validated experimentally. In this simple description, the contributions of different scattering mechanisms, such as surface reflectivity, p, and grain boundary reflection coefficient, R, defect and impurity density, combine together in parameters of ρic and c* (or c**). Especially, c* is a good indicator of scattering strength, from which one can quantitatively analyze the impact of nonsurface scattering contribution with a reference slope of c* = 32.14.
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73.63.Nm Quantum wires
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
73.25.+i Surface conductivity and carrier phenomena
61.46.-w Structure of nanoscale materials
61.72.Mm Grain and twin boundaries

A possible realization of spin filter using a quantum wire with Rashba spin-orbit coupling

Genhua Liu and Guanghui Zhou

J. Appl. Phys. 101, 063704 (2007); http://dx.doi.org/10.1063/1.2512392 (4 pages) | Cited 10 times

Online Publication Date: 21 March 2007

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We study theoretically the spin-polarized electron transport properties for a weak Rashba spin-orbit coupling (SOC) quantum wire connected nonadiabatically to two normal-conductor electrode leads. The influence of both the mode mixing due to wire-lead connection and Rashba SOC split on the spin-polarized electron transport is treated simultaneously by means of scattering matrix within the framework of effective free-electron approximation. The analytical analysis with numerical examples demonstrates that the purely spin-polarized current can occur for the system with an appropriate system geometry and material parameters. Our result may imply a simple approach to the design of a spin filter device without containing any magnetic materials or applying a magnetic field.
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72.25.-b Spin polarized transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Improved near-infrared transparency in sputtered In2O3-based transparent conductive oxide thin films by Zr-doping

T. Koida and M. Kondo

J. Appl. Phys. 101, 063705 (2007); http://dx.doi.org/10.1063/1.2711768 (4 pages) | Cited 9 times

Online Publication Date: 23 March 2007

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Transparent conductive Zr-doped In2O3 (In2−2xZr2xO3) films were deposited on glasses by sputtering method. High mobility of over 80 cm2/V s was achieved under a carrier density of 1.3−2.9×1020 cm−3 at Zr concentrations (x) of 0.014–0.022, and the film at x = 0.022 showed the lowest resistivity of 2.6×10−4 Ω cm. Reflecting the high mobility and the low carrier density, the transparency extended from the visible to the near-infrared (NIR) wavelength region with reduced magnitude of the free-carrier absorption. The results indicate that Zr-doped In2O3 films have a performance advantage for applications that require high conductivity and transparency in NIR wavelength region.
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78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.61.Le Other inorganic semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
42.70.Km Infrared transmitting materials

The electronic structure of ultrathin aluminum oxide film grown on FeAl(110): A photoemission spectroscopy

O. Kizilkaya, I. C. Senevirathne, and P. T. Sprunger

J. Appl. Phys. 101, 063706 (2007); http://dx.doi.org/10.1063/1.2710305 (5 pages) | Cited 2 times

Online Publication Date: 23 March 2007

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The electronic structure of the ultrathin aluminum oxide grown on the FeAl(110) surface has been investigated with angle-resolved photoemission spectroscopy. Previous scanning tunneling microscopy studies have revealed that exposing the clean FeAl(110) surface to 1000 l of oxygen at 850 °C forms a homogeneous hexagonal oxide film with a thickness of approximately 10 Å. Core level photoemission spectra of FeAl constituents indicate that Al is the only metal species present in the oxide film. The measured band dispersion of the oxide thin film indicates a two dimensional electronic structure parallel to the plane of the thin film due to the limited thickness of the oxide thin films. The appearance of a peak in the anticipated band gap of the bulk oxide film suggests a unique electronic structure of the two dimensional oxide film. This latter observation is correlated with previous scanning tunneling microscopy results to elucidate the structure of the ultrathin alumina film grown on FeAl(110).
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71.20.Ps Other inorganic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

The wave function evolution of an exciton in a bilayer system: Turning on a static in-plane electric field

