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15 Feb 2012

Volume 111, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 043501 (2012); http://dx.doi.org/10.1063/1.3680881 (8 pages)

Gregory J. McGraw and Stephen R. Forrest
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back to top Electronic Structure and Transport

Impact of incomplete ionization of dopants on the electrical properties of compensated p-type silicon

M. Forster, A. Cuevas, E. Fourmond, F. E. Rougieux, and M. Lemiti

J. Appl. Phys. 111, 043701 (2012); http://dx.doi.org/10.1063/1.3686151 (7 pages) | Cited 2 times

Online Publication Date: 17 February 2012

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This paper investigates the importance of incomplete ionization of dopants in compensated p-type Si and its impact on the majority-carrier density and mobility and thus on the resistivity. Both theoretical calculations and temperature-dependent Hall-effect measurements demonstrate that the carrier density is more strongly affected by incomplete ionization in compensated Si than in uncompensated Si with the same net doping. The previously suggested existence of a compensation-specific scattering mechanism to explain the reduction of mobility in compensated Si is shown not to be consistent with the T-dependence of the measured carrier mobility. The experiment also shows that, in the vicinity of 300 K, the resistivity of compensated Si has a much weaker dependence on temperature than that of uncompensated silicon.
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61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects

First-principles study on electronic structures and magnetic properties of AlN nanosheets and nanoribbons

Chang-wen Zhang

J. Appl. Phys. 111, 043702 (2012); http://dx.doi.org/10.1063/1.3686144 (6 pages) | Cited 1 time

Online Publication Date: 21 February 2012

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Based on first-principles calculations, the effects of the intrinsic defects and edge states on electronic structures and magnetic properties of AlN nanosheets (NSs) and nanoribbons (NRs) are investigated. In comparison to Al-defective AlN NS, N-defective systems can be easily achieved in experiments, and show a ferromagnetic (FM) property with Curie temperatures above room temperature. For quasi one-dimensional (1D) single-layer zigzag (ZZ) and armchair (AC) AlNNRs with and without edge atoms passivated by hydrogen, the bare and H-passivated AC and ZZNRs are found to be nonmagnetic (NM) semiconductors, whereas a FM character occurs in bare ZZNRs. We also find that the bandgap in H-passivated NRs decreases with the increase of the width of NRs, while bandgap in bare ACNRs increases with increasing the ribbon width. More interesting, in the case of multilayer ZZNRs, when the number of Al-N layers are even, they show NM semiconducting characters, while the odd-layer ZZNRs exhibit magnetic behaviors. Our predicted diverse and tunable electronic and magnetic properties endow AlN nanostructures potential applications in electronics and spintronics.
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71.20.Nr Semiconductor compounds
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Lf Electronic structure of magnetic nanoparticles
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors

Modeling metastabilities in chalcopyrite-based thin film solar cells

Koen Decock, Paweł Zabierowski, and Marc Burgelman

J. Appl. Phys. 111, 043703 (2012); http://dx.doi.org/10.1063/1.3686651 (7 pages) | Cited 3 times

Online Publication Date: 21 February 2012

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Cu(In,Ga)Se2-based thin film solar cell devices exhibit metastable electrical behavior. This behavior is often ascribed to intrinsic defects that can change configuration accompanied by large lattice relaxations. We extended the thin film solar cell simulation software scaps to enable the simulation of the metastable behavior of this kind of defects. The statistics that are needed to describe metastable defects are discussed. The procedure that has been implemented is introduced, and special attention is paid to the convergence of the method for high defect densities. The model is demonstrated by simulating the effect of voltage induced metastabilities on the capacitance-voltage characteristics. Some of the features present in the measured apparent doping density profiles can be directly related to presence of metastable defects.
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88.40.jn Thin film Cu-based I-III-VI2 solar cells
73.61.Le Other inorganic semiconductors
61.72.up Other materials

Thermoelectric properties of Zn-doped GaSb

Chang-eun Kim, Ken Kurosaki, Hiroaki Muta, Yuji Ohishi, and Shinsuke Yamanaka

J. Appl. Phys. 111, 043704 (2012); http://dx.doi.org/10.1063/1.3678012 (3 pages)

Online Publication Date: 22 February 2012

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III-V compounds with the zinc blende structure have good power factors due to their high carrier mobility. In the present study, Zn-doped GaSb (Ga1−xZnxSb, x = 0.001, 0.002, 0.005, and 0.01) samples were fabricated and the thermoelectric (TE) properties of the samples were measured. Hall measurements were conducted to investigate the carrier transport properties and the results revealed a highest power factor of 2.02 W/m K2 for the sample with x = 0.002 at 573 K, of which the largest weighted mobility was also obtained. However, Zn-doped GaSb also exhibits high thermal conductivity (24.3 W/m K for the sample with x = 0.002 at room temperature). The maximum TE efficiency of 0.23 was obtained at 873 K for the sample with x = 0.01.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Ey III-V and II-VI semiconductors
66.70.Df Metals, alloys, and semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects

Influence of Cu column under-bump-metallizations on current crowding and Joule heating effects of electromigration in flip-chip solder joints

Y. C. Liang, W. A. Tsao, Chih Chen, Da-Jeng Yao, Annie T. Huang, and Yi-Shao Lai

J. Appl. Phys. 111, 043705 (2012); http://dx.doi.org/10.1063/1.3682484 (7 pages) | Cited 2 times

Online Publication Date: 22 February 2012

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The electromigration behavior of SnAg solder bumps with and without Cu column under-bump-metallizations (UBMs) has been investigated under a current density of 2.16 × 104 A/cm2 at 150 °C. Different failure modes were observed for the two types of samples. In those without Cu column UBMs, when SnAg solder bumps that had implemented 2 μm Ni UBMs were current stressed at 2.16 × 104 A/cm2, open failure occurred in the bump that had an electron flow direction from the chip side to the substrate side. However, in those with Cu column UBMs, cracks formed along the interface of Cu6Sn5 intermetallic compounds and the solder on the substrate side in the Sn-3.0Ag–0.5Cu solder bump that had an electron flow direction from the substrate side to the chip side. A three-dimensional simulation of the current density distribution was performed in order to obtain a better understanding of the current crowding behavior in solder bumps. The current crowding effect was found to account for the void formation on both the chip and the substrate side for the two kinds of solder bumps. One more important finding, as confirmed by infrared microscopy, is that the alleviation of current crowding by Cu column UBMs also helped decrease the Joule heating effect in solder bumps during current stressing. Therefore, the measured failure time for the solder joints with Cu column UBMs appears to be much longer than that of the ones with the 2 μm Ni UBMs.
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66.30.Qa Electromigration
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks
61.72.Qq Microscopic defects (voids, inclusions, etc.)

High temperature thermoelectric properties of the type-I clathrate Ba8AuxSi46−x

C. Candolfi, U. Aydemir, M. Baitinger, N. Oeschler, F. Steglich, and Yu . Grin

J. Appl. Phys. 111, 043706 (2012); http://dx.doi.org/10.1063/1.3682585 (7 pages)

Online Publication Date: 22 February 2012

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The thermoelectric properties of the type-I clathrate Ba8AuxSi46−x (4.10 ≤ x ≤ 6.10) were characterized from 300 to 700 K. Increasing the Au concentration leads to a transition from an n-type (x < 5.43) to a p-type (x ≥ 5.43) electrical conduction. The experimental data are well described by a single-parabolic-band model assuming a single scattering mechanism of the charge carriers in this temperature range. The lattice thermal conductivity, inferred from degeneracy-adjusted Lorenz numbers, is low regardless of the composition. However, the measured values are significantly lower in the p-type samples possibly due to a combination of a higher degree of disorder in the crystal structure at high Au contents and an enhanced phonon-charge carrier coupling. Even though high thermopower values are achieved, the high electrical resistivity remains the main obstacle to push the dimensionless figure of merit ZT (∼0.2 at around 600 K for x = 5.59) beyond the level of the best Si-based clathrate compounds.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.60.+g Mixed conductivity and conductivity transitions
72.80.Sk Insulators
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
61.66.Fn Inorganic compounds

The impact of Ge codoping on the enhancement of photovoltaic characteristics of B-doped Czochralski grown Si crystal

Mukannan Arivanandhan, Raira Gotoh, Tatsuro Watahiki, Kozo Fujiwara, Yasuhiro Hayakawa, Satoshi Uda, and Makoto Konagai

