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15 Feb 2005

Volume 97, Issue 4, Articles (04xxxx)

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Unipolar space-charge limited current through layers with a disparate concentration of shallow traps: Experiment and model

Arne Fleissner, Wieland Weise, and Heinz von Seggern

J. Appl. Phys. 97, 043701 (2005); http://dx.doi.org/10.1063/1.1840094 (6 pages) | Cited 2 times

Online Publication Date: 20 January 2005

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The influence of the spatial distribution of trap states on unipolar space-charge limited current (SCLC) is investigated experimentally and theoretically. Thin-layered films of the small molecule organic semiconductor N,N′-di(1-naphtyl)-N,N′-diphenylbenzidine (α-NPD) are vapor deposited on indium tin oxide, with aluminum as the counter electrode. The small molecule 4,4′,4″-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA), which creates well-known shallow traps for holes, is used as dopant. The realized organic films consist of three layers, one of which is homogeneously doped. The influence of the spatial position of the doped layer on the current–voltage characteristics of the diodes is examined. Compared to an undoped device, the current density is strongly decreased and varies over orders of magnitude for the different spatial positions of the doped layer. It is shown that traps near the injecting electrode have the most pronounced effect on SCLC. A model for unipolar SCLC through a system of homogeneous layers with different trapping parameters for shallow traps is presented. The model quantitatively describes the experimental data and is used to calculate the spatial distributions of the charge-carrier density and the electric-field strength in the differently doped devices.
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85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling
73.50.Fq High-field and nonlinear effects
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.up Other materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.S- Impurities in crystals
71.55.-i Impurity and defect levels

Modeling of electron–electron scattering in Monte Carlo simulation of quantum cascade lasers

Olivier Bonno, Jean-Luc Thobel, and François Dessenne

J. Appl. Phys. 97, 043702 (2005); http://dx.doi.org/10.1063/1.1840100 (7 pages) | Cited 41 times

Online Publication Date: 21 January 2005

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A theoretical model of electron–electron scattering in multisubband systems is proposed and used to set up a Monte Carlo simulator of quantum cascade lasers. Special features of the electron–electron scattering model are the following: (i) A fast and accurate computation of bare potential matrix elements by means of Fourier analysis is developed. (ii) A screening model is proposed that allows us to describe intersubband matrix elements. (iii) Nonequilibrium screening factors, defined through an effective subband temperature for each subband, are periodically reevaluated. (iv) The developed algorithm makes use of rejection procedures in order to determine the correct number of scattering events as well as the distribution of the final states. Other characteristics of the model are the following: the energy levels and the wave functions are determined in a self-consistent way, the Pauli exclusion principle is included, and the periodicity of the structure is accounted for. This model is applied to the study of a terahertz resonant phonon quantum cascade laser. A large influence of the screening model on the subband population is demonstrated. For the considered design, emission at a frequency as low as 1 THz is confirmed. We have found that the magnitude of population inversion phenomena may be strongly sensitive to electron–electron scattering, reducing the possible performance near 1 THz.
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42.55.Px Semiconductor lasers; laser diodes
73.20.At Surface states, band structure, electron density of states
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Time evolution studies of the electrostatic surface potential of low-temperature-grown GaAs using electrostatic force microscopy

S. W. Howell and D. B. Janes

J. Appl. Phys. 97, 043703 (2005); http://dx.doi.org/10.1063/1.1844615 (7 pages) | Cited 2 times

Online Publication Date: 24 January 2005

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An electrostatic force microscope was used to measure the electrostatic surface potential of low-temperature-grown GaAs (LTG:GaAs) before and after the removal of the native oxide layer. The surface potential of oxidized LTG:GaAs was found to be 450±50 mV with respect to a bare Au reference. This was consistent with the known work function of Au and energy bands of LTG:GaAs. After removal of the oxide layer using a chemical etch, the surface potential of the LTG:GaAs was found to evolve as time passed. The observed transient behavior depended both on the environment and the particular chemical etchant used to remove the native surface oxide, with time constants ranging from approximately 1 to 10 h. The behavior can be explained in terms of the decay of a charge sheet or dipole at the surface. The experiments provide insights into the surface electrical properties of LTG:GaAs and, indirectly, stoichiometric at critical stages of typical device fabrication processes.
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81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.61.Ey III-V semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Cf Surface cleaning, etching, patterning
73.20.At Surface states, band structure, electron density of states
68.37.-d Microscopy of surfaces, interfaces, and thin films