Li Wang

J. Appl. Phys. 101, 063707 (2007); http://dx.doi.org/10.1063/1.2437692 (4 pages)

Online Publication Date: 26 March 2007

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The time evolution of the ground state wave function of an exciton in an ideal bilayer system is investigated within the framework of the effective-mass approximation. All of the moduli squared of the ground state wave functions evolve with time as cosine functions after an in-plane electric field is applied to the bilayer system. The variation amplitude and period of the modulus squared of the ground state wave function increase with the in-plane electric field Fr for a fixed in-plane relative coordinate r and fixed separation d between the electron and hole layers. Moreover, the variation amplitude and period of the modulus squared of the ground state wave function increase with the separation d for a fixed r and fixed in-plane electric field. Additionally, the modulus squared of the ground state wave function decreases as r increases at a given time t for fixed values of d and Fr.
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71.35.-y Excitons and related phenomena

Thermal stability of nitrogen-doped SrTiO3 films: Electronic and optical properties studies

Y. Y. Mi, Z. Yu, S. J. Wang, X. Y. Gao, A. T. S. Wee, C. K. Ong, and C. H. A. Huan

J. Appl. Phys. 101, 063708 (2007); http://dx.doi.org/10.1063/1.2713350 (5 pages) | Cited 3 times

Online Publication Date: 26 March 2007

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The thermal stability of nitrogen-doped SrTiO3 (001) films in terms of electronic and optical properties has been studied by using x-ray photoemission spectroscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry techniques. The chemical states of nitrogen in nitrogen-doped SrTiO3 films include both substitutional and interstitial states. The N 2p states localized above the O 2p-derived valence band maximum are attributed to the change of optical properties. Postannealing will induce the valence band edge shift due to the thermal instability of interstitial N states, which may degrade the photocatalysis of nitrogen-doped SrTiO3 films during applications.
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68.60.Dv Thermal stability; thermal effects
73.20.At Surface states, band structure, electron density of states
78.66.Nk Insulators
79.60.Dp Adsorbed layers and thin films
78.70.Dm X-ray absorption spectra
82.50.Hp Processes caused by visible and UV light

Ambipolar charge carrier transport in mixed organic layers of phthalocyanine and fullerene

Andreas Opitz, Markus Bronner, and Wolfgang Brütting

J. Appl. Phys. 101, 063709 (2007); http://dx.doi.org/10.1063/1.2436836 (9 pages) | Cited 33 times

Online Publication Date: 27 March 2007

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Mixed layers of copper-phthalocyanine (p-conductive) and fullerene (n-conductive) are used for the fabrication of organic field-effect transistors (OFET) and inverters. Regarding the electrical characteristics of these donor-acceptor blends they show ambipolar charge carrier transport, whereas devices made from only one of the materials show unipolar behavior. Such mixed films are model systems for ambipolar transport with adjustable field-effect mobilities for electrons and holes. By variation of the mixing ratio it is possible to balance the transport of both charge-carrier types. In this paper we discuss the variation of mobility and threshold voltage with the mixing ratio and demonstrate ambipolar inverters as a leadoff application. The gained results were analyzed by simulations using an analytical model for ambipolar transistors and subsequently compared to complementary inverters.
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85.30.Tv Field effect devices
85.30.Pq Bipolar transistors
85.65.+h Molecular electronic devices
84.30.Jc Power electronics; power supply circuits

Analytical expressions for the conductance noise measured with four circular contacts placed in a square array

