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15 Jul 2005

Volume 98, Issue 2, Articles (02xxxx)

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Fluorine-doping concentration and fictive temperature dependence of self-trapped holes in SiO2 glasses

R. P. Wang, N. Tai, K. Saito, and A. J. Ikushima

J. Appl. Phys. 98, 023701 (2005); http://dx.doi.org/10.1063/1.1980536 (3 pages)

Online Publication Date: 18 July 2005

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Fictive temperature (Tf) and fluorine (F)-doping concentration dependences of self-trapped holes (STHs) in silica glasses created by UV irradiation at low temperatures have been studied by the electron-paramagnetic-resonance method. It was found that the yield of STH decreases with decreasing Tf and increasing F-doping concentration. In combination with infrared spectra measurements, the correlation among Tf, F-doping concentration, Si–O bond length, and Si–O–Si bond angle was elucidated. We conclude that the change in both Tf and F doping can modify the network of SiO2 glass, leading to the suppression of the formation of STHs.
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61.72.S- Impurities in crystals
71.55.Ht Other nonmetals
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
76.30.-v Electron paramagnetic resonance and relaxation

Effect of thermal annealing on the interband transitions and activation energies of CdTe/ZnTe quantum dots

H. S. Lee, K. H. Lee, H. L. Park, T. W. Kim, and Y.-H. Kim

J. Appl. Phys. 98, 023702 (2005); http://dx.doi.org/10.1063/1.1968440 (4 pages) | Cited 1 time

Online Publication Date: 19 July 2005

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The effect of rapid thermal annealing on CdTe/ZnTe quantum dots (QDs) was analyzed to investigate the interband transitions and the electron activation energy. The full width at half maximum of the photoluminescence (PL) peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band (E1‐HH1) in the CdTe/ZnTe QDs annealed at 330 °C decreased, and their integrated PL intensity of the E1‐HH1 transition peak significantly increased. The activation energy of electrons confined in CdTe/ZnTe QDs annealed at 330 °C increased as high as 77 meV, which was the highest value among the as-grown and annealed samples. These results indicate that the crystallinity of the CdTe/ZnTe QDs is improved by annealing, and the present results can help improve the understanding of the thermal annealing effect on the optical properties of CdTe/ZnTe QDs.
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61.72.Cc Kinetics of defect formation and annealing
73.21.La Quantum dots
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots

Thermally activated carrier transfer processes in InGaN/GaN multi-quantum-well light-emitting devices

C. L. Yang, L. Ding, J. N. Wang, K. K. Fung, W. K. Ge, H. Liang, L. S. Yu, Y. D. Qi, D. L. Wang, Z. D. Lu, and K. M. Lau

J. Appl. Phys. 98, 023703 (2005); http://dx.doi.org/10.1063/1.1978967 (5 pages) | Cited 7 times

Online Publication Date: 19 July 2005

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We have studied the temperature-dependent carrier transfer processes in InGaN/GaN multi-quantum-well light-emitting devices using various optical techniques such as photoluminescence, electroluminescence, and photoluminescence excitation spectra. The role of the defects in the GaN barrier neighboring to the InGaN region was demonstrated clearly in capturing carriers only at low temperatures. The physical origin of the defects was most possibly attributed to the stacking faults at the interface according to the high-resolution transmission electron spectroscopy pictures.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Charge trap levels in sulfur-doped chemical-vapor-deposited diamond with applications to ultraviolet dosimetry

E. Trajkov, S. Prawer, J. E. Butler, and S. M. Hearne

J. Appl. Phys. 98, 023704 (2005); http://dx.doi.org/10.1063/1.1984079 (7 pages) | Cited 4 times

Online Publication Date: 19 July 2005

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Electrically active defects and traps in sulfur-doped polycrystalline diamond films synthesized by microwave-assisted chemical-vapor deposition are evaluated using thermally stimulated conductivity measurements after ultraviolet (UV) illumination. The measurements are found to be consistent with the latest theoretical predictions for the role of sulfur dopants in diamond. The suitability of S-doped diamond as a UV dosimeter is discussed.
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81.05.Cy Elemental semiconductors
71.55.Cn Elemental semiconductors
71.20.Mq Elemental semiconductors
73.61.Cw Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Electronic structure of silicon quantum dots: Calculations of energy-gap redshifts due to oxidation

Masahiko Nishida

J. Appl. Phys. 98, 023705 (2005); http://dx.doi.org/10.1063/1.1985978 (6 pages) | Cited 9 times

Online Publication Date: 20 July 2005

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Electronic state calculations are performed self-consistently using the extended Hückel-type nonorthogonal tight-binding method for two different oxygen configurations (backbonded and double-bonded oxygen configurations) on the H-covered surface of spherical Si35H36, Si47H60, Si71H84, Si136H120, Si148H120, and Si172H120 quantum dots. The size dependence of the effect of oxygen on the electronic structure of the Si dots is studied. Energy gaps calculated for both oxygen configurations can explain oxidation-induced redshifts in photoluminescence (PL) observed in porous Si. However, the energy gaps calculated for the backbonded oxygen model are around 2.2 eV and dipole allowed in all Si dots studied, whereas those for the double-bonded oxygen model are gradually decreased with the increase in size (2.3–1.7 eV), and optical transitions are dipole forbidden in the Si dots near 1 nm across and dipole allowed in the ones near 2 nm in diameter. The results calculated for the backbonded oxygen model coincide well with the experimental fact that the PL-peak energies are fixed at ∼ 2.1 eV when porous Si is exposed to air.
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71.20.Mq Elemental semiconductors
78.55.Ap Elemental semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Electrical transport properties of aluminum-implanted 4H–SiC

J. Pernot, S. Contreras, and J. Camassel

J. Appl. Phys. 98, 023706 (2005); http://dx.doi.org/10.1063/1.1978987 (9 pages) | Cited 14 times

Online Publication Date: 20 July 2005

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The free hole density and low-field mobility of aluminum-doped 4H–SiC were investigated in the temperature range of 100–900 K, both, experimentally and theoretically. Experimental data for implanted p-type 4H–SiC were compared with theoretical calculations using parameters determined for high-quality epitaxial layers. The deformation potential for intra- and intervalley scattering by acoustic phonons and the effective coupling constant for intra- and intervalley scattering by nonpolar optical phonons were determined. The detailed analysis of the implanted layers with aluminum-targeted concentration ranging from 3.33×1018 to 1021 cm−3 shows that (i) about half of the implanted atoms are electrically active in the SiC lattice, (ii) a systematic compensation of about 10% of the doping level is induced by the implantation process, (iii) two different ionization energies for the aluminum atoms have to be used. Their origin is discussed in terms of inequivalent hexagonal and cubic lattice sites. Finally, the doping dependence of the ionization ratio and Hall mobility are given for non- and weakly (10%) compensated material at 292 K. The maximum achievable mobility for low-doped material in p-type 4H–SiC is shown to be 93 cm2/V s at room temperature.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.72.up Other materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
72.20.My Galvanomagnetic and other magnetotransport effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.80.Jc Other crystalline inorganic semiconductors

Molecular and solid-state (8-hydroxy-quinoline)aluminum interaction with magnesium: A first-principles study

S. Meloni, A. Palma, A. Kahn, J. Schwartz, and R. Car

J. Appl. Phys. 98, 023707 (2005); http://dx.doi.org/10.1063/1.1953869 (8 pages)

Online Publication Date: 21 July 2005

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The interaction between Mg and (8-hydroxyquinoline)aluminum, Alq3, is investigated via ab initio molecular dynamics based on density-functional theory. We model the Alq3 thin film both with a single Alq3 molecule in vacuo (as is usually done in the literature) and with an Alq3 crystalline structure. Comparing the results from these two models, we show that bulk calculations provide a better description of the chemical processes involved, allowing the Mg atom to react with two neighboring Alq3 molecules, as was alluded to in a previous publication [ S. Meloni, A. Palma, A. Kahn, J. Schwartz, and R. Car, J. Am. Chem. Soc. 125, 7808 (2003) ]. Moreover, core-level shift calculations are in good agreement with experimental measurements only when using the solid phase approach. We also propose a different interpretation of the Al(2p) experimental core level presented in a previous work [ C. Shen, A. Kahn, and J. Schwartz, J. Appl. Phys. 89, 449 (2001) ].
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
61.66.Hq Organic compounds

Irradiation effects on the compensation of semi-insulating GaAs for particle detector applications

Anna Cavallini and Laura Polenta

J. Appl. Phys. 98, 023708 (2005); http://dx.doi.org/10.1063/1.1978989 (5 pages) | Cited 3 times

Online Publication Date: 21 July 2005

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The distribution of the electric field and its spatial extent are key predictors of the charge collection efficiency of particle detectors. The electric field is strictly related to the electrically active defects, which are significantly modified by irradiation. In this paper we analyze the native and radiation-induced defects and infer the mechanisms controlling the electrical properties of semi-insulating GaAs Schottky diodes. The correlation between the electric-field distribution and deep levels confirms that the compensation mechanisms are mainly due to the donorlike centers and to their enhanced neutralization, which occurs for moderately high electric fields. Moreover, taking into account the charge balance among native and irradiation-induced defects, the active region extent is predicted.
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61.82.Fk Semiconductors
61.80.Hg Neutron radiation effects
61.80.Jh Ion radiation effects
71.55.Eq III-V semiconductors
85.30.Kk Junction diodes
73.61.Ey III-V semiconductors

Formation of two-dimensional electron gases in polytypic SiC heterostructures

V. M. Polyakov and F. Schwierz

J. Appl. Phys. 98, 023709 (2005); http://dx.doi.org/10.1063/1.1984070 (6 pages) | Cited 17 times

Online Publication Date: 25 July 2005

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The formation of two-dimensional electron gases (2DEGs) at polytypic (hexagonal/cubic) SiC heterojunctions (4H/3C SiC and 6H/3C SiC) is investigated by numerical self-consistent solutions of the Schrödinger and Poisson equations. The free-electron-density distributions and conduction-band profiles in the SiC heterostructures are calculated and compared to those occurring at AlGaN/GaN interfaces. Spontaneous and piezoelectric polarization effects in both SiC/SiC and AlGaN/GaN structures are taken into account. The combined effect of the polarization-induced bound charge and conduction-band offset between the hexagonal and cubic SiC polytypes results in the formation of 2DEGs with very high electron sheet concentration. 2DEG sheet densities about 20% larger than that in Al0.3Ga0.7N/GaN structures are calculated for 4H/3C SiC heterostructures. We also find that the 2DEG densities in the 4H/3C are much less sensitive to variations of the barrier layer thickness. The influence of the barrier doping layer on the 2DEG densities is also investigated.
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81.05.Hd Other semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
77.22.Ej Polarization and depolarization
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.63.-b Electronic transport in nanoscale materials and structures
72.20.-i Conductivity phenomena in semiconductors and insulators
61.72.up Other materials

Study of structural-, compositional-, and thickness-dependent thermoelectric and electrical properties of Bi93Sb7 alloy thin films

Ramesh Chandra Mallik and V. Damodara Das

J. Appl. Phys. 98, 023710 (2005); http://dx.doi.org/10.1063/1.1957126 (8 pages) | Cited 2 times

Online Publication Date: 26 July 2005

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We have used the melt-quenching technique to prepare the bulk material and vapor-quenching technique to prepare the thin films of Bi93Sb7 alloy. The Bi93Sb7 alloy thin films of different thicknesses were grown onto well-cleaned glass and silicon substrates. The films were annealed at 150 ° C for 4 h in a vacuum of the order of 10−6 torr in order to remove the defects and to increase the grain size. The bulk and thin-film x-ray diffraction results agree with the transmission electron microscopy results and the compositional analysis of bulk by particle-induced x-ray emission and of thin films by Rutherford backscattering. The thickness and temperature dependences of thermoelectric power and electrical resistivity have been analyzed. The negative temperature coefficient of resistivity confirmed that the material is semiconducting in nature. The negative thermoelectric power confirmed that the present bismuth-rich material is a n type. In this paper we have made an attempt to study the thermoelectric properties of bulk as well as thin films of Bi93Sb7, maintaining the same composition. The scattering index parameter was calculated from the experimental data and was compared with the theoretical predictions of the size effect theory.
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72.15.Jf Thermoelectric and thermomagnetic effects
73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
61.72.Cc Kinetics of defect formation and annealing
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
68.37.Lp Transmission electron microscopy (TEM)

Effects of nitrogen, oxygen, and moisture on the electron transport in tris(8-hydroxyquinoline) aluminum

H. H. Fong and S. K. So

J. Appl. Phys. 98, 023711 (2005); http://dx.doi.org/10.1063/1.1990258 (4 pages) | Cited 13 times

Online Publication Date: 26 July 2005

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The effects of nitrogen, oxygen, and moisture on the electron mobilities of tris(8-hydroxyquinoline) aluminum (Alq3) have been examined by time-of-flight (TOF) technique at room temperature under an applied electric-field range of 0.3–1 MV/cm. Our results suggest that both oxygen and water molecules can impede electron conduction in Alq3. Detailed analysis suggests that water molecules induce electron traps even at very low dosages. Oxygen interacts with Alq3 at high dosages and results in highly dispersive TOF signals. Moisture appears to be more detrimental than oxygen in hindering electron transport in Alq3.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ee Mobility edges; hopping transport

Effects of strain relaxation on the electronic properties of epitaxial Sr2FeMoO6 grown by pulsed laser deposition on SrTiO3 (001)

T. Fix, D. Stoeffler, S. Colis, C. Ulhaq, G. Versini, J. P. Vola, F. Huber, and A. Dinia

J. Appl. Phys. 98, 023712 (2005); http://dx.doi.org/10.1063/1.1925761 (4 pages) | Cited 11 times

Online Publication Date: 26 July 2005

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Thin films of Sr2FeMoO6 (SFMO) are grown epitaxially on (001) SrTiO3 substrates by pulsed laser deposition. The in-plane and out-of-plane SFMO lattice parameters are determined for different thicknesses, from 13 to 600 nm. Samples below a critical thickness of around 34 nm are fully strained, samples between 34 and 80 nm are relaxing, and samples between 80 and 600 nm are fully relaxed. Transmission electron microscopy reveals that the relaxation is done by stacking the faults perpendicular to the substrate. Ab initio calculations show first that the variation of SFMO lattice parameters due to strain has a limited impact on the magnetization, which is also observed experimentally. Second, ab initio calculations indicate that SFMO is half metallic only for thicknesses above 44 nm.
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68.60.Bs Mechanical and acoustical properties
73.61.-r Electrical properties of specific thin films
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.-x Mechanical properties of solids
61.72.Nn Stacking faults and other planar or extended defects

Effects of annealing temperature on the degree of inhomogeneity of nickel-silicide/SiC Schottky barrier

L. Calcagno, A. Ruggiero, F. Roccaforte, and F. La Via

J. Appl. Phys. 98, 023713 (2005); http://dx.doi.org/10.1063/1.1978969 (6 pages) | Cited 7 times

Online Publication Date: 26 July 2005

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The electrical characteristics of nickel-silicide Schottky contacts on silicon carbide have been measured by using current-voltage technique in the temperature range of 120–700 K. Thermal annealing at 873 K formed the nickel silicide. The electrical behavior of the contact showed a deviation from linearity at low temperatures. Annealing at high temperature (1223 K) produces deep modifications in the electrical characteristics at low bias and low temperatures, which are consistent with the formation of an inhomogeneous barrier. The description of the experimental results by using Tung’s model [ R. T. Tung, Phys. Rev. B 45, 13509 (1992) ] allowed us to determine the values of the average barrier height of 1.62 and 1.14 eV for the diode annealed at 873 and 1223 K, respectively.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
73.40.Ei Rectification
61.72.Cc Kinetics of defect formation and annealing