J. Appl. Phys. 111, 043707 (2012); http://dx.doi.org/10.1063/1.3687935 (6 pages) | Cited 1 time

Online Publication Date: 23 February 2012

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The effect of Ge codoping on minority carrier lifetime in boron (B)-doped Czochralski-silicon (CZ-Si) crystals was investigated. The minority carrier lifetime increased from 110 to 176 µs as Ge concentration was increased from zero to 1 × 1020 cm−3 in B/Ge codoped CZ-Si crystals. Light-induced degradation (LID) experiments showed that B-doped CZ-Si degrades rapidly, while B/Ge codoped CZ-Si degrades more slowly. Moreover, the flow pattern defect (FPD) density of grown-in micro-defects (GMD) in as-grown B/Ge codoped CZ-Si decreased with increasing Ge concentration. From the infrared (IR) absorption studies, it was observed that the interstitial oxygen (Oi) concentration decreased as Ge concentration increased in the crystal. The suppressed LID effect in the B/Ge codoped CZ-Si appears to be related to the low concentration of B-O associated defects, possibly because Ge doping retards the Oi diffusion in addition to the low Oi concentration present (evidenced from IR studies). The mechanism by which the Ge concentration influences the reduction of FPDs and Oi concentration is discussed in terms of Ge-vacancy defect formation during post-growth cooling of the ingots.
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61.72.uf Ge and Si
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.jj Interstitials
61.72.jd Vacancies
81.10.Fq Growth from melts; zone melting and refining
72.40.+w Photoconduction and photovoltaic effects

Epitaxial Ag(001) grown on MgO(001) and TiN(001): Twinning, surface morphology, and electron surface scattering

J. S. Chawla and D. Gall

J. Appl. Phys. 111, 043708 (2012); http://dx.doi.org/10.1063/1.3684976 (10 pages) | Cited 1 time

Online Publication Date: 23 February 2012

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Epitaxial Ag(001) layers were deposited on MgO(001) in order to study electron surface scattering. X-ray reflection indicates 3D layer nucleation with a high rms surface roughness of 1.0 nm for a layer thickness d = 3.5 nm. X-ray diffraction shows that {111} twins form at d < 11 nm, followed by 2nd generation twinning for 11 nm < d < 120 nm. Increasing the growth temperature from 25 to 150 °C suppresses 2nd generation twinning and reduces the twin density by 2 orders of magnitude. In situ deposition of epitaxial 2.5-nm-thick TiN(001) underlayers prior to Ag deposition results in twin-free single-crystal Ag(001) with 10 × smoother surfaces for d = 3.5 nm. This is attributed to a better wetting on the higher energy TiN(001) than MgO(001) surface, resulting in the absence of 3D nuclei with exposed {111} facets, which facilitate twin nucleation. The twinned Ag/MgO layers have a higher resistivity ρ than the single crystal Ag/TiN layers at both 298 and 77 K, due to electron scattering at grain and twin boundaries. The ρ for single-crystal Ag layers increases with decreasing d, which is well explained with known surface scattering models and provides specularity parameters for the Ag-vacuum and the Ag-air interfaces of p = 0.8 ± 0.1 and 0.4 ± 0.1, respectively. A comparison with corresponding epitaxial Cu(001) layers shows that ρAg < ρCu for d > 50 nm, consistent with known bulk values. However, ρAg > ρCu for d < 40 nm. This is attributed to the larger electron mean free path for electron-phonon scattering and a correspondingly higher resistivity contribution from surface scattering in Ag than Cu. In contrast, air exposure causes ρAg < ρCu for all d, due to diffuse scattering at the oxidized Cu surface and the correspondingly higher Cu resistivity.
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73.61.At Metal and metallic alloys
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.at Other materials
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
61.72.Mm Grain and twin boundaries
81.05.Bx Metals, semimetals, and alloys
68.55.-a Thin film structure and morphology

Thermoelectric prospects of nanomaterials with spin-orbit surface bands

T. E. Huber, K. Owusu, S. Johnson, A. Nikolaeva, L. Konopko, R. C. Johnson, and M. J. Graf

J. Appl. Phys. 111, 043709 (2012); http://dx.doi.org/10.1063/1.3686206 (5 pages)

Online Publication Date: 23 February 2012

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Nanostructured composites and nanowire arrays of traditional thermoelectrics, like Bi, Bi1-xSbx, and Bi2Te3, have metallic Rashba surface spin-orbit bands featuring high mobilities rivaling that of the bulk for which topological insulator behavior has been proposed. Nearly pure surface electronic transport has been observed at low temperatures in Bi nanowires, with diameter around the critical diameter, 50 nm, for the semimetal-to-semiconductor transition. The surface contributes strongly to the thermopower, actually dominating for temperatures T < 100 K in these nanowires. The surface thermopower was found to be –1 T μV/K2, a value that is consistent with theory. We show that surface electronic transport together with boundary phonon scattering leads to enhanced thermoelectric performance at low temperatures of Bi nanowire arrays. We compare with bulk n-BiSb alloys, optimized CsBi4Te6, and optimized Bi2Te3. Surface dominated electronic transport can be expected in nanomaterials of the other traditional thermoelectrics.
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72.15.Jf Thermoelectric and thermomagnetic effects
73.25.+i Surface conductivity and carrier phenomena
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Charge transport in amorphous low bandgap conjugated polymer/fullerene films

