By Topic

Journal of Applied Physics

Issue 8 • Date Apr 2002

Filter Results

Displaying Results 1 - 25 of 124
  • Issue Cover

    Page(s): c1
    Save to Project icon | PDF file iconPDF (35 KB)  
    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (207 KB)  
    Freely Available from IEEE
  • Transmission spectroscopy of photonic crystal based waveguides with resonant cavities

    Page(s): 4791 - 4794
    Save to Project icon | PDF file iconPDF (349 KB)  

    Photonic crystal waveguides including resonant cavities have been fabricated and investigated by transmission spectroscopy. The waveguides consist of two missing rows in a triangular lattice of air holes in a GaAs/AlGaAs slab–waveguide structure. The mirrors of the cavities are formed by adding two rows of holes perpendicular to the guiding direction inside the waveguide. The spectrally broad photoluminescence of an InAs quantum dot layer in the heterostructure is used to probe the transmission. Depending on the resonator size, characteristic resonant peaks are observed in the transmission spectra. Finite difference time domain calculations of the transmission of the investigated structures show good agreement with experimental data. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • In situ shrinkage measurement of holographic polymer dispersed liquid crystals

    Page(s): 4795 - 4800
    Save to Project icon | PDF file iconPDF (324 KB)  

    The formation dynamics of reflective holographic polymer dispersed liquid crystals (H-PDLCs) is investigated with in situ spectroscopy. A modified diffusion model is proposed to describe the time dependent shrinkage of the polymer matrix during formation. The relationship between polymer shrinkage and functionality in H-PDLC systems is found to be linear. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Interdiffusion-based optimal quantum-well profile shaping for unipolar quantum-fountain lasers

    Page(s): 4801 - 4805
    Save to Project icon | PDF file iconPDF (78 KB)  

    A method is described for the design and realization of quantum-well (QW) structures optimized in respect to gain in optically pumped intersubband lasers. It relies on finding the optimal smooth potential (QW profile) by employing supersymmetric quantum mechanics, and then using the simulated annealing method to design a suitable QW structure with a small number of layers of different composition, such that it delivers the closest approximate to the optimal smooth profile after the interdiffusion process. This route towards achieving optimal QW profiles should be much easier to apply than a direct modulation of material composition at time of growing the structure. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurement of Ar metastables near a dielectric surface in barrier and plasma display panel discharges

    Page(s): 4806 - 4810
    Save to Project icon | PDF file iconPDF (123 KB)  

    The density of Ar 1s5 metastable excited atoms in the vicinity of a surface in barrier and display panel discharges was measured by the laser-induced evanescent-mode fluorescence technique. The temporal and spatial distributions of excited atoms were also measured by conventional spontaneous emission and laser absorption methods. From these measurements at various pressures, the behavior of the metastable atoms is clarified and the flux of the metastable atoms on the barrier surface is estimated. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Determination of the ionization and acceleration zones in a stationary plasma thruster by optical spectroscopy study: Experiments and model

    Page(s): 4811 - 4817
    Save to Project icon | PDF file iconPDF (712 KB)  

    A stationary plasma thruster is experimentally studied using different optical spectroscopies of xenon ions. Doppler shift in laser induced fluorescence is used for velocity determination while the ion density is determined by emission spectroscopy. These experiments show unambiguously that the ionization and the acceleration zones are spatially distinct inside the thruster channel. Moreover, it is shown that these results can be easily taken into account with a very simple quasineutral stationary one-dimensional model. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ion extraction from a laser-ionized plasma produced between parallel plate cathodes and an anode above them

    Page(s): 4818 - 4823
    Save to Project icon | PDF file iconPDF (105 KB)  

    We studied the behavior of a laser-photoionized plasma in atomic-vapor laser isotope separation under an external electric field with a two-dimensional one-fluid model, in which electrons are assumed to be in thermal equilibrium. Sheath-formation and ion-extraction processes are investigated in both a conventional parallel-electrode system and an M-type electrode system consisting of two parallel cathodes and one anode above them. The process of ion extraction in the M-type electrode was made clear and it is shown that ions are collected twice as fast as in the parallel-electrode system. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ion flux from vacuum arc cathode spots in the absence and presence of a magnetic field

    Page(s): 4824 - 4832
    Save to Project icon | PDF file iconPDF (306 KB)  