Pressure behavior of beryllium-acceptor level in gallium nitride

H. Teisseyre, I. Gorczyca, N. E. Christensen, A. Svane, F. B. Naranjo, and E. Calleja

J. Appl. Phys. 97, 043704 (2005); http://dx.doi.org/10.1063/1.1845581 (6 pages) | Cited 1 time

Online Publication Date: 24 January 2005

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Beryllium is a promising dopant for obtaining an efficient p-type conductivity of GaN. A high-pressure study of the donor-acceptor-pair (DAP) photoluminescence line at 3.39 eV in Be-doped GaN samples is reported, together with ab initio calculations of the electronic structure of GaN:Be under pressure. The analysis confirms the formation of a Be-acceptor state which is involved in the DAP photoluminescence. Different properties of the Mg- and the Be-acceptor states in GaN are found. The Be level is located ∼ 100–140 meV lower in the band gap than that of Mg, and its pressure coefficient is lower by approximately 3–4 meV/GPa.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
62.50.-p High-pressure effects in solids and liquids
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Determination of band-offset enhanced in InGaAsP–InGaAsP strained multiquantum wells by photocurrent measurements

Davide Tari, Milena De Giorgi, Roberto Cingolani, Ermanno Foti, and Claudio Coriasso

J. Appl. Phys. 97, 043705 (2005); http://dx.doi.org/10.1063/1.1850602 (4 pages) | Cited 1 time

Online Publication Date: 25 January 2005

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We experimentally determine the band offset of strain-compensated InGaAsP–InGaAsP multiquantum-well (MQW) heterostructures, emitting at 1.55 μm, that were grown by metal-organic chemical vapor deposition. A band offset value of about 56% is found for the conduction band, which is higher than the value reported for the unstrained structure. The temperature dependence of the photoluminescence intensity shows that the unipolar detrapping of carriers in such MQWs is more efficient than the thermal activation of excitons.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
73.20.At Surface states, band structure, electron density of states
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Effect of electron-nuclear spin interactions for electron-spin qubits localized in InGaAs self-assembled quantum dots

Seungwon Lee, Paul von Allmen, Fabiano Oyafuso, Gerhard Klimeck, and K. Birgitta Whaley

J. Appl. Phys. 97, 043706 (2005); http://dx.doi.org/10.1063/1.1850605 (8 pages) | Cited 6 times

Online Publication Date: 25 January 2005

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The effect of electron-nuclear spin interactions on qubit operations is investigated for a qubit represented by the spin of an electron localized in an InGaAs self-assembled quantum dot. The localized electron wave function is evaluated within the atomistic tight-binding model. The electron Zeeman splitting induced by the electron-nuclear spin interaction is estimated in the presence of an inhomogeneous environment characterized by a random nuclear spin configuration, by the dot-size distribution, alloy disorder, and interface disorder. Due to these inhomogeneities, the electron Zeeman splitting varies from one qubit to another by the order of 10−6, 10−6, 10−7, and 10−9 eV, respectively. Such fluctuations cause errors in exchange operations due to the inequality of the Zeeman splitting between two qubits. However, the error can be made lower than the quantum error threshold if an exchange energy larger than 10−4 eV is used for the operation. This result shows that the electron-nuclear spin interaction does not hinder quantum-dot based quantum computer architectures from being scalable even in the presence of inhomogeneous environments.
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73.63.Kv Quantum dots
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.70.Jp Nuclear states and interactions
73.23.-b Electronic transport in mesoscopic systems
03.67.Lx Quantum computation architectures and implementations

Transport and magnetic properties of metallic La1−xPbxNiO3−δ (0.0 ⩽ x ⩽ 0.1)

