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15 Apr 2002

Volume 91, Issue 8, pp. 4791-5508

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Minority-carrier kinetics in heavily doped GaAs:C studied by transient photoluminescence

A. Maaßdorf, S. Gramlich, E. Richter, F. Brunner, M. Weyers, G. Tränkle, J. W. Tomm, Y. I. Mazur, D. Nickel, V. Malyarchuk, T. Günther, Ch. Lienau, A. Bärwolff, and T. Elsaesser

J. Appl. Phys. 91, 5072 (2002); http://dx.doi.org/10.1063/1.1456244 (7 pages) | Cited 4 times

Online Publication Date: 29 March 2002

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Room-temperature photoluminescence decay time measurements in heavily doped GaAs:C-layers designed as base layers for heterojunction bipolar transistors are reported. These measurements provide access to nonequilibrium minority carrier lifetimes that determine the current gains of those devices. By systematically studying transient luminescence spectra over a wide range of excitation densities between 1013 and 1018 cm−3, we demonstrate the importance of carrier trapping processes at low excitation densities. Optimized excitation conditions that achieve trap saturation but also avoid stimulated emission are found for densities of (1–3)×1017 cm−3/pulse. Detection is limited to a spectral window well above the energy gap (beyond 1.5 eV). Values for both Auger and radiative recombination coefficients are given. © 2002 American Institute of Physics.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors
73.61.Ey III-V semiconductors
85.30.Pq Bipolar transistors
78.66.Fd III-V semiconductors

Thermal conduction in doped single-crystal silicon films

M. Asheghi, K. Kurabayashi, R. Kasnavi, and K. E. Goodson

J. Appl. Phys. 91, 5079 (2002); http://dx.doi.org/10.1063/1.1458057 (10 pages) | Cited 71 times

Online Publication Date: 29 March 2002

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This work measures the thermal conductivities along free-standing silicon layers doped with boron and phosphorus at concentrations ranging from 1×1017 to 3×1019 cm−3 at temperatures between 15 and 300 K. The impurity concentrations are measured using secondary ion mass spectroscopy (SIMS) and the thermal conductivity data are interpreted using phonon transport theory accounting for scattering on impurities, free electrons, and the layer boundaries. Phonon-boundary scattering in the 3-μm-thick layers reduces the thermal conductivity of the layers at low temperatures regardless of the level of impurity concentration. The present data suggest that unintentional impurities may have strongly reduced the conductivities reported previously for bulk samples, for which impurity concentrations were determined from the electrical resistivity rather than from SIMS data. This work illustrates the combined effects of phonon interactions with impurities, free electrons, and material interfaces, which can be particularly important in semiconductor devices. © 2002 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.20.K- Phonon interactions
61.72.S- Impurities in crystals
71.38.-k Polarons and electron-phonon interactions
63.20.kp Phonon-defect interactions

Electronic property variations due to an embedded potential barrier layer in modulation-doped step quantum wells

