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15 Oct 2003

Volume 94, Issue 8, pp. 4743-5438

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Optical, photoelectric, and photorefractive properties of Ti-doped CdTe crystals

Yu. P. Gnatenko, A. O. Borshch, N. Kukhtarev, T. Kukhtareva, I. O. Faryna, V. I. Volkov, P. M. Bukivskij, R. V. Gamernyk, V. I. Rudenko, S. Yu. Paranchych, and L. D. Paranchych

J. Appl. Phys. 94, 4896 (2003); http://dx.doi.org/10.1063/1.1610787 (8 pages) | Cited 9 times

Online Publication Date: 30 September 2003

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The photorefractive characteristics of Ti-doped CdTe semi-insulating crystals were measured. Additional optical and photoelectric measurement confirmed that titanium has advantages over other dopants and that this material has better characteristics for potential applications. The high optical holographic gain coefficient, Γ≈0.60 cm−1, low background absorption, kb≈0.2 cm−1, high optical quality and homogeneity, and almost monopolar (electronic) photoconductivity show that these materials can be effectively used for both optical and photoelectric applications in the near infrared region. Studies of the optical absorption and photodiffusion current made it possible to determine the nature and energy structure of impurity and intrinsic defects as well as to establish their role in the photorefractive effect. It is shown that the excited impurity 4T1(F) state is in resonance with the conduction band. As a result, autoionization of electrons to the conduction band under laser excitation takes place. An energy-level diagram, both of impurity and intrinsic defects, in the CdTe:Ti crystals was constructed. © 2003 American Institute of Physics.
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78.20.-e Optical properties of bulk materials and thin films
72.40.+w Photoconduction and photovoltaic effects
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.80.Ey III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Dose dependence of carrier and heat dynamics at an ion-implanted silicon surface measured using lens-free heterodyne transient grating method

Kenji Katayama, Masahiro Yamaguchi, and Tsuguo Sawada

J. Appl. Phys. 94, 4904 (2003); http://dx.doi.org/10.1063/1.1605255 (4 pages) | Cited 6 times

Online Publication Date: 30 September 2003

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The lens-free heterodyne transient grating method was shown to reveal the dynamics of photoexcited carriers and heat on the surface region of an ion-implanted silicon in the dose range of 1011–1015 cm−2. In addition to the fact that the detection limit of the dose was superior to that for conventional methods, several physical properties of the carrier and heat can be obtained by analyzing transient responses. Theoretical analysis provided the lifetime of carriers and thermal diffusion coefficients in the ion-implanted surface region. © 2003 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
66.30.Xj Thermal diffusivity
72.80.Cw Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.82.Fk Semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.47.-p Spectroscopy of solid state dynamics

Viscosity and elastic constants of thin films of amorphous Te alloys used for optical data storage

J. Kalb, F. Spaepen, T. P. Leervad Pedersen, and M. Wuttig

J. Appl. Phys. 94, 4908 (2003); http://dx.doi.org/10.1063/1.1610775 (5 pages) | Cited 24 times

Online Publication Date: 30 September 2003

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The biaxial modulus and the linear coefficient of thermal expansion of sputtered amorphous Ge4Sb1Te5, Ge2Sb2Te5, and Ag0.055In0.065Sb0.59Te0.29 thin films were determined from stress versus temperature measurements on two different substrates. Viscous flow was measured by stress relaxation at constant temperature using wafer curvature measurements. The shear viscosity increased linearly with time, which can be attributed to bimolecular structural relaxation kinetics. The isoconfigurational activation energy was 1.94±0.09 eV for Ge4Sb1Te5, 1.76±0.05 eV for Ge2Sb2Te5, and 1.33±0.09 eV for AgInSbTe. These values scale with the absolute melting temperatures of the material. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
42.70.Ln Holographic recording materials; optical storage media
62.20.D- Elasticity
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Dv Thermal stability; thermal effects

