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15 Aug 2010

Volume 108, Issue 4, Articles (04xxxx)

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J. Appl. Phys. 108, 041901 (2010); http://dx.doi.org/10.1063/1.3474648 (2 pages)

Sergei V. Kalinin, Nava Setter, and Andrei L. Kholkin
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back to top Electronic Structure and Transport

Microscopic theory of electron cotunneling through quantum dots

Fuping Cheng and Weidong Sheng

J. Appl. Phys. 108, 043701 (2010); http://dx.doi.org/10.1063/1.3475148 (4 pages) | Cited 3 times

Online Publication Date: 16 August 2010

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A microscopic theory is presented for electron cotunneling through quantum dots in the Coulomb blockade regime. Beyond the semiclassic framework of phenomenological models, a fully quantum mechanical solution for cotunneling of electrons through a one-dimensional quantum dot is obtained by using a quantum transmitting boundary method without any fitting parameters. Elastic and inelastic cotunneling conductance is calculated as a function of the energy of the incident electron. It is revealed that the cotunneling current contains a significant term proportional to V2 (V being the bias voltage) in additional to the well-known V3 term. The result also indicates that the cotunneling conductance exhibits little dependence on the spin configuration of the incident and confined electrons.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Gk Tunneling

Short range scattering mechanism of type-II GaSb/GaAs quantum dots on the transport properties of two-dimensional electron gas

Guodong Li, Hong Yin, Qinsheng Zhu, Hiroyuki Sakaki, and Chao Jiang

J. Appl. Phys. 108, 043702 (2010); http://dx.doi.org/10.1063/1.3467520 (5 pages) | Cited 3 times

Online Publication Date: 16 August 2010

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We have studied the scattering process of AlGaAs/GaAs two-dimensional electron gas with the nearby embedded GaSb/GaAs type-II quantum dots (QDs) at low temperature. Quantum Hall effect and Shubnikov–de Haas oscillation were performed to measure the electron density n2D, the transport lifetime τt, and the quantum lifetime τq under various biased gate voltage. By comparing measured results of QDs sample with that of reference sample without embedded QDs, mobilities (transport mobility μt and quantum mobility μq) dominated by GaSb QDs scattering were extracted as functions of n2D. It was found that the ratios of τt to τq were varying within the range of 1–4, implying the scattering mechanism belonging to the sort of short-range interaction. In the framework of Born approximation, a scattering model considering rectangular-shaped potential with constant barrier height was successfully applied to explain the transport experimental data. In addition, an oscillating ratio of τt/τq with the increasing n2D was predicted in the model.
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73.63.Kv Quantum dots
72.20.My Galvanomagnetic and other magnetotransport effects
73.21.La Quantum dots
73.43.-f Quantum Hall effects

Depth analysis of boron diffusion in MgO/CoFeB bilayer by x-ray photoelectron spectroscopy

Y. Lu, B. Lépine, G. Jézéquel, S. Ababou, M. Alnot, J. Lambert, A. Renard, M. Mullet, C. Deranlot, H. Jaffrès, F. Petroff, and J.-M. George

J. Appl. Phys. 108, 043703 (2010); http://dx.doi.org/10.1063/1.3465308 (6 pages) | Cited 4 times

Online Publication Date: 17 August 2010

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We have studied the boron (B) diffusion in MgO/CoFeB bilayer by x-ray photoelectron spectroscopy depth analysis. A large concentration of B (B/Mg = 0.16) was found to diffuse into the MgO barrier after 350 °C annealing. The boron in MgO is in a highly oxidized B3+ state and is homogenously distributed in the whole barrier. The important B diffusion in MgO could be related to the CoFeB crystallization process which begins from the under CoFeB/Ru interface and pushes boron atoms to diffuse into the MgO barrier during annealing.
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68.35.Fx Diffusion; interface formation
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Gh Other heat and thermomechanical treatments
81.65.Mq Oxidation
64.70.K- Solid-solid transitions
64.70.kd Metals and alloys

Electronic properties of the high electron mobility Al0.56In0.44Sb/Ga0.5In0.5Sb heterostructure

L. Desplanque, D. Vignaud, S. Godey, E. Cadio, S. Plissard, X. Wallart, P. Liu, and H. Sellier

J. Appl. Phys. 108, 043704 (2010); http://dx.doi.org/10.1063/1.3475709 (6 pages) | Cited 3 times

Online Publication Date: 17 August 2010

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Electronic properties of the Al0.56In0.44Sb/Ga0.5In0.5Sb heterostructure grown by molecular beam epitaxy are investigated. We measure by means of x-ray photoemission spectroscopy, photoluminescence, and Hall effect measurements the key parameters involved in the achievement of a high speed and very low power consumption field effect transistor: conduction and valence band offsets, energy gaps of channel and barrier materials, electron effective mass, and density of states in the channel. We observe the influence of the quantum well thickness on the electron Hall mobility and sheet carrier density. A type I heterostructure exhibiting a room temperature electron mobility of 25 000 cm2 V−1 s−1 with a sheet carrier density of 1.5×1012 cm−2 is demonstrated for the widest channel. We show that the thickness of the channel influences both Hall density and mobility through a multisubband occupancy. We discuss about the scattering mechanisms limiting the mobility in the second subband.
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73.21.Fg Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Tv Field effect devices
73.43.Fj Novel experimental methods; measurements
78.55.Cr III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Emergence of current branches in a series array of negative differential resistance circuit elements