T. W. Kim, D. U. Lee, D. C. Choo, M. Jung, K. H. Yoo, G. Comanescu, and B. D. McCombe

J. Appl. Phys. 91, 5089 (2002); http://dx.doi.org/10.1063/1.1454198 (4 pages) | Cited 3 times

Online Publication Date: 29 March 2002

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Electronic property variations of a two-dimensional electron gas (2DEG) in modulation-doped step quantum wells due to an embedded potential barrier were studied by performing Shubnikov–de Haas (SdH), Van der Pauw–Hall-effect, and cyclotron resonance measurements on two kinds of InxGa1−xAs/InyAl1−yAs step quantum wells which were one without and the other with an embedded barrier. The fast Fourier transformation results for the SdH data at 1.5 K indicated the electron occupation of two subbands in both step quantum wells. The total electron carrier density and the mobility of the 2DEG in the step quantum well with an embedded barrier were smaller than those in the quantum well without an embedded barrier. The electron effective masses were determined from the slopes of the main peak absorption energies as functions of the magnetic field, and satisfied qualitatively the nonparabolicity effects in both quantum wells. The electronic subband energies, the wave functions, and the Fermi energies were calculated by using a self-consistent method taking into account exchange-correlation effects together with strain and nonparabolicity effects. These present results indicate that the electronic parameters in modulation-doped InxGa1−xAs/InyAl1−yAs step quantum wells are significantly affected by an embedded barrier. © 2002 American Institute of Physics.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
73.61.Ey III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
68.65.Fg Quantum wells
73.43.Qt Magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Spectral dependence and Hall effect of persistent photoconductivity in polycrystalline Cu(In,Ga)Se2 thin films

Th. Meyer, F. Engelhardt, J. Parisi, and U. Rau

J. Appl. Phys. 91, 5093 (2002); http://dx.doi.org/10.1063/1.1459597 (7 pages) | Cited 14 times

Online Publication Date: 29 March 2002

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We investigate persistent photoconductivity in polycrystalline Cu(In,Ga)Se2 thin films by measuring the transient behavior of their electrical conductivity under and after illumination. Characteristic nonexponential transients of the conductivity under and after illumination extend over more than four orders of magnitude in time. From this result, we conclude that the persistent photoconductivity in Cu(In,Ga)Se2 cannot be explained by the mesoscopic barrier model. Rather, it is a microscopic effect which can be understood in the frame of a large lattice relaxation model. Investigation of the conductivity under monochromatic subband gap illumination determines the minimum photon energy for the direct excitation of the persistent photoconductivity to be approximately 0.6 eV. Hall effect measurements identify the persistent photoconductivity as a hole density effect in the bulk of the Cu(In,Ga)Se2 grains, consistent with the lattice relaxation model. © 2002 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Pz Photoconduction and photovoltaic effects
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.40.+w Photoconduction and photovoltaic effects
72.80.Ga Transition-metal compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Le Other inorganic semiconductors

Modelling of magnetotransport of hot electrons in a spin-valve transistor

Jisang Hong

J. Appl. Phys. 91, 5100 (2002); http://dx.doi.org/10.1063/1.1461061 (5 pages)

Online Publication Date: 29 March 2002

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This article explores the magnitude of spin dependent collector current in a spin-valve transistor varying the combination of ferromagnetic layers at finite temperatures. In these calculations, the spatial inhomogeneity of the Schottky barrier at the emitter side and spin dependent self-energy effect in ferromagnets have been taken into account. In addition, the magnetocurrent has been presented as well. It has been ascertained that the magnitude of spin dependent collector current strongly depends on the type of spin-valve base since the inelastic scattering strength is different in each material. These calculations may help find the best structural combination of ferromagnetic layers in the spin-valve base. © 2002 American Institute of Physics.
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85.75.Hh Spin polarized field effect transistors
75.47.De Giant magnetoresistance
72.25.Ba Spin polarized transport in metals
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.30.+y Surface double layers, Schottky barriers, and work functions
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys

Application of analytical k.p model with envelope function approximation to intersubband transitions in n-type III–V semiconductor Γ quantum wells