    Because plasma production at vacuum cathode spots is approximately proportional to the arc current, arc current modulation can be used to generate ion current modulation that can be detected far from the spot using a negatively biased ion collector. The drift time to the ion detector can used to determine kinetic ion energies. A very wide range of cathode materials have been used. It has been found that the kinetic ion energy is higher at the beginning of each discharge and approximately constant after 150 μs. The kinetic energy is correlated with the arc voltage and the cohesive energy of the cathode material. The ion erosion rate is in inverse relation to the cohesive energy, enhancing the effect that the power input per plasma particle correlates with the cohesive energy of the cathode material. The influence of three magnetic field configurations on the kinetic energy has been investigated. Generally, a magnetic field increases the plasma impedance, arc burning voltage, and kinetic ion energy. However, if the plasma is produced in a region of low field strength and streaming into a region of higher field strength, the velocity may decrease due to the magnetic mirror effect. A magnetic field can increase the plasma temperature but may reduce the density gradients by preventing free expansion into the vacuum. Therefore, depending on the configuration, a magnetic field may increase or decrease the kinetic energy of ions. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Experimental study on the feasibility of hot plasmas as stripping media for MeV heavy ions

    Page(s): 4833 - 4839
    Save to Project icon | PDF file iconPDF (235 KB)  

    The feasibility of using hot plasmas as strippers for low-energy ion beams has been investigated by measuring charge state distributions of 350 keV/u ions (12C,16O,19F) after their passage through a laser-produced plasma target. The plasma target was produced by irradiating a small pellet of lithium hydride with a Nd-glass laser. The profiles of electron densities of the plasma target were estimated from the intensity profiles of an Ar laser refracted by the plasma. The intensities of ions with different charge states were simultaneously measured using a time-resolved magnetic spectrograph. It was found that this plasma can yield higher charge states than conventional gaseous or solid strippers. Results of a numerical analysis are compared with the experimental data to explain the observed stripping capability of the plasma. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Advantages of the “optical cavity substrate” for real time infrared spectroscopy of plasma–surface interactions

    Page(s): 4840 - 4845
    Save to Project icon | PDF file iconPDF (89 KB)  

    Infrared reflectance spectroscopy can be used to analyze surface reactions during the plasma processing of thin films via the characteristic absorption modes of chemical bonds. However, infrared absorption is a relatively weak effect: to detect a submonolayer quantity of adsorbed or near-surface species in real time, the optical sensitivity must be enhanced in order to produce a measurable reflectance change. This article presents the use of a optically resonant dielectric stack, called an optical cavity substrate, to provide this sensitivity enhancement, and compares this approach quantitatively to other substrate/beam combinations. The optical cavity substrate provides several advantages: (i) a large signal enhancement for both bulk and surface vibrational modes, which is nearly independent of the film refractive index n and thickness up to ∼20 nm, (ii) a large signal enhancement for interfaces buried under thick films, and (iii) a relatively constant baseline signal, which simplifies the data analysis. To demonstrate the power of the optical cavity substrate, we analyze the growth of hydrogenated amorphous silicon in real time. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spectroscopic properties of Co2+ in related spinels

    Page(s): 4846 - 4852
    Save to Project icon | PDF file iconPDF (77 KB)  

    We report the absorption and fluorescence spectra of divalent cobalt (Co2+) in a series of related spinels Mg(1-x)CoxAlBOC, where B=2, 4, 6, C=4, 7, 10, and x represents the amount of Co2+ that substitutes for Mg2+ in tetrahedral sites of Td symmetry. The spectra support the assumption that both Mg2+ and Co2+ prefer the tetrahedral cation sites during the growth of these crystalline materials. These observations also support earlier conclusions obtained from crystallographic and thermodynamic studies of the MgO and Al2O3 phase diagram. The observed spectra are analyzed and compared to calculated electronic levels derived from lattice-sum models using crystallographic data determined from the crystals grown in the present studies. Comments are made in relevance to the use of these crystals as saturable absorbers for near infrared Q-switched lasers. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Generation and annihilation of boron–oxygen related defects in boron-doped Czochralski-grown Si solar cells

    Page(s): 4853 - 4856
    Save to Project icon | PDF file iconPDF (59 KB)  

    Defects that reduce the minority-carrier lifetime in silicon crystal are produced by minority-carrier injection (forward bias or light illumination) when the boron-doped Czochralski-grown silicon (Cz-Si) is used as a solar cell material. The number of induced defects is determined from changes in open-circuit voltage (VOC) of the cells. It increases with the carrier injection time, and then becomes saturated. The saturated value increases as the ambient temperature increases, during the carrier injection. These defects are observed to be vanished by thermal annealing at 200 °C for 20 min, indicating that they are in an unstable state and that some of them are annihilated even during the carrier injection. Therefore, the total number of induced defects to be determined by the difference between the generation and the annihilation rates. The activation energies for the generation process and annihilation process are evaluated to be 0.77 eV and 0.32 eV, respectively. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Anisotropic elastic-stiffness coefficients of an amorphous Ni–P film