Positive and negative temperature dependences of electron-impact ionization in In0.53Ga0.47As

K. Y. Choo and D. S. Ong

J. Appl. Phys. 98, 023714 (2005); http://dx.doi.org/10.1063/1.1993755 (4 pages) | Cited 1 time

Online Publication Date: 26 July 2005

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The electron-impact ionization coefficient (α) in In0.53Ga0.47As increases with temperature at electric fields below 200 kV/cm, in contrast to most crystalline semiconductors. It exhibits conventional negative temperature dependence at higher fields. A four-valley analytical band Monte Carlo model is used to study this anomalous behavior. The simulations show that both alloy scattering and the temperature dependence of the impact ionization threshold energy contribute to the temperature dependence of α. At low fields, we find that most ionization events occur in the first conduction band causing an increase of α with temperature in In0.53Ga0.47As. At high fields, α decreases with temperature again because of the reduced hot-electron population in the second conduction band.
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72.20.Ht High-field and nonlinear effects
72.80.Ey III-V and II-VI semiconductors

Structural, electrical, optical, and mechanical characterizations of decorative ZrOxNy thin films

P. Carvalho, F. Vaz, L. Rebouta, L. Cunha, C. J. Tavares, C. Moura, E. Alves, A. Cavaleiro, Ph. Goudeau, E. Le Bourhis, J. P. Rivière, J. F. Pierson, and O. Banakh

J. Appl. Phys. 98, 023715 (2005); http://dx.doi.org/10.1063/1.1990261 (8 pages) | Cited 31 times

Online Publication Date: 28 July 2005

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The main objective of this work is the preparation of decorative zirconium oxynitride, ZrOxNy, thin films by dc reactive magnetron sputtering. Film properties were analyzed as a function of the reactive gas flow and were correlated with the observed structural changes. Measurements showed a systematic decrease in the deposition rate with the increase of the reactive gas flow and revealed three distinct modes: (i) a metallic mode, (ii) a transition mode (subdivided into three zones), and (iii) an oxide mode. The measurements of target potential were also consistent with these changes, revealing a systematic increase from 314 to 337 V. Structural characterization uncovered different behaviors within each of the different zones, with a strong dependence of film texture on the oxygen content. These structural changes were also confirmed by resistivity measurements, whose values ranged from 250 to 400 μΩ cm for low gas flows and up to 106 μΩ cm for the highest flow rates. Color measurements in the films revealed a change from bright yellow at low reactive gas flows to red brownish at intermediate flows and dark blue for the films prepared at the highest flows. Hardness measurements gave higher values for the region where larger grain sizes were found, showing that the grain growth hardening effect is one of the main parameters that can help explain the observed behavior. Also the peak intensity ratio and the residual stress states were found to be important factors for explaining this behavior.
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68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
73.61.Ng Insulators
78.66.Nk Insulators
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Time-resolved spin filtering in semiconductor symmetric resonant barrier structures

Leo Yu and O. Voskoboynikov

J. Appl. Phys. 98, 023716 (2005); http://dx.doi.org/10.1063/1.1994945 (5 pages) | Cited 7 times

Online Publication Date: 29 July 2005

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Spin-dependent tunneling in semiconductor symmetric double barrier structures is studied theoretically. Our calculation is based on the effective one-band Hamiltonian and Dresselhaus spin-orbit coupling. We demonstrate that the ratio of the tunneling times of electrons with opposite spin orientations can vary over a few orders in magnitude. The large and tunable ratio of the tunneling times can serve as the basis in the development of all-semiconductor dynamic spin filters.
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72.25.Dc Spin polarized transport in semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.23.-b Electronic transport in mesoscopic systems
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