C. W. Cheah, L. S. Tan, and G. Karunasiri

J. Appl. Phys. 91, 5105 (2002); http://dx.doi.org/10.1063/1.1448890 (11 pages) | Cited 8 times

Online Publication Date: 29 March 2002

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A 14-band k.p model combined with an envelope function approximation has been developed for the analysis of III–V semiconductor quantum wells by including the six Γ7, Γ8 conduction bands nonperturbatively. With appropriate approximations, the envelope functions associated with the Γ7, Γ8 bands can be expressed in terms of the two Γ6 conduction band envelope functions, which are the most important components in the electron wave function of an n-type direct-gap III–V compound semiconductor quantum well of zincblende structure. The Schrödinger-type equations for the Γ6 conduction band envelope functions are derived, together with the energy-dependent effective mass that includes the effect of band nonparabolicity, as well as the eigenenergy-dependent effective potential for the envelope wave functions. The Schrödinger-type equations and the boundary conditions for the conservation of probability flux in the 14-band k.p model are found to be different from those of the conventional effective mass model. The 14-band model is then applied to the study of intersubband transitions due to transverse magnetic (TM) and transverse electric (TE) mode infrared radiation in n-type Γ quantum wells, and the calculated absorption spectra are compared with those computed using an equivalent 8-band k.p model. It is found that the TM absorption spectra calculated using the two models are very similar, but the TE absorption spectra calculated using the 14-band model is up to 6 times higher than that calculated using the 8-band model. A design of the quantum well structure for enhancing TE absorption is also discussed. © 2002 American Institute of Physics.
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73.21.Fg Quantum wells
78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors

Direct and trap-assisted elastic tunneling through ultrathin gate oxides

F. Jiménez-Molinos, F. Gámiz, A. Palma, P. Cartujo, and J. A. López-Villanueva

J. Appl. Phys. 91, 5116 (2002); http://dx.doi.org/10.1063/1.1461062 (9 pages) | Cited 18 times

Online Publication Date: 29 March 2002

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The direct and assisted-by-trap elastic tunnel current in metal–oxide–semiconductor capacitors with ultrathin gate oxide (1.5–3.6 nm) has been studied. Bardeen’s method has been adapted to obtain the assisted tunnel current, in addition to the direct tunnel current. The dependence of the assisted current on the trap distribution in energy has also been analyzed. This allows us to obtain the trap distribution in energy from experimental current curves. Finally, we have analyzed the role of the image force, the inclusion of which can avoid a barrier height dependence on the oxide thickness. © 2002 American Institute of Physics.
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73.40.Gk Tunneling
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
84.32.Tt Capacitors

Particle size and magnetic field dependent resistivity and thermoelectric power of La0.5Pb0.5MnO3 above and below metal–insulator transition

Aritra Banerjee, Sudipta Pal, S. Bhattacharya, B. K. Chaudhuri, and H. D. Yang

J. Appl. Phys. 91, 5125 (2002); http://dx.doi.org/10.1063/1.1459618 (10 pages) | Cited 21 times

Online Publication Date: 29 March 2002

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The effect of particle size on the transport properties (resistivity and thermopower) of La0.5Pb0.5MnO3 has been investigated both in the presence and in the absence of magnetic field B=0.0–1.5 T (maximum). Grain size, dc conductivity; and the metal–insulator transition temperature Tp of the sample increase with increasing annealing time. Grain size has, however, comparatively little effect on the Seebeck coefficient S. Magnetoresistance is higher for the samples with smaller grain sizes. dc magnetic susceptibility also increases with increasing grain size. High temperature (T>θD/2) resistivity data well fit the small polaron hopping model. Polaron hopping energy WH decreases but polaron radius rp increases with the increase of grain size. In the metallic regime (for T<Tp), resistivity data fit well with ρ=ρ0+ρ2.5 T2.5 and the transport mechanism is attributed mainly to the magnon-carrier scattering (∼T2.5). In all the samples with different grain sizes, S changes sign below Tp. In contrast to magnetoresistance, application of magnetic field increases S at low temperature (T<Tp) for these samples. Thermopower data in the metallic phase (both for B=0.0 and 1.5 T) can be analyzed by considering a spin-wave fluctuation term (∼T4) in addition to the magnon-scattering term similar to the case of resistivity data. Although the variable range hopping mechanism is supported from the resistivity data (for Tp>T>θD/2), it is hard to justify this model from the temperature dependent thermopower data. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
71.30.+h Metal-insulator transitions and other electronic transitions
72.20.Fr Low-field transport and mobility; piezoresistance
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Electronic structure of ytterbium-doped strontium fluoroapatite: Photoemission and photoabsorption investigation