Capillary condensation monitored in birefringent porous silicon layers

N. Künzner, E. Gross, J. Diener, D. Kovalev, V. Yu. Timoshenko, and D. Wallacher

J. Appl. Phys. 94, 4913 (2003); http://dx.doi.org/10.1063/1.1609643 (5 pages) | Cited 8 times

Online Publication Date: 30 September 2003

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We performed studies on the capillary condensation of various substances in optically anisotropic porous silicon layers. Their strong in-plane form birefringence has been utilized to analyze the polarization state of the transmitted light when molecules penetrate into the pores. The polarization state of the transmitted light is correlated with the filling fraction of the pores by an effective-medium model for anisotropic porous materials. The experimentally obtained adsorption/desorption isotherms show hysteresis typical for capillary condensation in porous materials. We discuss the shape of the hysteresis loops in the framework of the morphology of the layers. Pore-size distributions derived from adsorption/desorption isotherms are presented. © 2003 American Institute of Physics.
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78.20.Fm Birefringence
78.66.Db Elemental semiconductors and insulators
68.43.Mn Adsorption kinetics

Configurations, energies, and thermodynamics of the neutral MgH complex in GaN

A. F. Wright and S. M. Myers

J. Appl. Phys. 94, 4918 (2003); http://dx.doi.org/10.1063/1.1610232 (5 pages) | Cited 10 times

Online Publication Date: 30 September 2003

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Atomic configurations corresponding to local-energy minima for the neutral MgH complex in wurtzite GaN are identified using density-functional theory and the generalized-gradient approximation for exchange and correlation. MgH binding energies, H local-mode vibration frequencies, and configurational degeneracies for the six lowest-energy configurations are used, along with corresponding results for isolated H+, to compute equilibrium H state populations in Mg-doped GaN as a function of temperature. For a Mg concentration of 1×1019/cm3 and a H/Mg concentration ratio of 0.99, MgH is found to be the majority H species at room temperature with isolated H+ becoming the majority species at T≈550 °C. Among the MgH states, one is found to dominate at all temperatures. The dominant configuration consists of H at an antibonding site of a N neighbor of the substitutional Mg, with the Mg–N and N–H bonds nearly aligned and the N–H bond oriented at an angle of ∼109° with the c axis. The H stretch-mode frequency of the dominant state is consistent with the peak observed in Fourier-transform infrared reflection spectra from Mg-doped GaN samples. © 2003 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
71.55.Eq III-V semiconductors
71.15.Nc Total energy and cohesive energy calculations
78.30.Fs III-V and II-VI semiconductors
61.50.Lt Crystal binding; cohesive energy
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Anisotropy of optical properties of conjugated polymer thin films by spectroscopic ellipsometry

Maria Losurdo, Giovanni Bruno, and Eugene A. Irene

J. Appl. Phys. 94, 4923 (2003); http://dx.doi.org/10.1063/1.1610236 (7 pages) | Cited 13 times

Online Publication Date: 30 September 2003

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Optical properties of thin films of conjugated poly(arylenephenylene) polymers have been determined using variable angle spectroscopic ellipsometry. Dispersion of the complex refractive index parallel, N∥=(n∥+ik∥), and perpendicular, N⊥=(n⊥+ik⊥), to the film plane are reported for the photon energy range 1.5–5.0 eV. The energy dispersion in the optical properties has been analyzed using a three-phase model and Lorentzian dispersion functions for the polymers. The resonant frequencies of the Lorentzian oscillators describe the fundamental π-π∗ optical transition polarized parallel to the polymer chain and indicate additional optical transitions polarized perpendicular to the polymer chain that are introduced by interchain interactions. Dependence of the optical anisotropy and fundamental π-π∗ optical transition on the polymer backbone is discussed. © 2003 American Institute of Physics.
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78.66.Li Other semiconductors
78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Temperature dependence of the radiative recombination coefficient of intrinsic crystalline silicon