Jung Yong Kim, Hyunduck Cho, Seunguk Noh, Yoonkyoo Lee, Young Min Nam, Changhee Lee, and Won Ho Jo

J. Appl. Phys. 111, 043710 (2012); http://dx.doi.org/10.1063/1.3686633 (7 pages)

Online Publication Date: 23 February 2012

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The structural and charge transport properties of a low bandgap copolymer poly(3-hexylthiophene -alt-6,7-dimethyl-4,9-bis-(4-hexylthien-2yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) (P(3HT-MeTDQ)) and its blend with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are investigated. Thermal analysis, X-ray scattering diffraction (XRD), atomic force microscopy and transmission electron microscopy (TEM) of P(3HT-MeTDQ) reveal that the polymer is amorphous in solid state. As the hole mobility of P(3HT-MeTDQ) was measured by the time-of-flight photoconductivity method, the mobility was 3.35 × 10−4 cm2/V s, which is very comparable to that of semicrystalline poly(3-hexyl thiophene). When the mobility of amorphous P(3HT-MeTDQ) was analyzed according to the Gaussian disorder model, the polymer has the energetic and positional disorders with the values of σ = 62 meV and Σ = 1.7, respectively, indicating that the polymer has a relatively narrow Gaussian distribution of transport states. Interestingly, when P(3HT-MeTDQ) is blended with PCBM, the amorphous P(3HT-MeTDQ) becomes partially ordered, as evidenced by observation of two discernible XRD peaks at 2θ = 5° (d = 17.7 Å) and 25.5° (d = 3.5 Å) corresponding to the interchain distance and π-stacking distance, respectively. The bicontinuous network morphology was identified at the blend with 60 wt. % PCBM by TEM, at which the charge carrier transport changes from hole-only to ambipolar.
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73.40.-c Electronic transport in interface structures
73.61.Ng Insulators
61.41.+e Polymers, elastomers, and plastics
78.70.Ck X-ray scattering
73.50.Dn Low-field transport and mobility; piezoresistance
78.56.-a Photoconduction and photovoltaic effects

Single-particle tunneling in doped graphene-insulator-graphene junctions

R. M. Feenstra, Debdeep Jena, and Gong Gu

J. Appl. Phys. 111, 043711 (2012); http://dx.doi.org/10.1063/1.3686639 (10 pages) | Cited 5 times

Online Publication Date: 23 February 2012

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The characteristics of tunnel junctions formed between n- and p-doped graphene are investigated theoretically. The single-particle tunnel current that flows between the two-dimensional electronic states of the graphene (2D–2D tunneling) is evaluated. At a voltage bias such that the Dirac points of the two electrodes are aligned, a large resonant current peak is produced. The magnitude and width of this peak are computed, and its use for devices is discussed. The influences of both rotational alignment of the graphene electrodes and structural perfection of the graphene are also discussed.
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73.22.Pr Electronic structure of graphene
73.40.Gk Tunneling
73.23.Hk Coulomb blockade; single-electron tunneling
73.63.-b Electronic transport in nanoscale materials and structures

The reduction of effective doping with extra dopant: n-Type doping of tris(8-hydroxyquinoline) aluminum with K

Hyunbok Lee, Sang Wan Cho, Jeihyun Lee, Pyung Eun Jeon, Kwangho Jeong, Jin Woo Lee, and Yeonjin Yi

J. Appl. Phys. 111, 043712 (2012); http://dx.doi.org/10.1063/1.3686704 (5 pages) | Cited 2 times

Online Publication Date: 23 February 2012

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We studied the n-type doping effect of K deposited on tris(8-hydroxyquinoline) aluminum (Alq3), which has been used for efficient organic semiconducting devices for the last decade. The K doped or inserted at the interface region of the Alq3/cathode has shown highly enhanced device characteristics and yet, peculiarly, extra doping of K has always deteriorated the device properties. We study the interfacial electronic structures of the Alq3–K system using in situ photoemission spectroscopy and a theoretical model to understand the origin of such deterioration. As the K doping progresses, the lowest unoccupied molecular orbital (LUMO) of pristine Alq3 is gradually filled and it becomes an occupied gap state. This reduction of LUMO density of states makes the electron injection diminished, which is the origin of the device deterioration.
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61.72.U- Doping and impurity implantation
81.05.Fb Organic semiconductors
82.30.-b Specific chemical reactions; reaction mechanisms
82.45.Fk Electrodes
79.60.-i Photoemission and photoelectron spectra
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Spin-filtering and switching effects of a single-molecule magnet Mn(dmit)2

Yipeng An and Zhongqin Yang

J. Appl. Phys. 111, 043713 (2012); http://dx.doi.org/10.1063/1.3686722 (6 pages) | Cited 1 time

Online Publication Date: 23 February 2012

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We investigated spin-dependent transport properties of a single-molecule magnet Mn(dmit)2 with a coplanar or perpendicular conformation using first-principles density functional theory combined with nonequilibrium Green’s function method. It was found that the current flowing through the junction comprised of two Au leads and a Mn(dmit)2 molecule is high spin-polarized, up to a high efficiency of 82%, if the two ligands of the molecule are orientated in the same plane. The current is strongly suppressed when a ligand is rotated and perpendicular to the other. These results suggest that Mn(dmit)2 is a potential candidate for spin filters or molecular switches.
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72.25.-b Spin polarized transport
75.50.Xx Molecular magnets
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.76.+j Spin transport effects

Lateral in-plane coupling between graphene nanoribbons: A density functional study

Jianhua Zhao, Xianqi Dai, Yawei Dai, Bao Zhao, and Maohai Xie

J. Appl. Phys. 111, 043714 (2012); http://dx.doi.org/10.1063/1.3686673 (6 pages)

Online Publication Date: 27 February 2012

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Properties brought about by lateral in-plane coupling between graphene nanoribbons (GNRs) are investigated using the first-principle total energy calculations. It is found that, when two GNRs approach each other, the lateral coupling between the two brings about edge state splitting. Between zigzag-edged graphene nanoribbons (ZGNRs), the coupling mainly results from Coulomb and spin-spin interaction, while for armchair-edged graphene nanoribbons (AGNRs), it is from Coulomb interaction only. It is further found that the maximum inter-ribbon distance for effective coupling depends on the type of ribbons, which is ∼10 Å for ZGNRs, but ∼6 Å for AGNRs. Also, displacements of the GNRs along the ribbon direction are found to affect the electronic properties of the coupled GNRs. The results may be important for the microminiaturization of future nanoelectronic and spintronic devices based on graphene.
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73.22.Pr Electronic structure of graphene
71.45.Lr Charge-density-wave systems
75.30.Ds Spin waves
71.15.Nc Total energy and cohesive energy calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.75.Lf Electronic structure of magnetic nanoparticles

Polarization engineered 1-dimensional electron gas arrays

Digbijoy N. Nath, Pil Sung Park, Michele Esposto, David Brown, Stacia Keller, Umesh K. Mishra, and Siddharth Rajan

J. Appl. Phys. 111, 043715 (2012); http://dx.doi.org/10.1063/1.3687938 (7 pages) | Cited 1 time

Online Publication Date: 27 February 2012

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Show Abstract
One-dimensional electron gas based devices are of great interest due to their promise in high-performance electronics and future device applications. However, synthesis and patterning of arrays of nanowires is a challenge in all material systems. Here we demonstrate a novel system based on vicinal AlGaN/GaN heterostructures that enables direct electrostatic tuning of the dimensionality of electrons from 1 D to 2 D. Our approach, based on polarization engineering, enables top-down fabrication of dense arrays of pure 1-dimensional electron channels with carrier confinement equivalent to 90 meV, that are capable of carrying technologically relevant current densities up to 130 mA/mm. A direction-dependent small-signal capacitance-voltage profiling to probe the Fermi occupation function of electron gas was used to demonstrate distinct signatures of 1-dimensional density of states and transport in these structures at room temperature. The system discussed here is based on polarization-induced anisotropic charge in vicinal AlGaN/GaN heterostructures. We developed a 2-sub-band model consisting of 1-D and 2-D sub-bands to describe the behavior of these wires. We find excellent agreement between our model and experimental data, confirming the channels are indeed 1-dimensional. Our demonstration of 1-dimensional electron channel arrays in this system could enable optical, electronic and magnetic devices with added functionalities and performance.
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71.10.Ca Electron gas, Fermi gas
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/MoO3 composite layer for efficient and stable hole injection in organic semiconductors

Yongbiao Zhao, Jiangshan Chen, Wei Chen, and Dongge Ma

J. Appl. Phys. 111, 043716 (2012); http://dx.doi.org/10.1063/1.3687933 (5 pages)

Online Publication Date: 27 February 2012

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We report a composite hole injection layer (HIL) composed of an ultrathin film of MoO3on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) for efficient and stable hole injection in organic semiconductors. The optimized thickness of MoO3 layer was determined to be about 0.5 nm, which was enough to increase the work function of the underlying films substantially. The composite HIL can inject holes efficiently into a variety of hole transport layers (HTLs), even that with very deep highest occupied molecular orbital (HOMO) levels. Moreover, the utilization of PEDOT:PSS/MoO3 composite HIL greatly improved the stability of hole injection in organic devices, as compared to those based on pure PEDOT:PSS or MoO3 HILs, beneficial to practical applications.
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73.30.+y Surface double layers, Schottky barriers, and work functions

Spin transport in a quantum ring in the presence of Rashba spin–orbit interaction using the S-matrix method

Farhang Fallah and Mahdi Esmaeilzadeh

J. Appl. Phys. 111, 043717 (2012); http://dx.doi.org/10.1063/1.3688354 (6 pages)

Online Publication Date: 28 February 2012

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We study spin-dependent electron transport in a quantum ring with three leads in the presence of Rashba spin–orbit interaction using the S-matrix method. The effects of coupling between the leads and the ring on spin transport properties are taken into account. The conditions needed for perfect spin polarization, including the value of electron energy, the angles between the leads, the coupling constant of the leads and the Rashba constant are calculated, using contour maps. It is shown that total spin filtering with zero reflection is possible for low coupling constant as well as high coupling constant. In addition, we obtain the maximum value of the lead coupling constant at which perfect spin polarization can take place.
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72.25.-b Spin polarized transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
FREE

Interface states at the SiN/AlGaN interface on GaN heterojunctions for Ga and N-polar material

Ramya Yeluri, Brian L. Swenson, and Umesh K. Mishra

J. Appl. Phys. 111, 043718 (2012); http://dx.doi.org/10.1063/1.3687355 (5 pages) | Cited 1 time

Online Publication Date: 28 February 2012

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Dielectric passivation is important to improve the stability and reliability of gallium nitride based semiconductor devices. We need to characterize various dielectrics and their interfaces to nitrides accurately to be able to exploit the benefits efficiently. Earlier, B. L. Swenson and U. K. Mishra [J. Appl. Phys. 106, 064902 (2009)] have detailed a photo-assisted high frequency CV characterization technique for the Ga-polar SiN/GaN interface that gives an accurate value of interface state density (Dit) across the bandgap of the dielectric. In this work, we extend the technique to study the interface states at the SiN/AlGaN interface on GaN for Ga and N polar material. This simulates the AlGaN/GaN HEMT structure. A MIS-type structure comprised of a metal on SiN on an AlGaN/GaN heterojunction was used for the study. For a structure with 1 nm AlGaN interlayer, a peak interface state density of 2.8 × 1012 cm−2 eV−1 was measured. For Ga polar devices, the measured Dit decreases with increasing AlGaN thickness. In the N-polar case, the measured Dit increases with increasing AlGaN thickness. The variations of measured Dit with AlGaN thickness, in both cases, can be explained by screening from the accumulation charge at the AlGaN/GaN interface.
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85.30.Tv Field effect devices

Finite size suppression of the weak field magnetoresistance of lightly phosphorous-doped silicon

Nicholas A. Porter and Christopher H. Marrows

J. Appl. Phys. 111, 043719 (2012); http://dx.doi.org/10.1063/1.3688305 (6 pages)

Online Publication Date: 29 February 2012

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We report magnetoresistance measurements of lightly phosphorous doped silicon in samples that are fabricated from silicon-on-insulator wafers and so confined in one dimension. All three principal magnetic field orientations were studied at 50 and 270 K for thicknesses between 1.5−530 μm, and as thin as 150 nm at 270 K. The weak field magnetoresistance was suppressed in the orientations with the field in the sample plane when the sample is thinner than ∼1 μm at 270 K (∼10 μm at 50 K). This suppression occurred for samples that are much thicker than the carrier mean free path and the Debye screening length, and the relevant lengthscale is instead the energy relaxation length.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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