Huidong Xu and Stephen W. Teitsworth

J. Appl. Phys. 108, 043705 (2010); http://dx.doi.org/10.1063/1.3475988 (4 pages) | Cited 1 time

Online Publication Date: 18 August 2010

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We study a series array of nonlinear electrical circuit elements that possess negative differential resistance and find that heterogeneity in the element properties leads to the presence of multiple branches in current–voltage curves and a nonuniform distribution of voltages across the elements. An inhomogeneity parameter rmax is introduced to characterize the extent to which the individual element voltages deviate from one another, and it is found to be strongly dependent on the rate of change of applied voltage. Analytical expressions are derived for the dependence of rmax on voltage ramping rate in the limit of fast ramping and are confirmed by direct numerical simulation.
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84.30.Bv Circuit theory
02.60.-x Numerical approximation and analysis

Many-particle transport in the channel of quantum wire double-gate field-effect transistors with charged atomistic impurities

G. Albareda, X. Saura, X. Oriols, and J. Suñé

J. Appl. Phys. 108, 043706 (2010); http://dx.doi.org/10.1063/1.3455878 (11 pages)

Online Publication Date: 19 August 2010

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One of the most reported causes of variations in electron devices characteristics (coming from the atomistic nature of matter) are discrete doping induced fluctuations. In this work we highlight the importance of accurately accounting for (time-dependent) coulomb correlations among (transport) electrons in the analysis of such fluctuations. In particular, we study the effect of single ionized dopants on the performance of a quantum wire double-gate metal-oxide-semiconductor field-effect transistor, mainly when its lateral dimensions approach the effective cross section of the charged impurities. In this regard, we use a recently developed many-particle semiclassical simulation approach by Albareda et al. [Phys. Rev. B 79, 075315 (2009)] which provides an accurate treatment of electron–electron and electron–impurity interactions (avoiding the mean-field approximation). We reveal the significant impact of the sign and position of the impurity along the transistor channel on the on-current, the threshold voltage, the distribution of the current in the channel cross-section, the transmission probabilities, and the distribution of transit times. We find that neglecting the (time-dependent) coulomb correlations among (transport) electrons can lead to misleading predictions of the previous results.
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85.30.Tv Field effect devices

Subgap modulated photocurrent spectroscopy and its application to the study of the solar cell absorber defect distributions

Z. Djebbour, J. Serhan, A. Migan-Dubois, and D. Mencaraglia

J. Appl. Phys. 108, 043707 (2010); http://dx.doi.org/10.1063/1.3456004 (12 pages) | Cited 2 times

Online Publication Date: 19 August 2010

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In this paper, a theoretical background of subgap modulated photocurrent experiment is presented. It allows the investigation of the density of states (DOS) distribution, directly from the active region of a semiconductor heterojunction device. The junction is illuminated with a modulated subgap light excitation (i.e., light with photon energy lower than the band gap of the active layer). Under specific considerations for the applied reverse bias voltage and the bias-light level, a simple theoretical relation of the imaginary part of the photocurrent versus the modulation angular frequency allows the determination of the energy profile of the gap states. This technique has been successfully applied to a Ga free Cu(In,Ga)Se2 based solar cell to investigate the DOS distribution in the band gap of the absorber. Two distinct defect distributions have been exhibited in the absorber layer of the studied solar cell.
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72.40.+w Photoconduction and photovoltaic effects
79.60.-i Photoemission and photoelectron spectra
71.55.-i Impurity and defect levels

Ballistic transport through electric field modulated graphene periodic magnetic barriers

R. Biswas, A. Biswas, N. Hui, and C. Sinha

J. Appl. Phys. 108, 043708 (2010); http://dx.doi.org/10.1063/1.3467778 (7 pages) | Cited 7 times

Online Publication Date: 23 August 2010

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The transmission coefficient and the ballistic conductance are studied theoretically for a Dirac fermion through the graphene periodic magnetic barriers modulated by a homogeneous in-plane electric field. The transmission is highly asymmetric for zero and low biased conditions of the system. In contrast, it turns out to be symmetric in case of strongly modulated (by electric field) magnetic barriers and becomes independent of the number of barriers due to the predominant Klein tunneling effect. Interesting electric field effects are noted on the angular transmission properties of the chiral carriers. The conductivity profile exhibits some negative differential conducting regions, the number and the sharpness of the regions being intimately related to the number of barriers and the Fermi energy of the system.
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73.23.Ad Ballistic transport
72.80.Vp Electronic transport in graphene
05.30.Fk Fermion systems and electron gas
75.70.Ak Magnetic properties of monolayers and thin films

Temperature dependent transport properties of p-Pb1−xMnxSe films

Y. H. Sun, T. Lin, K. H. Gao, Z. G. Hu, H. Z. Wu, P. X. Yang, N. Dai, and J. H. Chu

J. Appl. Phys. 108, 043709 (2010); http://dx.doi.org/10.1063/1.3478708 (4 pages) | Cited 2 times

Online Publication Date: 23 August 2010

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Hall measurements are performed to survey electrical properties of p-Pb1−xMnxSe (x ≈ 0.04) films grown by molecular beam epitaxy technique. It is indicated that these films are approaching the metal-insulator transition from the metallic side. Weak localization effect was observed up to about 50 K. The deduced phase-breaking time τϕ on temperature is interpreted according to the concept of the electron–electron scattering in highly disordered bulk conductors.
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81.05.Hd Other semiconductors
73.61.Le Other inorganic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.30.+h Metal-insulator transitions and other electronic transitions

Effects of symmetry-breaking perturbations on excitonic states bound to systems of reduced symmetry

S. Francoeur and S. Marcet

J. Appl. Phys. 108, 043710 (2010); http://dx.doi.org/10.1063/1.3457851 (12 pages) | Cited 1 time

Online Publication Date: 24 August 2010

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Using an invariant expansion, we build an Hamiltonian describing the influence of the crystal-field, the electron-hole exchange interaction, and any symmetry-breaking perturbations on the fine structure of excitons bound to systems of reduced symmetry: D2d, C3v, and C2v. Several perturbations are considered, including, but not limited to, an electric field, a magnetic field, a strain field, and their combinations. For each symmetry system considered, symmetrized excitonic wave functions, build from heavy- and light-holes states, are used to expand the Hamiltonian in the form of matrices, whose eigenvalues directly provide the energy of the excitonic states and whose eigenstates can be used to determine oscillator strengths of optical transitions. Using this model, we satisfactorily reproduce the excitonic emission observed from nitrogen dyads in GaAs and tellurium dyads in strained ZnSe. We also present Hamiltonians for independent heavy- and light-hole subsystems. Comparing the two models, we demonstrate that the splitting observed in strained quantum dots of C2v symmetry does not necessarily imply a significant anisotropic exchange interaction. This splitting can be produced by a weak coupling between heavy- and light-hole bands.
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73.21.La Quantum dots
71.70.Gm Exchange interactions
71.35.-y Excitons and related phenomena
71.70.Ch Crystal and ligand fields
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Accurate carrier-type determination of nonhomogenously doped diamond

N. Yom-Tov, C. Saguy, A. Bolker, R. Kalish, and Y. E. Yaish

J. Appl. Phys. 108, 043711 (2010); http://dx.doi.org/10.1063/1.3463395 (5 pages) | Cited 3 times

Online Publication Date: 26 August 2010

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Electrical properties of B-doped homoepitaxialy grown diamond are characterized with and without mesa structures by Hall effect measurements as function of temperature in the as-grown state and following oxygen reactive ion etching (RIE). The extracted carrier type, concentration, and mobility are found to depend on the measurement contact configuration. For measurements performed without mesa major differences, even in carrier type, are found following the RIE treatment, however no changes what so ever are observed when measuring with a mesa structure. Finite element simulation confirms that carrier concentration or/and mobility inhomogeneities in the regions surrounding the contacts in Hall effect measurements using the Van der Pauw configuration can result in wrong assignments of carrier type, concentration and mobility.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Fr Low-field transport and mobility; piezoresistance
81.05.Cy Elemental semiconductors
81.05.ug Diamond

Revealing substructures of H4 and H5 hole traps in p-type InP using Laplace deep-level transient spectroscopy

R. Darwich and A. A. Mani

J. Appl. Phys. 108, 043712 (2010); http://dx.doi.org/10.1063/1.3478744 (5 pages)

Online Publication Date: 26 August 2010

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New substructures of H4 and H5 hole traps have been revealed using Laplace deep-level transient spectroscopy. Our measurements show that the hole traps H4 and H5 can have at least three components for each. Moreover, the activation energies are deduced and the microscopic nature of these substructures is discussed.
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71.55.Eq III-V semiconductors
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors

Origins of magnetism in transition metal doped CuI

Jing Wang, Jingbo Li, and Shu-Shen Li

J. Appl. Phys. 108, 043713 (2010); http://dx.doi.org/10.1063/1.3471802 (5 pages) | Cited 3 times

Online Publication Date: 27 August 2010

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Cupric iodide is a p-type semiconductor and has a large band gap. Doping of Mn, Co, and Ni are found to make γ-CuI ferromagnetic ground state, while Cr-doped and Fe-doped CuI systems are stabilized in antiferromagnetic configurations. The origins of the magnetic ordering are demonstrated successfully by the phenomenological band coupling model based on d-d level repulsions between the dopant ions. Furthermore, using a molecular-orbital bonding model, the electronic structures of the doped CuI are well understood. According to Heisenberg model, high-TC may be expected for CuI:Mn and CuI:Ni if there are no native defects or other impurities.
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71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
61.72.up Other materials
75.10.Jm Quantized spin models, including quantum spin frustration
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