T. Trupke, M. A. Green, P. Würfel, P. P. Altermatt, A. Wang, J. Zhao, and R. Corkish

J. Appl. Phys. 94, 4930 (2003); http://dx.doi.org/10.1063/1.1610231 (8 pages) | Cited 47 times

Online Publication Date: 30 September 2003

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The radiative recombination coefficient B(T) of intrinsic crystalline silicon is determined as a function of temperature over the temperature range 77–300 K. We observe that B(T) decreases as a function of temperature and we compare our results to previously published contradictory data from the literature. The radiative recombination coefficient is calculated from the absorption coefficient for band-to-band transitions, which we determine at different temperatures from photoluminescence spectra measured on planar high resistivity float zone silicon wafers. Photoluminescence spectra could be detected over a large range of more than five orders of magnitude, which allowed us to determine extremely low values of the absorption coefficient in the spectral range where absorption processes are accompanied by the simultaneous absorption of up to four phonons. © 2003 American Institute of Physics.
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71.20.Mq Elemental semiconductors
78.55.Ap Elemental semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Modeling plate impact response of particle–polymer composite

Duan Z. Zhang

J. Appl. Phys. 94, 4938 (2003); http://dx.doi.org/10.1063/1.1610235 (8 pages) | Cited 3 times

Online Publication Date: 30 September 2003

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A recently obtained constitutive relation [Zhang et al., Phys. Rev. E 66, 051806 (2002)] is used for polymers to model plate impact experiments on a composite material consisting of elastic particles and a polymer binder. The stress relaxation in the polymer is described by a kernel in a history integral. The kernel implies a 1/math stress relaxation for a short time t, and an exponential stress relaxation for a long time. It is found that the binder behavior, especially the stress relaxation at a short-time scale, plays an essential role in the wave dispersion observed during the experiments. Although it is difficult to implement the history dependent constitutive relation directly into a numerical calculation, a mathematical approximation of the kernel is found in the form resembling a prony series. The approximation enables easy implementation of the constitutive relation into numerical calculations. While the conventional use of a prony series requires a series of experiments to determine the parameters, in the present article, the parameters in the series expansion are uniquely determined by the kernel. Furthermore, not all the terms in the series are needed for a specific problem of interest. Only those terms with the relaxation times in the range of the time scales of the physical process are important. © 2003 American Institute of Physics.
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46.55.+d Tribology and mechanical contacts
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Influence of local heating on micro-Raman spectroscopy of silicon

S. Kouteva-Arguirova, Tz. Arguirov, D. Wolfframm, and J. Reif

J. Appl. Phys. 94, 4946 (2003); http://dx.doi.org/10.1063/1.1611282 (4 pages) | Cited 14 times

Online Publication Date: 30 September 2003

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In micro-Raman spectroscopy strong local heating by the tightly focused laser beam results in an unexpectedly small temperature shift of the Raman peak. The experimental results of shift, broadening, and asymmetry are discussed in view of restricted thermal expansion and a temperature dependent Raman cross section. The Raman signal originates mostly in the wings of the beam profile, where the temperature is substantially lower than at the center. Consequently, the Raman peak shift cannot be used to estimate the maximal surface temperature: despite local melting in the center of the probed spot, the maximal detected shift is only about 2 cm−1, 10 times less than expected from the center temperature. © 2003 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators

Transient enhanced diffusion of arsenic in silicon

S. Solmi, M. Ferri, M. Bersani, D. Giubertoni, and V. Soncini

J. Appl. Phys. 94, 4950 (2003); http://dx.doi.org/10.1063/1.1609640 (6 pages) | Cited 29 times

Online Publication Date: 30 September 2003

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The transient enhanced diffusion (TED) of As in silicon samples implanted at 35 keV with dose 5×1015 cm−2 has been investigated in the temperature range between 750 and 1030 °C by comparing experimental and simulated profiles. For temperatures higher than 900 °C the phenomenon is of modest entity and vanishes after a few seconds, whereas at lower temperatures diffusivity enhancements of some order of magnitude have been observed. The anomalous shift of the junction depth, evaluated at 2×1018 cm−3, is about 12 nm at 900 °C and increases up to 45 nm at 750 °C. It has been verified that the two are the contributions, that generate the interstitial excess responsible for the TED: (i) the implantation damage and (ii) the aggregation in clusters of the As atoms. From an experiment that allows us to separate the two contributions, we estimate that about one third of the TED observed in the first 20 min of annealing at 800 °C is due to the defects produced by clustering. The influence of clustering on the shape of the As profiles after diffusion at different temperatures is also discussed. © 2003 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
61.72.S- Impurities in crystals
61.72.J- Point defects and defect clusters