A. J. Nelson, T. van Buuren, C. Bostedt, K. I. Schaffers, L. J. Terminello, Mark Engelhard, and Don Baer

J. Appl. Phys. 91, 5135 (2002); http://dx.doi.org/10.1063/1.1459601 (6 pages) | Cited 4 times

Online Publication Date: 29 March 2002

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X-ray photoemission and x-ray photoabsorption were used to study the composition and the electronic structure of ytterbium-doped strontium fluoroapatite (Yb:S-FAP). High resolution photoemission measurements on the valence band electronic structure and Sr 3d, P 2p and 2s, Yb 4d and 4p, F 1s, and O 1s core lines were used to evaluate the surface and near surface chemistry of this fluoroapatite. Element specific density of unoccupied electronic states in Yb:S-FAP were probed by x-ray absorption spectroscopy at the Yb 4d (N4,5 edge), Sr 3d (M4,5 edge), P 2p (L2,3 edge), F 1s, and O 1s (K edges) absorption edges. These results provide measurements of the electronic structure and surface chemistry of this material. © 2002 American Institute of Physics.
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71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Mechanically reversible conductor–insulator transition in Mg2NiH4

Helen Blomqvist and Dag Noréus

J. Appl. Phys. 91, 5141 (2002); http://dx.doi.org/10.1063/1.1461069 (8 pages) | Cited 8 times

Online Publication Date: 29 March 2002

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An irreversible conductor-insulator transition has been observed when heating Mg2NiH4 in the temperature interval 110 to 570 K. The disappearance of the electric conductivity is concomitant with the appearance of stacking faults (or microtwinning) in the Mg2NiH4 structure, as observed by powder x-ray diffraction. However, the stacking faults are sensitive to applied mechanical pressure or grinding, and by compressing the hydride sample in a tablet press, Mg2NiH4 regains its electric conductivity as the observable amount of stacking faults is reduced. These phenomena are attributed to peculiarities connected with the stabilization of the electron-rich tetrahedral d10 [Ni(0)H4] complex by the lattice. Formally low-valent oxidation states usually demand good electron-accepting ligands with suitable π∗ or d orbitals to relieve the high electron density at the central atom. This is not possible when hydrogen is the only ligand, but the easily polarizable H− ion helps to distribute electron density by outward bonding to the lattice. This also stabilizes the [NiH4] complex. The present work shows that this stabilization mechanism is sensitive to disturbances in the lattice and that small disturbances can have profound effects on the electric conductivity of Mg2NiH4. © 2002 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.66.Fn Inorganic compounds
61.72.Nn Stacking faults and other planar or extended defects
61.72.Mm Grain and twin boundaries
84.60.Ve Energy storage systems, including capacitor banks

Plasma induced microstructural, compositional, and resistivity changes in ultrathin chemical vapor deposited titanium nitride films

R. Kröger, M. Eizenberg, C. Marcadal, and L. Chen

J. Appl. Phys. 91, 5149 (2002); http://dx.doi.org/10.1063/1.1459750 (6 pages) | Cited 17 times

Online Publication Date: 29 March 2002

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Extremely thin titanium nitride (TiN) barrier layers for Cu based interconnects were deposited using metal organic chemical vapor deposition. The effect of the subsequently performed nitrogen/hydrogen plasma treatment on the microstructure, composition, and electrical properties of these films is studied using conventional and high resolution transmission electron microscopy, Auger electron spectroscopy, and four point probe resistivity measurements. In the studied system the crystallization of the TiN film starts from an amorphous matrix and a polycrystalline morphology is developed upon the H2/N2 plasma treatment. After a short plasma treatment, most of the film is already crystalline and consists of grains of a few nanometers in diameter. Continued plasma treatment leads to grain growth and a significant reduction of contaminants such as oxygen and carbon. The resistivity of the films drops with plasma treatment time, and a correlation between resistivity and oxygen content is found, which suggests that oxygen in the grain boundaries plays a decisive role for the resistivity of the films. It is shown that the oxygen in the grain boundaries leads to an electron reflectance of 0.9. Thus, the oxygen accumulation in the grain boundaries is the limiting factor for the reduction of film resistivity by plasma treatment. © 2002 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology
52.77.-j Plasma applications
85.40.Ls Metallization, contacts, interconnects; device isolation
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.37.Lp Transmission electron microscopy (TEM)
61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.Mm Grain and twin boundaries
68.35.Fx Diffusion; interface formation

Effects of the number of periods on strain in superlattices

K. Nishida, S. Hagiwara, M. Teranishi, O. Sirakawa, A. Hirakai, and T. Katoda

J. Appl. Phys. 91, 5155 (2002); http://dx.doi.org/10.1063/1.1462419 (3 pages)

Online Publication Date: 29 March 2002

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The effect of periods on the accumulation and release of stress in GaAs/AlInAs superlattices structure is reported here. It is observed that in GaAs/AlInAs superlattices, when the Indium (In) content is greater than 10%, stress accumulates monotonically as the number of period increases. In GaAs/AlInAs superlattices with an In content of 5%, the accumulated stress is larger when the number of periods is less than 10. However when the number of periods exceeds 10, it was observed that suddenly there is a significant increase in defects and stress release. However, with any further increase in period number, there is once again an accumulation of stress. © 2002 American Institute of Physics.
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68.65.Cd Superlattices
78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors

Deep levels in strongly Si-compensated GaAs and AlGaAs

Tadashige Sato and Toshio Ishiwatari

J. Appl. Phys. 91, 5158 (2002); http://dx.doi.org/10.1063/1.1462847 (5 pages) | Cited 3 times

Online Publication Date: 29 March 2002

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Five electron traps were detected successfully in heavily Si-doped GaAs and AlxGa1−xAs of low Al content with a Si concentration of above 1×1019 cm−3 using deep level transient spectroscopy. The junctions were grown by liquid phase epitaxy and were strongly compensated. The traps were investigated for functions of the Si concentration and the AlAs mole fraction. The traps are discussed in terms using their spectra and concentration as opposed to the previous results which used point defects in the GaAs and AlGaAs. The traps show distinctive features, which can be attributed to strongly Si-compensated crystals. Three traps among them were confirmed to be DX centers. © 2002 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.uf Ge and Si
61.72.S- Impurities in crystals

Charge polarization effects and hole spectra characteristics in AlxGa1−xN/GaN superlattices

Fatna Assaoui and Pedro Pereyra

J. Appl. Phys. 91, 5163 (2002); http://dx.doi.org/10.1063/1.1464234 (7 pages) | Cited 2 times

Online Publication Date: 29 March 2002

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We study the effects of charge polarization on the extended physical properties of superlattices, such as transmission coefficients and valence band structure. We consider both linear and parabolic modulation of the band edge. Based on the theory of finite periodic systems, analytic expressions and high precision calculations of the relevant physical quantities for n-cell systems are obtained. Well-known features of these systems are identified. Besides the well-known energy band structure, we have also the field band structure, with interesting characteristics. Wider field gaps at stronger internal electric fields and higher density of field bands for larger layer widths are some of these characteristics. Well defined level density asymmetries identify the minibands induced by charge polarization or the so-called quantum confining Stark effect. We present the n-cell transmission amplitudes, transmission coefficients and miniband structures for different values of the relevant parameters. © 2002 American Institute of Physics.
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73.21.Cd Superlattices
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Transient response of a bilayer organic light emitting diode: Building-up of external and recombination currents

L. Hassine, H. Bouchriha, J. Roussel, and J.-L. Fave

J. Appl. Phys. 91, 5170 (2002); http://dx.doi.org/10.1063/1.1464212 (6 pages) | Cited 11 times

Online Publication Date: 29 March 2002

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Using a theoretical model of a bilayer organic light emitting diode, we calculate numerically the evolution of carrier densities and electric fields inside the device. The obtained results allow us to detail injection and accumulation of carriers during transient excitation. Charge densities as a function of applied voltage present two distinct thresholds which determine three operating ranges: no injection, unipolar injection, and bipolar injection. Dynamically these thresholds depend on the rise time of the applied voltage and have a clear signature in the current densities. We show that the electroluminescence threshold has static and dynamic values which may be different. Calculated external current in response to a voltage ramp presents two steps related to the evolution of the capacity of the device. This capacitive behavior is observed experimentally. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.60.Fi Electroluminescence

Radiative and nonradiative lifetimes in GaInN/GaN multiquantum wells

Milan S. Minsky, Satoshi Watanabe, and Norihide Yamada

J. Appl. Phys. 91, 5176 (2002); http://dx.doi.org/10.1063/1.1459106 (6 pages) | Cited 20 times

Online Publication Date: 29 March 2002

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This paper analyzes a simplified rate equation model of localized exciton emission in GaInN. Expressions for temperature dependent photoluminescence (PL) efficiency and decay time are derived and compared with time integrated (TIPL) and time resolved photoluminescence (TRPL) data for a series of multiquantum well light emitting diodes with varying In composition in the active region. Time resolved photoluminescence is measured up to relatively high temperature (540 K) and a decreasing efficiency coupled with a peak energy decay time that is weakly dependent on temperature is observed. The decay time at peak emission energy begins to decrease at a temperature that depends on the In content in the quantum wells. The analysis developed here demonstrates that application of the expressions τr=τpl/η and τnr=τpl/(1−η) is not sufficient to determine radiative and nonradiative lifetimes from TRPL and TIPL data in the GaInN system. (Here τr is the radiative decay time, τnr is the nonradiative decay time, τpl is the measured PL decay time, and η is the measured TIPL intensity normalized to the low temperature intensity.) GaInN with even small amounts of In exhibits highly efficient luminescence due to recombination through localizing centers. As relaxation occurs into both defects and localizing states after initial generation with the above GaInN band gap excitation, the number of carriers arriving at localization centers can change with temperature. This temperature dependent change should be considered when calculating relevant decay times from TRPL and TIPL data. This mechanism is distinct from an increase in the intrinsic radiative decay time obtained by applying conventional analysis to extract radiative and nonradiative lifetimes from TRPL and TIPL data. © 2002 American Institute of Physics.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.21.Fg Quantum wells
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Effects of space charge at the conjugated polymer/electrode interface

C. A. Mills, D. M. Taylor, A. Riul, and A. P. Lee

J. Appl. Phys. 91, 5182 (2002); http://dx.doi.org/10.1063/1.1454188 (8 pages) | Cited 12 times

Online Publication Date: 29 March 2002

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Films of the polymer poly(4-dicyanomethylene-4H-cyclopenta[2,1-b:3,4-b′]dithiophene (PCDM) were electrodeposited onto indium tin oxide (ITO) coated glass substrates. The formation of a polymer was confirmed by the presence of an absorption band at ∼900 nm (∼1.4 eV) previously attributed to a π–π∗ transition. Diodes formed by evaporating aluminum counterelectrodes onto the films displayed nonlinear current–voltage characteristics that were independent of voltage polarity. Interestingly, at low applied voltages, the diodes exhibited two, stable, reversible conductance states differing by about an order of magnitude. The effect is similar to that reported recently in diodes formed from chromium-doped SrZrO3. ac admittance measurements carried out over a range of frequency coupled with the voltage dependence of the device capacitance at low frequency suggests that the two states arise from the presence of a field-dependent space charge at the ITO/PCDM interface. © 2002 American Institute of Physics.
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77.22.Jp Dielectric breakdown and space-charge effects
73.61.Ph Polymers; organic compounds
85.30.Kk Junction diodes
85.65.+h Molecular electronic devices
78.66.Qn Polymers; organic compounds

Band gaps and lattice parameters of 0.9 μm thick InxGa1−xN films for 0⩽x⩽0.140

J. D. Beach, Hamda Al-Thani, S. McCray, R. T. Collins, and J. A. Turner

J. Appl. Phys. 91, 5190 (2002); http://dx.doi.org/10.1063/1.1462851 (5 pages) | Cited 9 times

Online Publication Date: 29 March 2002

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The c0 lattice parameter, band gap, and photoluminescence spectra of n-type 0.9 μm thick InxGa1−xN films with x=0, 0.045, 0.085, and 0.140 were examined. The c0 lattice parameter followed Vegard’s law using c0=0.5185 nm for GaN and c0=0.569 nm for InN. Band gap measurements by photocurrent spectroscopy fit well with data published by one other research group, with the combined set being described by the equation Eg=3.41−7.31x+14.99x2 for 0⩽x⩽0.15. Photoluminescence measurements with a pulsed nitrogen laser showed a peak well below the measured band gap, as well as significant luminescence above the measured band gap. The above-gap luminescence appears to be due to band filling by the high intensity laser pulses. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
71.20.Nr Semiconductor compounds
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Microstructural and optical properties of InAs/GaAs quantum dots embedded in modulation-doped AlxGa1−xAs/GaAs heterostructures

H. S. Lee, J. Y. Lee, T. W. Kim, D. U. Lee, D. C. Choo, M. Jung, and M. D. Kim

J. Appl. Phys. 91, 5195 (2002); http://dx.doi.org/10.1063/1.1459752 (5 pages) | Cited 6 times

Online Publication Date: 29 March 2002

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The microstructural and the optical properties of InAs/GaAs quantum-dot (QD) arrays inserted into undoped GaAs barriers embedded in an AlxGa1−xAs/GaAs were investigated by using transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images and the selected-area electron diffraction patterns showed that vertically stacked InAs QD self-assembled arrays were embedded in the GaAs barriers. The temperature-dependent PL spectra showed that the peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band of the InAs QDs shifted to lower energy with increasing temperature. The PL intensity of the InAs dots was significantly enhanced by the modulation-doped AlxGa1−xAs/GaAs heterostructure, and the thermal activation energy of the InAs dots was decreased by the addition of the modulation-doped AlxGa1−xAs/GaAs heterostructure. The present results can help to improve the understanding of the microstructural and the optical properties in InAs QD arrays inserted into GaAs barriers embedded in a modulation-doped AlxGa1−xAs/GaAs heterostructure. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
73.63.Kv Quantum dots
78.55.Cr III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.37.Lp Transmission electron microscopy (TEM)
73.20.At Surface states, band structure, electron density of states

Avalanche breakdown voltage of In0.53Ga0.47As

J. S. Ng, J. P. R. David, G. J. Rees, and J. Allam

J. Appl. Phys. 91, 5200 (2002); http://dx.doi.org/10.1063/1.1462845 (3 pages) | Cited 13 times

Online Publication Date: 29 March 2002

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Avalanche breakdown voltages were determined for a series of In0.53Ga0.47As p-i-n diodes with i-region thicknesses ranging from 0.4 to 4.79 μm using measurements of reverse dark current and phase-sensitive photomultiplication. Despite its narrower bandgap In0.53Ga0.47As is found to have a very similar breakdown voltage to GaAs. © 2002 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors

Enhanced tunneling in GaN/InGaN multi-quantum-well heterojunction diodes after short-term injection annealing

A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, J. Kim, B. Luo, R. Mehandru, F. Ren, K. P. Lee, S. J. Pearton, A. V. Osinsky, and P. E. Norris

J. Appl. Phys. 91, 5203 (2002); http://dx.doi.org/10.1063/1.1465119 (5 pages) | Cited 18 times

Online Publication Date: 29 March 2002

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Multi-quantum-well GaN/InGaN heterojunction diodes prepared by metalorganic chemical vapor deposition on sapphire showed effects of strong tunneling in their I–V characteristics. The space charge region was shown to be located in the GaN/InGaN superlattice (SL). The injection of moderately high forward currents through the structure for several hours enhanced the overall tunneling through the structure and facilitated faster tunneling between the layers in the GaN/InGaN SL. These results may have relevance to the aging characteristics of light-emitting diodes under bias. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Terahertz complex mobility of hot electrons in 3C– and 6H–SiC at high temperature

E. F. Bezerra, E. W. S. Caetano, V. N. Freire, V. Lemos, J. A. P. da Costa, and E. F. da Silva

J. Appl. Phys. 91, 5208 (2002); http://dx.doi.org/10.1063/1.1464213 (5 pages)

Online Publication Date: 29 March 2002

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The complex mobility of hot electrons in 3C– and 6H–SiC at 300, 673, and 1073 K is calculated through the numerical solution of balance transport equations within a nonparabolic band picture. The electric field, applied along the hexagonal c axis or [111] direction in the cubic material, is taken as the sum of a strong variable dc (200–800 kV/cm) and a weak (20  kV/cm) ac component whose frequency is varied in the 0.1–100 THz range. The real electron mobility presents a characteristic maximum peaking around 6–10 THz, while the imaginary electron mobility presents a characteristic maximum and minimum peaking around 20–40 THz and 2–5 THz, respectively. At the highest lattice temperature explored, the electron complex mobilities for both hexagonal and cubic SiC polytypes have nearly similar frequency dependent patterns. © 2002 American Institute of Physics.
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72.30.+q High-frequency effects; plasma effects
72.80.Jc Other crystalline inorganic semiconductors
72.20.Ht High-field and nonlinear effects
73.50.Mx High-frequency effects; plasma effects
73.50.Fq High-field and nonlinear effects

Coulomb blockade effects and conduction mechanism in extremely thin polycrystalline-silicon wires

Kensaku Kawamura, Toshirou Kidera, Anri Nakajima, and Shin Yokoyama

J. Appl. Phys. 91, 5213 (2002); http://dx.doi.org/10.1063/1.1464650 (8 pages) | Cited 5 times

Online Publication Date: 29 March 2002

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Narrow (⩾95 nm) and extremely thin (∼7 nm) heavily phosphorous-doped polycrystalline-silicon (poly-Si) wires were fabricated by low-pressure chemical vapor deposition. The electrical conduction mechanism has been investigated at low temperatures (down to ∼5 K), and observation by transmission electron microscopy (TEM) was carried out. Single-electron effects such as Coulomb oscillations have been observed at temperatures up to 80 K. The size of the island in the poly-Si wires was estimated from the electrical properties, and it was in the same order as the grain size of the poly-Si measured by TEM. A maximum tunnel barrier height of ∼26 meV of the poly-Si grain boundary is obtained from the temperature dependence of the conductance of the sample. A model for the electronic conduction through multiple islands was proposed from the width dependence of their electrical properties. © 2002 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.63.Bd Nanocrystalline materials
73.61.Cw Elemental semiconductors

Current and voltage noise in WO3 nanoparticle films

A. Hoel, L. K. J. Vandamme, L. B. Kish, and E. Olsson

J. Appl. Phys. 91, 5221 (2002); http://dx.doi.org/10.1063/1.1423398 (6 pages) | Cited 10 times

Online Publication Date: 29 March 2002

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Current and voltage noise measurements have been carried out on nanoparticle WO3 films. The fluctuation dissipation theorem holds, which indicates that the observed noise is an equilibrium phenomenon. Results on the thinnest films show that noise measurements can be used for quality assessment of nanocrystalline insulating films. © 2002 American Institute of Physics.
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73.63.Bd Nanocrystalline materials
73.61.Ng Insulators
72.70.+m Noise processes and phenomena
73.50.Td Noise processes and phenomena
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