    Page(s): 4857 - 4862
    Save to Project icon | PDF file iconPDF (108 KB)  

    This study presents a complete set of effective elastic-stiffness coefficients of a Ni80P20 amorphous-alloy thin film deposited on an aluminum-alloy substrate by electroless plating. The film thickness was 12 μm. The electromagnetic-acoustic-resonance method detected resonance frequencies of the triple-layered specimens (film/substrate/film), which enabled us to determine all five independent elastic-stiffness coefficients of the film using known substrate elastic properties. The resulting coefficients were those of a transverse isotropic material. There was strong anisotropy between the in-plane and normal directions; the in-plane Young’s modulus is larger than the normal Young’s modulus by 34%, for example. The anisotropic coefficients can be interpreted by considering a micromechanics model for local incomplete cohesion (thin ellipsoidal voids) aligned parallel to the film surface. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Temperature stability of sputtered niobium–oxide films

    Page(s): 4863 - 4871
    Save to Project icon | PDF file iconPDF (154 KB)  

    The effect of annealing temperature on the structural and optical properties of sputtered niobium–oxide films has been investigated. The temperature dependence of structure, density, and optical constants has been studied by Rutherford backscattering, x-ray diffraction, x-ray reflection, optical spectroscopy, and variable angle spectroscopic ellipsometry techniques. Rutherford backscattering measurements show no variation in the stoichiometry of the films upon annealing of amorphous Nb2O5 films, while amorphous NbO is oxidized to Nb2O5. X-ray diffraction studies show that as-deposited films are amorphous and only crystallize at around 500 °C. X-ray reflectivity studies reveal a continuous increase of film density with increasing annealing temperature. Optical spectroscopy and spectroscopic ellipsometry confirm that the refractive index n and the band gap Eg increase upon increasing annealing temperature. The variation of the refractive index with density of the niobium–oxide films is observed to follow the Clausius–Mossotti relation and the molecular electronic polarizability has been deduced from the straight line fit of Lorentz–Lorentz law. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Full characterization of the interface between the organic semiconductor copper phthalocyanine and gold

    Page(s): 4872 - 4878
    Save to Project icon | PDF file iconPDF (164 KB)  

    We present a study of the interface properties of the molecular organic semiconductor copper phthalocyanine (CuPC) on single crystalline as well as polycrystalline Au using photoemission spectroscopy. Despite the different orientation of the molecules on the two substrates, the observed energy level alignment is identical. We observe the formation of an interface dipole while band bending is very small. In addition, we have carried out complementary studies of the CuPC/GeS(001) interface to pin down photoemission final state effect contributions to the observed energy level shifts. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Calculation of thermodynamic, electronic, and optical properties of monoclinic Mg2NiH4

    Page(s): 4879 - 4885
    Save to Project icon | PDF file iconPDF (173 KB)  

    Ab initio total-energy density functional theory is used to investigate the low temperature (LT) monoclinic form of Mg2NiH4. The calculated minimum energy geometry of LT Mg2NiH4 is close to that determined from neutron diffraction data, and the NiH4 complex is close to a regular tetrahedron. The enthalpies of the phase change to high temperature (HT) pseudo-cubic Mg2NiH4 and of hydrogen absorption by Mg2Ni are calculated and compared with experimental values. LT Mg2NiH4 is found to be a semiconductor with an indirect band gap of 1.4 eV. The optical dielectric function of LT Mg2NiH4 differs somewhat from that of the HT phase. A calculated thin film transmittance spectrum is consistent with an experimental spectrum. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effects of fluorine on structure, structural relaxation, and absorption edge in silica glass

    Page(s): 4886 - 4890
    Save to Project icon | PDF file iconPDF (111 KB)  