Transition metal ion implantation into AlGaN

R. M. Frazier, G. T. Thaler, C. R. Abernathy, S. J. Pearton, M. L. Nakarmi, K. B. Nam, J. Y. Lin, H. X. Jiang, J. Kelly, R. Rairigh, A. F. Hebard, J. M. Zavada, and R. G. Wilson

J. Appl. Phys. 94, 4956 (2003); http://dx.doi.org/10.1063/1.1613375 (5 pages) | Cited 10 times

Online Publication Date: 30 September 2003

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n- and p-type AlxGa1−xN (x=0.38 for n-type, x=0.13 for p-type) layers grown on Al2O3 substrates were ion implanted with the transition metals Mn, Cr, and Co at high concentrations (peak doping levels ∼3 at. %). After implantation and annealing at 1000 °C, only impurity transitions at ∼2.9 and 3.9 eV and no band-edge photoluminescence could be observed in all the samples. X-ray diffraction did not detect any peaks associated with second phase formation. Room-temperature hysteresis loops were obtained for Co-implanted n-type AlGaN, while there was no convincing evidence for ferromagnetism in the Mn- or Cr-implanted n-AlGaN. By sharp contrast, Mn implantation in p-AlGaN did produce ferromagnetic behavior and 300 K hysteresis. Both carrier type and crystalline quality can influence the resulting magnetic properties. © 2003 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Time resolved dynamics of rapid melting and resolidification of Sb thin films under ns and ps laser pulse irradiation

S. M. Wiggins, W. M. Gawelda, J. Solis, R. Serna, and C. N. Afonso

J. Appl. Phys. 94, 4961 (2003); http://dx.doi.org/10.1063/1.1609635 (6 pages) | Cited 4 times

Online Publication Date: 30 September 2003

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Real time reflectivity measurements with ps time resolution at the wavelength λ=514.5 nm have been used to analyze the rapid melting and solidification dynamics of Sb thin films on glass substrates irradiated with a visible laser pulse (λ=583 nm) of duration either 30 ps or 2 ns. Significant differences in the solidification dynamics have been obtained for the three different film thickness investigated (25, 50, and 200 nm) as well as between ps and ns laser pulse excitation. Bulk solidification is the dominant mechanism observed at high laser fluence in the thinner films, no matter the pulse duration used, while interfacial solidification is the only mechanism observed in the thicker film for both pulse durations. These results have been interpreted in terms of the differences of the effective thermal conductivity of the films. The comparison of the behavior of these films with the case of Sb-rich GeSb ones makes it clear that relatively minor changes in the film composition can lead to big changes in the solidification dynamics under similar heat flow conditions that are beneficial for the application of such films in phase change optical recording with ultrashort pulses. The optical properties of molten phase of Sb and of the solid material at the melting temperature have been also been determined at 514.5 nm. © 2003 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.55.Nq Composition and phase identification
78.47.-p Spectroscopy of solid state dynamics
64.70.D- Solid-liquid transitions
78.66.Bz Metals and metallic alloys

Nanofluids containing multiwalled carbon nanotubes and their enhanced thermal conductivities

Huaqing Xie, Hohyun Lee, Wonjin Youn, and Mansoo Choi

J. Appl. Phys. 94, 4967 (2003); http://dx.doi.org/10.1063/1.1613374 (5 pages) | Cited 173 times

Online Publication Date: 30 September 2003

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Multiwalled carbon nanotubes (CNTs) as produced are usually entangled and not ready to be dispersed into fluids. We treated CNTs by using a concentrated nitric acid to disentangle CNT aggregates for producing CNT nanofluids. Oxygen-containing functional groups have been introduced on the CNT surfaces and more hydrophilic surfaces have been formed during this treatment, which enabled to make stable and homogeneous CNT nanofluids. Treated CNTs were successfully dispersed into polar liquids like distilled water, ethylene glycol without the need of surfactant and into nonpolar fluid like decene with oleylamine as surfactant. We measured the thermal conductivities of these nanotube suspensions using a transient hot wire apparatus. Nanotube suspensions, containing a small amount of CNTs, have substantially higher thermal conductivities than the base fluids, with the enhancement increasing with the volume fraction of CNTs. For the suspensions with the same loading, the enhanced thermal conductivity ratios are reduced with the increasing thermal conductivity of the base fluid. Comparison between the experimental data and the theoretical model indicates that the thermal conductivities of nanotube suspensions seem to be very dependent on the interfacial layer that exists between the nanotube and the liquid. © 2003 American Institute of Physics.
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66.25.+g Thermal conduction in nonmetallic liquids
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
82.70.Kj Emulsions and suspensions
61.46.-w Structure of nanoscale materials

Ab initio study of 3C inclusions and stacking fault–stacking fault interactions in 6H-SiC

H. P. Iwata, U. Lindefelt, S. Öberg, and P. R. Briddon

J. Appl. Phys. 94, 4972 (2003); http://dx.doi.org/10.1063/1.1610772 (8 pages) | Cited 9 times

Online Publication Date: 30 September 2003

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Ab initio supercell calculations of cubic inclusions in 6H-SiC are performed. The cubic inclusions can be created in perfect 6H-SiC by the propagation of successive partial dislocations having the same Burgers vector in neighboring basal planes, i.e., multiple stacking faults. We have studied the electronic structures and the total energies of 6H-SiC single crystals that contain one, two, three, and four stacking faults, based on density functional theory in local density approximation. Our total energy calculations have revealed that the second stacking fault energy in 6H-SiC is about six to seven times larger than that of an isolated stacking fault, which is actually opposite the trend recently obtained for 4H-SiC [J. Appl. Phys. 93, 1577 (2003)]. The effects of spontaneous polarization on the electronic properties of stacking disorders are examined in detail. The calculated positions of the quantum-well-like localized bands and stacking fault energies of 3C inclusions in 6H-SiC are compared with those previously determined in 4H-SiC, and the possibility of local hexagonal to cubic polytypic transformations is discussed in light of the formation energy and quantum-well action. © 2003 American Institute of Physics.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
71.20.Nr Semiconductor compounds
77.22.Ej Polarization and depolarization
71.15.Nc Total energy and cohesive energy calculations
71.55.Ht Other nonmetals
61.72.Nn Stacking faults and other planar or extended defects
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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Low-temperature GaAs films grown on Ge and Ge/SiGe/Si substrates

C. L. Andre, J. J. Boeckl, C. W. Leitz, M. T. Currie, T. A. Langdo, E. A. Fitzgerald, and S. A. Ringel

J. Appl. Phys. 94, 4980 (2003); http://dx.doi.org/10.1063/1.1610243 (6 pages) | Cited 4 times

Online Publication Date: 30 September 2003

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The growth and structural properties of low-temperature GaAs (LT-GaAs) films grown on Ge/SiGe/Si substrates using solid-source molecular-beam epitaxy were investigated. Identical structures were also grown on both Ge and GaAs substrates in order to ascertain the effects of heterovalent interfaces, lattice mismatch, and surface morphology on the structural properties and excess As incorporation of LT-GaAs. Triple-axis x-ray diffraction measurements revealed nearly identical lattice expansion due to excess As incorporation for LT-GaAs layers on all substrates, with the excess As concentration estimated to be 0.34%. Subsequent in situ annealing resulted in complete layer relaxation coupled with the formation of randomly distributed As precipitates of similar sizes throughout the LT-GaAs layers on each substrate as determined by transmission electron microscopy. Secondary ion mass spectroscopy measurements confirmed the incorporation of excess As to be identical for growth on each substrate type, indicating that LT-GaAs with ideal structural properties can be grown on compositionally graded SiGe/Si substrates with no apparent impact from crosshatched surface morphology or heterovalent interfaces. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.Nq Composition and phase identification
61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria

Fokker–Planck approach to extending the one-flux method of carrier transport in semiconductors to variable energies

W. R. McKinnon

J. Appl. Phys. 94, 4986 (2003); http://dx.doi.org/10.1063/1.1610233 (9 pages) | Cited 2 times

Online Publication Date: 30 September 2003

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The one-flux method of McKelvey, Longini, and Brody [Phys. Rev. 123, 51 (1961)] is extended to arbitrary distributions of the fluxes in energy, based on a Fokker–Planck approach to the Boltzmann equation. The method is used to discuss the backscattering of carriers from a high-field region. It is shown that a key result of the one-flux method, that the backscattering vanishes in the limit of high fields, holds more generally than under the assumptions of the one-flux method. © 2003 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Temperature dependent contactless electroreflectance study of intersubband transitions in a self-assembled InAs/InP (001) quantum dot structure

L. Malikova, Fred H. Pollak, R. A. Masut, P. Desjardins, and Lev G. Mourokh

J. Appl. Phys. 94, 4995 (2003); http://dx.doi.org/10.1063/1.1609651 (4 pages) | Cited 8 times

Online Publication Date: 30 September 2003

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Contactless electroreflectance, in the range of 18<T<300 K, has been used to investigate a self-assembled InAs/InP (001) quantum dot (QD) structure fabricated by metalorganic vapor phase epitaxy. Signals have been observed from all the relevant portions of the sample including the QDs, wetting layer, InP cap layer, and/or substrate. The energies of the QD transitions are in good agreement with an envelope function calculation based on the physical parameters of the QDs as observed from transmission electron microscopy and other relevant parameters. The temperature dependence of the energies of all transitions has been fit using both the semiempirical Varshni and Bose–Einstein-like expressions. It was found that extracted Varshni and Bose–Einstein fitting parameters are in the range of those for most III–V materials, both bulk and quantum well. However, the temperature variation for the energy transitions in the QDs is somewhat larger that reported for bulk InAs. © 2003 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.67.Hc Quantum dots
73.21.La Quantum dots
68.37.Lp Transmission electron microscopy (TEM)

Optical injection and coherent control of a ballistic charge current in GaAs/AlGaAs quantum wells

Martin J. Stevens, Ali Najmaie, R. D. R. Bhat, J. E. Sipe, H. M. van Driel, and Arthur L. Smirl

J. Appl. Phys. 94, 4999 (2003); http://dx.doi.org/10.1063/1.1609639 (6 pages) | Cited 13 times

Online Publication Date: 30 September 2003

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We report all-optical injection and coherent control of a ballistic charge current in GaAs/AlGaAs quantum wells. This current arises through quantum interference of one- and two-photon absorption of ∼100 fs pulses with parallel linear polarizations, and its magnitude can be controlled by adjusting the relative phase of the incident pulses. By monitoring differential transmission using a spatially resolved optical pump–probe technique, we observe evidence of carrier motion associated with this ballistic current. Results are consistent with a theoretical treatment specific to quantum wells, and are qualitatively similar to previous measurements in bulk GaAs. © 2003 American Institute of Physics.
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73.63.Hs Quantum wells
78.67.De Quantum wells
73.23.Ad Ballistic transport
78.47.-p Spectroscopy of solid state dynamics

Full band modeling of the excess current in a delta-doped silicon tunnel diode

Cristian Rivas, Roger Lake, William R. Frensley, Gerhard Klimeck, Phillip E. Thompson, Karl D. Hobart, Sean L. Rommel, and Paul R. Berger

J. Appl. Phys. 94, 5005 (2003); http://dx.doi.org/10.1063/1.1606114 (9 pages) | Cited 16 times

Online Publication Date: 30 September 2003

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The current of a molecular beam epitaxially grown Sb and B delta-doped Si tunnel diode is simulated in all regions of tunneling: peak, valley, and post-valley turn-on. All three regions of the I–V are qualitatively captured by the calculations. The inclusion in the model of bandtail states gives rise to the excess current and the post-valley turn on of the tunnel current. This excess current is dominated by the direct coherent tunneling component of the current tunneling from gap state to gap state. The crossover between phonon-assisted and direct occurs immediately after the valley minimum. The calculated voltages quantitatively match the experimental measurements. The magnitude of the calculated current is approximately a factor of 5.4 too small. Sources of error are analyzed. The current calculations use a second neighbor sp3s∗ planar orbital basis within the nonequilibrium Green function formalism. © 2003 American Institute of Physics.
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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

Electrical characterization of InGaN/GaN light emitting diodes grown by molecular beam epitaxy

L. Hirsch and A. S. Barrière

J. Appl. Phys. 94, 5014 (2003); http://dx.doi.org/10.1063/1.1605252 (7 pages) | Cited 25 times

Online Publication Date: 30 September 2003

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We studied the electrical behavior of multiple InGaN/GaN quantum well based light emitting diodes grown by molecular beam epitaxy and we determined three different domains of current-voltage dependence. We then described the charge carrier transport mechanisms for these three domains. The first domain, corresponding to leakage currents (V<1.5 V), takes place in the mesa side wall, in a semi-insulating material formed by air contamination, after the etching process. Below room temperature, electrical transport occurs by hopping between localized states and above room temperature by the Poole–Frenkel mechanism. The second domain, that of injection currents (1.5 V<V<3.5 V), corresponds to a hole injection from the valence band of p-GaN to the first InGaN quantum well. At low temperature (T<250 K) this hole injection is due to tunnel transfer and above 250 K to thermoionic emission. In the third domain, which corresponds to series resistor (V>3.5 V), the current is limited by the p-GaN zone. In this zone, the density of the free holes is controlled by the combined effects of the temperature and the applied forward bias. The results obtained enables the electronic states resulting from the magnesium doping to be localized at 190 meV above the valence band maximum. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.63.Hs Quantum wells
73.50.Fq High-field and nonlinear effects
73.50.Dn Low-field transport and mobility; piezoresistance

Magnetoresistance in step-edge junctions based on La0.7Sr0.3MnO3 films

A. A. Bosak, C. Dubourdieu, P. Chaudouët, J.-P. Sénateur, and T. Fournier

J. Appl. Phys. 94, 5021 (2003); http://dx.doi.org/10.1063/1.1606523 (6 pages) | Cited 3 times

Online Publication Date: 30 September 2003

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The magnetoresistance of step-edge junctions based on La0.7Sr0.3MnO3 films was investigated using a Wheatstone bridge geometry. Two types of step-edge structures were prepared: The step was either fabricated by ion-beam etching of SrTiO3 (001) substrates or by wet-chemical etching of an insulating NdMnO3 layer deposited on SrTiO3 (001). Both the magnetoresistive and insulating layers were deposited by injection-metalorganic chemical vapor deposition. The temperature dependence of the magnetoresistance was explored for both types of junctions in different field orientations. The largest low-field magnetoresistance was obtained when the step was formed directly in the substrate; it was observed up to room temperature (∼1% for an applied field of ∼0.05 T) and at 40 K, it increased ∼12% under an applied field of ∼0.1 T. The hysteretic behavior for the two types of junctions appeared to be very different. © 2003 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.My Galvanomagnetic and other magnetotransport effects
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Role of interface states in electronic properties of (ZnSe)n/(Si2)n (001) superlattices

A. Laref, H. Aourag, B. Belgoumene, and A. Tadjer

J. Appl. Phys. 94, 5027 (2003); http://dx.doi.org/10.1063/1.1605251 (8 pages) | Cited 3 times

Online Publication Date: 30 September 2003

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In a semiempirical tight-binding scheme, the detailed electronic structure and optical properties of (ZnSe)n/(Si2)n (001) superlattices (SLs) are studied with a wide range of n=1–20 giving special attention to the role of the interface states at the Zn–Si and Se–Si polar interfaces. The states at the conduction and valence-band edges are confined two dimensionally in the Si layers. Furthermore, we have found two interface bands in the lower and upper regions of the gap. The states of the lower interfaces band are located at the Zn–Si interface, while those of the upper interface band are located at the Se–Si interface. The energies of the interface states depend on the parameters representing the Zn–Si and Se–Si bond lengths and the valence band discontinuity between ZnSe and Si, but the interface states do not disappear from the gap with reasonable choices of the parameters. It is shown that the heterointerface bond relaxation strongly affects interface band in the band gap. In this system, relaxed Si bonds at the heterointerface induce a vacant interface band and a filled interface band in the band gap. By decreasing the SL period n, the energy gap between the confined band-edge states increases (2.07 eV at the Γ point for n=2) due to the quantum confinement effect. A sudden shrinkage in the band gap (Eg=1.76 eV at the M point) is obtained for n=1. The origin of the band-gap shrinkage is related to the fact that the interface states increasingly overlap and combine as band states. Furthermore, the calculated absorption spectra of the superlattices are found to be quite different from those of bulk ZnSe and Si, but fairly close to their average. © 2003 American Institute of Physics.
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73.21.Cd Superlattices
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Influence of ferromagnetic substrate on the magnetoresistance of Cr film across a nonmagnetic insulating layer

Xuesong Jin and I. V. Shvets

J. Appl. Phys. 94, 5035 (2003); http://dx.doi.org/10.1063/1.1606520 (6 pages) | Cited 1 time

Online Publication Date: 30 September 2003

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(5 nm) Cr/(x nm) MgO/Mn0.52Zn0.48Fe2O4 (MnZn spinel) substrate (1<x<7 nm), as well as (5 nm) Cr/(7 nm) MgO/glass substrate structures have been grown using molecular beam epitaxy. The influence of the MnZn spinel on the in-plane transport and magnetotransport properties of the Cr layer were studied. The existence of pinholes in the MgO layer was explored by evaluating resistance versus temperature, R(T), dependencies. A hump was observed on the R(T) curves for the MgO layer thickness (tMgO) less than 5 nm. This results from the electrical coupling between the Cr film and the MnZn spinel substrate through the pinholes in the MgO layer. A reversal of the magnetoresistance (MR) sign in Cr film was observed when tMgO is less than 7 nm. It is thought that the effect of the electrical coupling through the pinholes and the magnetostatic coupling are not the reasons for the observed negative MR. A model is proposed which suggests that the magnetic structure in the Cr film adjoining a pinhole is distorted because of the exchange coupling. Such areas in the Cr film are thought to contribute to the negative MR. © 2003 American Institute of Physics.
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75.47.Np Metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Photothermal investigations of thermal and optical properties of GaAlAsSb and AlAsSb thin layers

Faycel Saadallah, Noureddine Yacoubi, Frédéric Genty, and Claude Alibert

J. Appl. Phys. 94, 5041 (2003); http://dx.doi.org/10.1063/1.1611290 (8 pages) | Cited 9 times

Online Publication Date: 30 September 2003

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Investigation of the optical and thermal properties of GaAlAsSb/GaSb and AlAsSb/GaSb heterostructures by photothermal deflection spectroscopy (PDS) is presented. From a comparison of the amplitude and phase of the experimental PDS signal with the corresponding theoretical ones, we have determined the thermal conductivities and thickness, as well as the variations versus wavelength of the optical absorption coefficients and refractive indices of the GaAlAsSb and AlAsSb layers. The refractive indices measured in the transparency region and the small values of the thermal conductivity are in good agreement with theoretical interpolation reported in previous literature. © 2003 American Institute of Physics.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Intersubband absorption in V-groove quantum wires

Dejan M. Gvozdić and Andreas Schlachetzki

J. Appl. Phys. 94, 5049 (2003); http://dx.doi.org/10.1063/1.1610804 (4 pages) | Cited 4 times

Online Publication Date: 30 September 2003

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This article describes intersubband optical transitions in V-groove quantum wires and the resulting absorption. It is demonstrated that the optical absorption spectrum can be modified and controlled by varying the quantum wire dimensions. In addition, the importance of the conduction band nonparabolicity in calculating the absorption spectrum is pointed out. Finally, a possible application of this structure as a converter to the far-infrared wavelength range is discussed. © 2003 American Institute of Physics.
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78.67.Lt Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
73.21.Hb Quantum wires
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