G. Leroy, J. Gest, L. K. J. Vandamme, and A. P. J. van Deursen

J. Appl. Phys. 101, 063710 (2007); http://dx.doi.org/10.1063/1.2434942 (9 pages) | Cited 1 time

Online Publication Date: 28 March 2007

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In the ideal case, noise measurements with four contacts minimize the contribution of the contact interface. There is a need to characterize conductance noise and noise correction factors for the different geometries provided with four contacts, as already is the case for resistivity measurements with van der Pauw structures. Here, we calculate the noise correction factors for two geometries with a pair of sensors and a pair of current driver electrodes placed in a square array. The first geometry investigated is a very large film compared to the distance L between four circular electrodes, which are placed in a square array far away from the borders of the film. The second is a square-shaped conductive film with side length L and provided with four quarter-circle corner contacts with radius l. The effect of the conductance noise in the film can be observed between current free sensors in a four-point measurement or between current carrying drivers in a two-point measurement. Our analytical expressions are based on approximations to solve the integrals ∬(J∙math)2dA and ∬∣J∣4dA for the voltage noise measured across a pair of sensors, SVQ, and across the drivers, SVD, respectively. The first and second integrands represent the squared dot product of the current density and adjoint current density and the modulus of the current density to the fourth power, respectively. The current density J in the samples is due to the current I passing through the driver contacts. The calculated expressions are applicable to samples with thickness t⪡l ⩽ 0.1L. Hence, the disturbances in the neighborhood of the sensors on J and of the drivers on math are ignored. Noise correction factors for two- and four-point measurements are calculated for sensors on an equipotential (transversal noise) with the driver contacts on the diagonal of a square and for sensors next to each other on one side of the square with the drivers next to each other on the other side of the square (longitudinal noise). In all cases the noise between the sensors is smaller and less sensitive to the contact size 2l/L than the noise between the drivers. The ratio SVQ/SVD becomes smaller with smaller contact radius l. Smaller sensors give a better suppression of interface noise at the contacts. But overly low 2l/L values result in overly high resistance between the sensors and too strong a contribution of thermal noise at the sensors. Therefore, equations are derived to calculate the current level needed to observe 1/f conductance fluctuations on top of the thermal noise. The results from the calculated analytical expressions show good agreement with experimental results obtained from the noise in carbon sheet resistance and numerical results. Transversal noise measurements on a square sample with corner contacts are recommended to characterize the 1/f noise of the layer. This is due to the increased current densities in the sample compared to the open structure, which result in easier detection of the 1/f on top of the thermal noise.
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73.61.-r Electrical properties of specific thin films
73.50.Td Noise processes and phenomena
73.40.-c Electronic transport in interface structures
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Mapping of polarization and detrapping effects in synthetic single crystal chemical vapor deposited diamond by ion beam induced charge imaging

A. Lohstroh, P. J. Sellin, S. G. Wang, A. W. Davies, and J. M. Parkin

J. Appl. Phys. 101, 063711 (2007); http://dx.doi.org/10.1063/1.2653669 (7 pages) | Cited 5 times

Online Publication Date: 28 March 2007

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Diamond has been regarded as a promising radiation detector material for use as a solid state ionizing chamber for decades. The parameters degrading the charge transport from what is expected from an ideal crystal are still not completely understood. Recently, synthetic chemical vapor deposited (CVD) single crystal diamond has become available, offering the opportunity to study the properties of synthesized material independent of grain boundaries. We have studied the charge transport of a synthetic single crystal diamond with α-particle induced charge transients as a function of temperature and established the presence of a shallow hole trap with an activation energy of 0.29±0.02 eV in some parts of the detector. Ion beam induced charge imaging has been used to study the spatial variations of the charge transport in a synthetic single crystal diamond. Pulses influenced by the shallow hole trap had their origin close to the substrate∕CVD interface of the sample. They could be clearly distinguished from pulses affected by reduced charge carrier velocities due to polarization phenomena, which varied systematically with the growth direction of the CVD diamond material.
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72.80.Cw Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Mm Grain and twin boundaries
71.55.Cn Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Radiative emission from multiphoton-excited semiconductor quantum dots

T.-T. Han, Y. Fu, and H. Ågren

J. Appl. Phys. 101, 063712 (2007); http://dx.doi.org/10.1063/1.2715811 (6 pages) | Cited 1 time

Online Publication Date: 29 March 2007

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Optical transitions in CdS semiconductor quantum dots (QDs) have been studied by the Monte Carlo method based on probability calculations of the time-dependent Schrödinger equation. It has been demonstrated that excited by a continuous-wave laser, an assembly of CdS QDs, whose radii range from 2 to 5 nm centered at 3.7 nm, shows an emission peak around 2.65 eV in the optical emission spectrum, which corresponds to optical transitions among degenerate sublevels close to the ground sublevels in the conduction and valence bands of a CdS QD having a radius of 3.7 nm. For resonant one-photon excitation, the emission peak is very sharp, while for resonant two-photon excitation, the emission peak becomes blueshifted and broadened. The inclusion of the nonradiative electron-phonon processes makes the two-photon excitation peak significantly sharper and shows a better agreement with experimental work, thus demonstrating the upconversion luminescence of the QDs required for many applications including bioimaging.
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73.22.-f Electronic structure of nanoscale materials and related systems
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.07.Ta Quantum dots
78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Et II-VI semiconductors

Comparative studies of transparent conductive Ti-, Zr-, and Sn-doped In2O3 using a combinatorial approach

T. Koida and M. Kondo

J. Appl. Phys. 101, 063713 (2007); http://dx.doi.org/10.1063/1.2712161 (6 pages) | Cited 11 times

Online Publication Date: 29 March 2007

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We report on comparative studies of transparent conductive Ti-, Zr-, and Sn-doped In2O3 using a combinatorial approach. In2−2xMe2xO3 (Me:Ti, Zr, Sn) composition-spread epilayers (0 ≤ x ≤ 0.1) were fabricated on yttria-stabilized zirconia substrates using the combinatorial pulsed laser deposition technique, and structural, optical, and electrical properties for each composition were systematically investigated. In2−2xTi2xO3 (0.003 ≤ x<0.01) and In2−2xZr2xO3 (0.003 ≤ x<0.05) exhibited superior transparency in the near infrared wavelength region compared to In2−2xSn2xO3 without compromising the conductivity. The results are discussed in terms of scattering centers of electrons from temperature dependence of Hall mobility and the relationship between the values of the room temperature Hall mobility and carrier concentration.
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68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
73.61.Le Other inorganic semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Geometrical-confinement effects on two electrons in elliptical quantum dots

Yong-Hui Liu, Fu-Hua Yang, and Song-Lin Feng

J. Appl. Phys. 101, 063714 (2007); http://dx.doi.org/10.1063/1.2712160 (4 pages)

Online Publication Date: 29 March 2007

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The effects of the geometrical shape on two electrons confined in a two-dimensional parabolic quantum dot and subjected to an external uniform magnetic field have been calculated using a variational-perturbation method based on a direct construction of trial wave functions. The calculations show that both the energy levels and the spin transition of two electrons in elliptical quantum dots are dramatically influenced by the shape of the dots. The ground states with total spin S = 0 and S = 1 are affected greatly by changing the magnetic field and the geometrical confinement. The quantum behavior of elliptical quantum dots show some relation to that of laterally coupled quantum dots. For a special geometric configuration of the confinement ωy/ωx = 2.0, we encounter a characteristic magnetic field at which spin singlet-triplet crossover occurs.
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73.21.La Quantum dots
71.15.-m Methods of electronic structure calculations

Resistance maps from local probing of a ballistic mesoscopic Hall bar

G. Papp and F. M. Peeters

J. Appl. Phys. 101, 063715 (2007); http://dx.doi.org/10.1063/1.2713365 (4 pages) | Cited 4 times

Online Publication Date: 30 March 2007

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The response of a ballistic mesoscopic Hall bar to a local potential barrier is investigated in the presence of an external magnetic field. The effect of the position of the local potential probe in the Hall cross on the Hall and bend resistance is investigated leading to two-dimensional (2D) resistance maps. The Onsager–Casimir symmetry relations and symmetry relations between resistance measurements when interchanging the current and voltage leads, is obtained numerically for such 2D resistance maps. Symmetry properties are derived for the Hall and bend resistance maps with respect to the position of the local potential barrier.
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73.23.Ad Ballistic transport
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