    The effects of fluorine (F) doping on silica glass structure, structural relaxations, and vacuum ultraviolet (VUV) absorption edge were investigated by the infrared and vacuum ultraviolet absorption measurements. Linewidth of 2260 cm-1 absorption band, which is one of the good indicators of structural disorder, decreases proportionally to the fictive temperature (Tf). On the other hand, it is irrespective of F concentration. Structural relaxations are strongly stimulated by F doping. The transparency near the absorption edge depends on both F concentration and Tf. When Tf is constant, absorption edge shifts to a shorter wavelength proportionally to the F concentration. These results strongly suggest that there are two main factors that control the VUV absorption edge of F-doped silica glass; band gap widening by increasing Si–F bond and reduction of structural disorder. The latter factor is not directly caused by structural change by F doping. F enhances the structural relaxation, and it is easy to obtain samples with lower Tf, resulting in reducing structural disorder. Furthermore, a way to determine Tf of F-doped silica glass is offered. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Acceptor diffusion and segregation in (AlxGa1-x)0.5In0.5P heterostructures

    Page(s): 4891 - 4899
    Save to Project icon | PDF file iconPDF (133 KB)  

    Acceptor segregation is investigated as a function of compositional difference, Δx, between adjacent layers in (AlxGa1-x)0.5In0.5P heterostructures. Magnesium, Zn, Be, and Mn acceptor species are all shown to segregate out of the high band gap Al-rich (AlxGa1-x)0.5In0.5P layers and into the low band gap Al-poor (AlxGa1-x)0.5In0.5P layers during high temperature epitaxial growth of such heterostructures. The observed acceptor segregation appears to be independent of growth method or dopant incorporation method (metalorganic chemical vapor deposition, gas source molecular-beam epitaxy, or ion implantation), and increases with increasing compositional difference between adjacent (AlxGa1-x)0.5In0.5P layers. A theoretical model is developed to describe acceptor segregation based on charge separation and the resulting electric field across the heterointerface, and the resulting acceptor segregation is shown to vary as (mh AL*/mh CL*)3/2exp(ΔEV/kT) where mh AL* and mh CL* are the hole effective masses in the active layer and confining layer, and ΔEV is the valence band offset. Comparison between experimentally measured and theoretically predict- ed acceptor segregation ratios gives excellent agreement for (AlxGa1-x)0.5In0.5P heterostructures over the range of compositional differences from Δx=0.12 to Δx=0.93. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Rapid thermal annealing of GaNxAs1-x grown by radio-frequency plasma assisted molecular beam epitaxy and its effect on photoluminescence

    Page(s): 4900 - 4903
    Save to Project icon | PDF file iconPDF (60 KB)  

    The effect of rapid thermal annealing (RTA) on GaNAs films grown on GaAs (100) substrates by radio frequency plasma-assisted solid source molecular beam epitaxy was investigated by low-temperature photoluminescence (PL) and high-resolution x-ray diffraction (HR-XRD) measurements. GaNAs samples with N content of 1.3% and 2.2% determined by experimental curve fitting of x-ray rocking curve with the dynamical diffraction theory, exhibit an overall blueshift in energy of 67.7 meV and an intermediate redshift of 42.2 meV in the PL spectra when subjected to RTA at 525–850 °C for 10 min. The results suggest that the GaNAs layer may have undergone an intermediate substitutional–interstitial diffusion in addition to purely outdiffusion of nitrogen atoms. Samples annealed at 700–750 °C showed 1.7–2.1 times improvement in integrated PL intensity and 1.6–1.8 times reduction in PL full width half maximum as compared to the as-grown sample. The HR-XRD results show no significant changes in GaNAs lattice parameter between the as-grown and annealed samples. This indicates the samples are thermally stable, with low overall nitrogen outdiffusion. The results have significant implication on the growth and postgrowth treatment of GaNAs material for high performance optoelectronic device application. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Photoreflectance study in the E0 and E00 transition regions of GaP

    Page(s): 4904 - 4909
    Save to Project icon | PDF file iconPDF (99 KB)  

    Photoreflectance (PR) measurements have been carried out to determine the E0 and E00 critical-point (CP) parameters in GaP at temperatures between 12 and 300 K using a He–Cd laser as modulation light source. The measured PR spectra provide distinct structures at ∼2.75–2.85 eV (E0) and ∼2.85–2.95 eV (E00). These structures are successfully explained by a three-dimensional (3D) one-electron line shape plus an excitonic shape. The temperature dependence of the 3D CP and excitonic parameters (energy, amplitude, and broadening parameter) have been determined and analyzed using the Varshni equation and an empirical expression of Bose–Einstein type. The rapid decrease in the PR signal amplitudes is observed at T≪100 K and can be explained by the weakened surface electric fields due to carrier freezing at such low temperatures. The 3D exciton binding energy at the E0/(E00) edges of GaP has also been determined to be 13 meV. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical parameters of a magnetized space-charge neutral group IV semiconductor