Sudipta Pal, B. K. Chaudhuri, S. Neeleshwar, Y. Y. Chen, and H. D. Yang

J. Appl. Phys. 97, 043707 (2005); http://dx.doi.org/10.1063/1.1852691 (6 pages) | Cited 4 times

Online Publication Date: 25 January 2005

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Transport properties (resistivity and thermoelectric power) of Pb doped LaNiO3 viz. La1−xPbxNiO3−δ (0.0 ⩽ x ⩽ 0.1) show metallic behavior over a wide range of temperature (10–550 K). Pb doping (up to 10%) at the La site does not destroy the metallic behavior of LaNiO3. The paramagnetic susceptibility χ decreases with Pb doping. Above 50 K, χ is almost temperature independent and exhibits Pauli like features with a small additional Curie law contribution. The resistivity ρ increases with Pb doping though the thermoelectric power does not change proportionately, indicating that Pb doping does not introduce much disorder in the system. A linear T dependence of ρ observed above 150 K suggests the importance of electron–phonon (el–ph) interactions but at temperature below 150 K, ρ follows a T1.5 dependence. The estimated el–ph interaction constant λ increases (0.80–2.53) with Pb doping (x = 0.0–0.1). No saturation of resistivity has been observed even up to 550 K with x ⩽ 0.1. The phonon frequency νph ∼ 3444 cm−1 of the undoped sample calculated from the absorption peak of the Fourier transform infrared spectra agrees well with that at ∼ 3025 cm−1 estimated from the reported heat capacity data.
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75.20.Ck Nonmetals
75.30.Cr Saturation moments and magnetic susceptibilities
72.15.Jf Thermoelectric and thermomagnetic effects
72.80.Sk Insulators
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
63.20.K- Phonon interactions
78.30.Hv Other nonmetallic inorganics

Buried stressors in nitride semiconductors: Influence on electronic properties

A. E. Romanov, P. Waltereit, and J. S. Speck

J. Appl. Phys. 97, 043708 (2005); http://dx.doi.org/10.1063/1.1851016 (13 pages) | Cited 10 times

Online Publication Date: 26 January 2005

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An analysis is presented on the effect of the strain field originating from a subsurface stressor (point source of dilatation or a dilatating ellipsoidal inclusion) on the electronic properties of nitride semiconductors. With good accuracy, real quantum dots can be modeled as such stressors. We consider the following material structure design: a uniform semi-infinite GaN matrix with a buried stressor or a GaN matrix with a single (In,Ga)N quantum well, which is grown pseuodomorphically between the stressor and the free surface. We utilize isotropic elasticity to determine the strain field in the structures under investigation. We then apply a k∙p perturbation theory approach to examine the shifts of the conduction and valence band edges caused by the stressor. We find lateral confinement for electrons and holes, which can be proposed for the realization of strain-induced quantum dots in the quantum well.
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73.21.Fg Quantum wells
73.21.La Quantum dots
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
77.22.Ej Polarization and depolarization
71.15.-m Methods of electronic structure calculations

Monte Carlo investigation of current voltage and avalanche noise in GaN double-drift impact diodes

Antanas Reklaitis and Lino Reggiani

J. Appl. Phys. 97, 043709 (2005); http://dx.doi.org/10.1063/1.1853498 (8 pages) | Cited 4 times

Online Publication Date: 28 January 2005

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By Monte Carlo simulations, we investigate the current voltage characteristics and the current noise in GaN homojunction double-drift impact avalanche diodes. We have found that a suppression of avalanche noise from the standard excess noise factor starts when the dielectric relaxation time becomes comparable or less than the carrier transit time. The suppression reaches values down to three orders of magnitude when the current approaches the electrical breakdown regime. The negative feedback between fluctuations of the space charge and of the number of electron-hole pairs generated under avalanche conditions is found to be responsible for this giant suppression of noise.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Correlation between macroscopic transport parameters and microscopic electrical properties in GaN

H. Witte, A. Krtschil, E. Schrenk, K. Fluegge, A. Dadgar, and A. Krost

J. Appl. Phys. 97, 043710 (2005); http://dx.doi.org/10.1063/1.1854212 (4 pages)

Online Publication Date: 28 January 2005

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In GaN layers grown by metal-organic vapor phase epitaxy on sapphire substrates the temperature-dependent Hall (TDH) and photo-Hall-effect (PHE) measurements show essential differences between undoped and Si-doped GaN. In undoped GaN the maximum of the Hall mobility occurs at temperatures near 300 K with a low value. In PHE, an illumination introduces an enhancement of the mobility and a decrease of the electron density. In contrast, in Si-doped GaN the maximum Hall mobility is higher by a factor of 10 and is observed at temperatures between 100 and 180 K. The photoinduced changes in the mobility and electron density are only marginal. Intensity dependent PHE measurements suggest the existence of internal potential barriers caused by inhomogeneities in the undoped samples. These results are combined with the surface-potential roughness on a microscale, as determined by scanning surface-potential microscopy (SSPM). In SSPM the undoped layers show strong potential fluctuations while they are lower for the Si-doped GaN samples. A correlation among the rms roughness of the surface potential, the maximum Hall mobility in TDH, and the maximum changes of the photo-Hall mobility is observed. In undoped GaN the mobility seems to be determined by the scattering at inner potential barriers stemming from structural inhomogeneities.
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73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Pz Photoconduction and photovoltaic effects
68.55.-a Thin film structure and morphology
68.37.-d Microscopy of surfaces, interfaces, and thin films

Transport mechanism in lightly doped hydrogenated microcrystalline silicon thin films

A. Dussan and R. H. Buitrago

J. Appl. Phys. 97, 043711 (2005); http://dx.doi.org/10.1063/1.1848193 (5 pages) | Cited 9 times

Online Publication Date: 28 January 2005

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Boron-doped microcrystalline silicon films have been deposited in a plasma-enhanced chemical vapor deposition system using silane diluted in hydrogen, and diborane (B2H6) as a dopant gas. The temperature dependence of the dark conductivity has been measured from 120 to 420 K in all samples. In the high-temperature range above room temperature, the carrier transport is found to be thermally activated, with a single activation energy that changes with the B2H6 compensation degree. In the low-temperature range (300–120 K), variable range hopping (VRH) was established as a predominant electronic transport mechanism for all samples, with the exception of the sample with a diborane concentration of 12.5 ppm. A model for Mott’s VRH, referred to as the “diffusional model,” which yields a relation between the conductivity and the localized density of gap states, is presented. Using classical equations from the percolation theory and the diffusional model, the density of states near the Fermi level, as well as the hopping parameters, are calculated. A correlation between the hopping parameters for both models is deduced. A numerical factor that improves the value of each parameter is calculated.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Cw Elemental semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.20.At Surface states, band structure, electron density of states
66.30.Dn Theory of diffusion and ionic conduction in solids
66.30.H- Self-diffusion and ionic conduction in nonmetals

The influence of nonmagnetic seed layers on the magnetotransport properties of magnetic tunnel transistors with a silicon collector

Sebastiaan van Dijken, Xin Jiang, and Stuart S. P. Parkin

J. Appl. Phys. 97, 043712 (2005); http://dx.doi.org/10.1063/1.1814422 (8 pages) | Cited 2 times

Online Publication Date: 28 January 2005

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The magnetotransport properties of magnetic tunnel transistors (MTTs) with a CoFe/Cu/NiFe spin-valve base and a Si(001) collector are studied as a function of seed layer material and thickness. The insertion of a nonmagnetic Cu or Au seed layer between the metal spin valve and the silicon is found to significantly enhance the output current and magnetic-field sensitivity of the MTT device. In contrast, the use of a Pt or Pd seed layer only slightly improves the properties of the MTT, while seed layers of Ta and Ti are found to deteriorate the output current and tunnel barrier breakdown voltage of the MTTs. Secondary-ion-mass spectroscopy is used to provide complementary information about the base∕collector interface properties of the MTTs with and without seed layers.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
75.47.Np Metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.25.Ba Spin polarized transport in metals

Effects of buffer layers on the structural and electronic properties of InSb films

X. Weng, N. G. Rudawski, P. T. Wang, R. S. Goldman, D. L. Partin, and J. Heremans

J. Appl. Phys. 97, 043713 (2005); http://dx.doi.org/10.1063/1.1841466 (7 pages) | Cited 13 times

Online Publication Date: 28 January 2005

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We have investigated the effects of various buffer layers on the structural and electronic properties of n-doped InSb films. We find a significant decrease in room-temperature electron mobility of InSb films grown on low-misfit GaSb buffers, and a significant increase in room-temperature electron mobility of InSb films grown on high-misfit InAlSb or step-graded GaSb+InAlSb buffers, in comparison with those grown directly on GaAs. Plan-view transmission electron microscopy (TEM) indicates a significant increase in threading dislocation density for InSb films grown on the low-misfit buffers, and a significant decrease in threading dislocation density for InSb films grown on high-misfit or step-graded buffers, in comparison with those grown directly on GaAs. Cross-sectional TEM reveals the role of the film/buffer interfaces in the nucleation (filtering) of threading dislocations for the low-misfit (high-misfit and step-graded) buffers. A quantitative analysis of electron mobility and carrier-concentration dependence on threading dislocation density suggests that electron scattering from the lattice dilation associated with threading dislocations has a stronger effect on electron mobility than electron scattering from the depletion potential surrounding the dislocations. Furthermore, while lattice dilation is the predominant mobility-limiting factor in these n-doped InSb films, ionized impurity scattering associated with dopants also plays a role in limiting the electron mobility.
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81.05.Bx Metals, semimetals, and alloys
82.45.Mp Thin layers, films, monolayers, membranes
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