    Page(s): 4910 - 4916
    Save to Project icon | PDF file iconPDF (106 KB)  

    Using a hydrodynamic model of semiconductor plasmas, we report an analytical investigation of hot-carrier induced nonlinearity and its impact on the optical parameters (refractive index and absorption coefficient) of a magnetized, space-charge neutral group IV semiconductor. The carrier heating by the pump is assumed to induce nonlinearity in the medium through momentum transfer collision frequency ν of the carriers and space-charge neutrality of the medium. For the linear optical parameters (nl, al), both electrons and holes are found to contribute resonantly at high frequency of the pump 0≈ωce). For the nonlinear optical parameters (n2, a2), the holes contribute significantly in the low pump frequency regime 0≈ωch,) whereas in the high pump frequency regime 0≈ωce), both kinds of carriers contribute resonantly in which a much larger contribution comes from the electrons. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Outgoing multiphonon resonant Raman scattering and luminescence in Be- and C-implanted GaN

    Page(s): 4917 - 4921
    Save to Project icon | PDF file iconPDF (157 KB)  

    We have performed outgoing resonant Raman scattering and photoluminescence measurements on as-grown, Be- and C-implanted GaN in the temperature range of 77–330 K. In implanted GaN after postimplantation annealing at 1100 °C, the A1(LO) multiphonons up to the seventh order were observed with the very strong four longitudinal optical (LO) and five LO modes at ∼2955 and ∼3690 cm-1, respectively, showing extraordinary resonance behavior. With the sample temperature, these two modes significantly decreased and increased in intensity, respectively. The phenomenon is attributed to the variation of resonant conditions due to the shift of the band gap energy. Meanwhile, the combination of E2(high) and quasi-LO phonons was strongly enhanced by quasi-LO phonon involvement and thus the corresponding overtones can be clearly observed even up to the sixth order (m=6). The mechanisms that such strong outgoing multiphonon resonance Raman scattering occurred to implanted GaN instead of high-quality as-grown GaN samples can be attributed to the strong Frohlich-induced scattering by LO phonons and exciton-mediated resonant Raman scattering with impurity inducement. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electronic linear energy transfer dependent molecular structural growth in polyethylene terephthalate

    Page(s): 4922 - 4927
    Save to Project icon | PDF file iconPDF (96 KB)  

    Thin films (13 μm) of polyethelene terephthalate (PET) are irradiated by different swift metallic heavy ions (180 MeV Ag14+ and 200 MeV Au15+) with the projectile linear energy transfer (LET) (∼10–14 keV/nm), respectively. LET dependence on the molecular structural changes in PFT irradiated at different ion fluences has been studied by the Fourier transform infrared spectroscopy. The study has revealed that beyond a critical LET entirely different pathways of amorphization beginning with partial recrystallization at lower ion fluence impact occurs in PET, contrary to the earlier established results. At considerably higher LET (∼14 keV/nm), the most characteristic crystalline stretching and bending vibration bands such as at 850 cm-1 (CH2 rocking), 972 cm-1 (CO stretching), 1341 and 1471 cm-1 (CH2 bending) in PET have shown a significant rise in the respective infrared absorbance intensities upon lower ion fluence (∼1011 ions/cm2) impact. The absence of previously reported unsaturations such as alkynes at both the LET beam used are also observed. Interestingly, the aromatic system also appears to be unstable and participating in the modification process, particularly at the higher LET (∼14 KeV/nm). Possible interpretations are discussed. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • GaCl molecular dynamics on a GaAs surface during GaAs epitaxial growth

    Page(s): 4928 - 4931
    Save to Project icon | PDF file iconPDF (265 KB)  

    To verify that a high quality layer was grown on a GaAs(001) substrate but not on a GaAs(110) substrate, we studied the dynamical behaviors of GaCl molecules on GaAs(001) 2×4 and GaAs(110) 1×1 surfaces. Trapped GaCl desorbed rapidly from the GaAs(110) 1×1 surface compared to the GaAs(001) 2×4 surface. We estimated the activation energy corresponding to GaCl trapping wells to be 92 kJ/mol on the GaAs(001) 2×4 surface and 54 kJ/mol on the GaAs(110) 1×1 surface. These results suggest that the interaction between GaCl molecules and GaAs surfaces deeply influences the quality of layers grown on GaAs substrates. © 2002 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

Full Aims & Scope

Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory