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10 Jul 2006

Volume 89, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 023901 (2006); http://dx.doi.org/10.1063/1.2219984 (3 pages)

Nikhil Ganesh, Ian D. Block, and Brian T. Cunningham
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Visualization of the complex refractive index of a conductor by frustrated total internal reflection

Yu. P. Bliokh, R. Vander, S. G. Lipson, and J. Felsteiner

Appl. Phys. Lett. 89, 021908 (2006); http://dx.doi.org/10.1063/1.2220540 (3 pages) | Cited 3 times

Online Publication Date: 11 July 2006

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A simple imaging geometry in which total internal reflection in a glass prism is frustrated by the proximity of a metal surface is implemented for observation of surface plasmon resonance. At a certain angle of incidence, the total internal reflection is completely suppressed at a certain distance between the metal and the prism surfaces. Using planar metal and spherical prism surfaces, the distance parameter is sampled in a single image. This allows a direct determination of the complex refractive index in bulk samples as well as in thin films. Our experimental data are in good agreement with previously published data.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Bh Lenses, prisms and mirrors

Near-infrared scintillation of xenon by math beta decay

Norimasa Yoshimizu, Amit Lal, and Clifford R. Pollock

Appl. Phys. Lett. 89, 021909 (2006); http://dx.doi.org/10.1063/1.2218063 (3 pages)

Online Publication Date: 11 July 2006

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The near-infrared scintillation of xenon gas by the β decay of 37 MBq of math was studied, in the interest of its use in integrated devices for applications such as optical beacons and wavelength calibration. The emission was imaged and analyzed using Spencer’s theory of electron penetration using xenon scattering cross sections derived from Thomas-Fermi theory. The total emission was approximately 2×105 photons/s at 20 kPa and 1×105 photons/s at 100 kPa. Spectral data show three dominant peaks at 823, 828, and 882 nm as well as the formation of metastable states.
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51.70.+f Optical and dielectric properties
06.20.fb Standards and calibration

Controlled blueshift of the resonant wavelength in porous silicon microcavities using ion irradiation

D. Mangaiyarkarasi, M. B. H. Breese, Y. S. Ow, and C. Vijila

Appl. Phys. Lett. 89, 021910 (2006); http://dx.doi.org/10.1063/1.2219989 (3 pages) | Cited 7 times

Online Publication Date: 12 July 2006

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High-energy focused proton beam irradiation has been used to controllably blueshift the resonant wavelength of porous silicon microcavities in heavily doped p-type wafers. Irradiation results in an increased resistivity, hence a locally reduced rate of anodization. Irradiated regions are consequently thinner and of a higher refractive index than unirradiated regions, and the microcavity blueshift arises from a net reduction in the optical thickness of each porous layer. Using this process wafers are patterned on a micrometer lateral scale with microcavities tuned to different resonant wavelengths, giving rise to high-resolution full-color reflection images over the full visible spectrum.
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61.82.Fk Semiconductors
61.80.Jh Ion radiation effects
81.65.Cf Surface cleaning, etching, patterning
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
82.45.-h Electrochemistry and electrophoresis

Mapping substrate/film adhesion with contact-resonance-frequency atomic force microscopy

D. C. Hurley, M. Kopycinska-Müller, E. D. Langlois, A. B. Kos, and N. Barbosa

Appl. Phys. Lett. 89, 021911 (2006); http://dx.doi.org/10.1063/1.2221404 (3 pages) | Cited 9 times

Online Publication Date: 12 July 2006

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We have used contact-resonance-frequency atomic force microscopy techniques to nondestructively image variations in adhesion at a buried interface. Images were acquired on a sample containing a 20 nm gold (Au) blanket film on silicon (Si) with a 1 nm patterned interlayer of titanium (Ti). This design produced regions of very weak adhesion (Si/Au) and regions of strong adhesion (Si/Ti/Au). Values of the contact stiffness were 5% lower in the regions of weak adhesion. The observed behavior is consistent with theoretical predictions for layered systems with disbonds. Our results represent progress towards quantitative measurement of adhesion parameters on the nanoscale.
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68.35.Ct Interface structure and roughness
68.37.Ps Atomic force microscopy (AFM)
68.35.Np Adhesion
68.35.Gy Mechanical properties; surface strains
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Anomalous temperature dependence of absorption edge in narrow-gap HgCdTe semiconductors

Fangyu Yue, Jun Shao, Xiang Lü, Wei Huang, Junhao Chu, Jun Wu, Xingchao Lin, and Li He

Appl. Phys. Lett. 89, 021912 (2006); http://dx.doi.org/10.1063/1.2221411 (3 pages) | Cited 16 times

Online Publication Date: 12 July 2006

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Abnormal temperature dependence of absorption edge is reported for narrow-gap Hg1−xCdxTe semiconductors at low temperature. Infrared absorption spectra are taken for bulk and molecular-beam epitaxial Hg1−xCdxTe, respectively, in the temperature range of 11–300 K. The results indicate an abnormal shift of the absorption edge around the temperature range of 30–70 K. Analysis suggests that (i) the phenomenon is introduced by Hg vacancies in the samples, of which the energy level locates about 9–12 meV above the Hg1−xCdxTe valence band, and (ii) the conventional criterion for the determination of band gap energy, Eg, from absorption spectra is not accurate enough as soon as Hg vacancies exist, especially at a temperature above 77 K. It hence provides an explanation why there should exist difference between the cutoff wavelength of the detector and the absorption-edge (Eg) wavelength of the material the detector was made of.
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78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
61.72.J- Point defects and defect clusters

Stabilized switchable “black state” in Mg2NiH4/Ti/Pd thin films for optical hydrogen sensing

M. Pasturel, M. Slaman, D. M. Borsa, H. Schreuders, B. Dam, R. Griessen, W. Lohstroh, and A. Borgschulte

Appl. Phys. Lett. 89, 021913 (2006); http://dx.doi.org/10.1063/1.2221412 (3 pages) | Cited 11 times

Online Publication Date: 12 July 2006

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A triple layer thin film (30 nm Mg2Ni/100 nm Ti/10 nm Pd sputtered on glass) switches reversibly from a shiny metallic to a “black” state upon exposure to moderate hydrogen pressure ( ≈ 5.103 Pa). This black state resembles that obtained in thick Mg2NiHx layers and has the great advantage of being stable and easily controlled. Both the reversible high optical contrast (Rreflective/Rblack ≈ 10 in the red wavelength range) and the fast kinetics of hydrogen absorption and desorption make this material interesting for applications as optical hydrogen sensors.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.43.Mn Adsorption kinetics
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Phase change observation in reflection multilayers by total electron yield and reflection spectra

Takeo Ejima, Tetsuo Harada, and Atsushi Yamazaki

Appl. Phys. Lett. 89, 021914 (2006); http://dx.doi.org/10.1063/1.2220061 (3 pages) | Cited 2 times

Online Publication Date: 13 July 2006

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Precise optical elements for use in the extreme ultraviolet region are necessary for controlling both the uppermost layer thickness and the reflection phase in a reflection multilayer system. In this study, a phase value corresponding to both the uppermost layer thickness and the reflection phase was derived from the reflectance and total electron yield (TEY) intensity. Mo/Si multilayers were fabricated on a silicon wafer with various thicknesses of the uppermost Mo layer. Phase values obtained from the reflection and TEY measurements were found to change in accordance with increases in the thickness of the uppermost Mo layer and a concomitant change in the reflection phase.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.-a Optical materials
42.79.Wc Optical coatings
78.40.Fy Semiconductors
78.40.Kc Metals, semimetals, and alloys

Intense photoluminescence from amorphous tantalum oxide films

Minmin Zhu, Zhengjun Zhang, and Wei Miao

Appl. Phys. Lett. 89, 021915 (2006); http://dx.doi.org/10.1063/1.2219991 (3 pages) | Cited 21 times

Online Publication Date: 13 July 2006

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Tantalum oxide films were deposited on silicon substrates at a temperature of ∼ 450 °C by heating a pure tantalum foil in a rough vacuum. The films were amorphous in structure and consisted of fully oxidized Ta2O5 and (TaOx, x<2.5) suboxides. This feature resulted in strong visible light emission from the films further oxidized in the air at temperatures of 200–300 °C. The mechanism for this photoluminescence behavior of the amorphous tantalum oxide films was also investigated and discussed. This study suggests that wide-band-gap materials could act as effective visible light emitters and provides a simple route to synthesize such materials.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments
68.55.-a Thin film structure and morphology

Impact of 4H– and 6H–SiC(0001) nitridation on Ga wetting layer development and GaN growth by molecular beam epitaxy

Tong-Ho Kim, Soojeong Choi, April S. Brown, Maria Losurdo, and Giovanni Bruno

Appl. Phys. Lett. 89, 021916 (2006); http://dx.doi.org/10.1063/1.2220007 (3 pages) | Cited 3 times

Online Publication Date: 13 July 2006

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GaN epitaxial layers have been grown by plasma-assisted molecular beam epitaxy on Si-face 4H– and 6H–SiC(0001)Si substrates. The impact of the SiC surface preparation and oxide removal achieved via a Ga flash-off process followed by nitridation on the structure and properties of GaN epitaxial layers is articulated. A correlation among the SiC surface nitridation conditions, the Ga wetting layer development, the nucleation layer, and GaN crystalline properties is revealed.
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81.05.Ea III-V semiconductors
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.-j Plasma applications
68.55.A- Nucleation and growth

First-principles prediction of low shear-strain resistance of Al3BC3: A metal borocarbide containing short linear BC2 units

Jingyang Wang, Yanchun Zhou, Ting Liao, and Zhijun Lin

Appl. Phys. Lett. 89, 021917 (2006); http://dx.doi.org/10.1063/1.2220549 (3 pages) | Cited 30 times

Online Publication Date: 13 July 2006

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The elastic stiffness and shear deformation mode of Al3BC3, a metal borocarbide containing linear C–B–C units, are studied based on the first-principles total energy calculations. The predominant effect of C–B–C units on mechanical properties is reported by leading to low shear modulus. The low shear-strain resistance originates from the deformation mode as follows: the rigid linear C–B–C units tilt with respect to the c direction easily, and the corner-sharing Al5C bipyramid slabs simultaneously slide along the basal plane with low resistance. The proposed deformation mode may be universal for the ternary metal borocarbides family containing short linear C–B–C units.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
71.15.Nc Total energy and cohesive energy calculations

Strongly enhanced nitriding kinetics by means of grain refinement

W. P. Tong, C. S. He, J. C. He, L. Zuo, N. R. Tao, and Z. B. Wang

Appl. Phys. Lett. 89, 021918 (2006); http://dx.doi.org/10.1063/1.2221498 (3 pages) | Cited 8 times

Online Publication Date: 13 July 2006

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By means of surface mechanical attrition treatment (SMAT), a nanostructured surface layer was formed on a pure Fe plate. Low-temperature gaseous nitriding of the SMAT Fe sample was investigated in comparison with the coarse-grained sample. It was found that the nitriding kinetics of nanostructured α-Fe was obviously enhanced, and the temperature to form nitrides from the nanostructured α-Fe was greatly reduced with respect to that of the coarse-grained form. The effective activation energy for diffusion of nitrogen in nanocrystalline nitride layer was calculated from the temperature dependence of compound layer thickness, the obtained value being about 54.39 kJ/mol, evidently smaller than that for coarse-grained ε phase (80.7 kJ/mol) and γ′ phase (88.3 kJ/mol).
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81.07.Bc Nanocrystalline materials
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
66.30.J- Diffusion of impurities
61.46.Hk Nanocrystals

Coarse-grained model for a molecular crystal

Richard H. Gee, Christine Wu, and Amitesh Maiti

Appl. Phys. Lett. 89, 021919 (2006); http://dx.doi.org/10.1063/1.2221878 (3 pages) | Cited 5 times

Online Publication Date: 14 July 2006

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Using the energetic material pentaerythritol tetranitrate as a specific example of molecular crystal, we describe the development of a simple coarse-graining procedure by grouping several atoms or whole functional groups into single charge-neutral beads. As compared to fully atomistic calculations the coarse-grained model speeds up simulations by more than two orders of magnitude. Yet, by adjusting only two parameters in the coarse-grained interaction, the model accurately predicts the lattice constants, sublimation energy, pressure-volume curve up to P = 10 GPa, and energetically the most stable facets. Computed surface and desorption energies, bulk modulus, and equilibrium morphology are reported as well.
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61.66.Hq Organic compounds
68.35.Md Surface thermodynamics, surface energies
68.43.Mn Adsorption kinetics
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Experimental studies on intermediate compound of LiBH4

Shin-Ichi Orimo, Yuko Nakamori, Nobuko Ohba, Kazutoshi Miwa, Masakazu Aoki, Shin-ichi Towata, and Andreas Züttel

Appl. Phys. Lett. 89, 021920 (2006); http://dx.doi.org/10.1063/1.2221880 (3 pages) | Cited 79 times

Online Publication Date: 14 July 2006

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The formation condition of an intermediate compound of LiBH4 during the partial dehydriding reaction and its local atomistic structure have been experimentally investigated. LiBH4 changes into an intermediate compound accompanying the release of approximately 11 mass % of hydrogen at 700–730 K. The Raman spectra indicate that the B–H bending and stretching modes of the compound appear at lower and higher frequencies, respectively, as compared to those of LiBH4. These features are consistent with the theoretical calculation on the monoclinic Li2B12H12, consisting of Li+ and [B12H12]2− ions, as a possible intermediate compound of LiBH4.
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78.30.Hv Other nonmetallic inorganics
61.66.Fn Inorganic compounds

Synthesis of bulk metallic glass foam by powder extrusion with a fugitive second phase

Min Ha Lee and Daniel J. Sordelet

Appl. Phys. Lett. 89, 021921 (2006); http://dx.doi.org/10.1063/1.2221882 (3 pages) | Cited 15 times

Online Publication Date: 14 July 2006

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Bulk metallic glass foams with 12 mm in diameter and 30 mm in length having a density of 4.62 g/cm3 (approximately 58.3% of theoretical) were fabricated by extruding a powder mixture comprised of 60 vol % Ni59Zr20Ti16Si2Sn3 metallic glass blended with 40 vol % brass followed by dissolution of the fugitive brass in an aqueous HNO3 solution. The final structure consists of continuously connected, high aspect ratio metallic glass struts surrounded by ∼ 40 vol % of homogeneously distributed ellipsoid-shaped pores having nominal diameters between 10 and 50 μm.
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81.05.Kf Glasses (including metallic glasses)
81.05.Bx Metals, semimetals, and alloys
81.05.Rm Porous materials; granular materials
82.70.Rr Aerosols and foams
61.43.Fs Glasses
61.43.Gt Powders, porous materials

X-ray diffraction peaks at glancing incidence and glancing exit from highly mismatched epitaxial layers

V. M. Kaganer, A. Shalimov, J. Bak-Misiuk, and K. H. Ploog

Appl. Phys. Lett. 89, 021922 (2006); http://dx.doi.org/10.1063/1.2221885 (3 pages) | Cited 5 times

Online Publication Date: 14 July 2006

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We find that the widths of double-crystal x-ray diffraction peaks in asymmetric reflections of relaxed GaAs/Si(001) heteroepitaxial layers in reciprocal diffraction geometries (glancing incidence and glancing exit) are notably different. This observation is in agreement with previous measurements on other heteroepitaxial systems but apparently contradicts the reciprocity principle of electrodynamics. We show that the apparent contradiction originates from the summation of the scattered waves that are collected by the detector in a double-crystal setup and resolve it by giving an appropriate description of the peak widths.
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61.05.cp X-ray diffraction
61.05.cf X-ray scattering (including small-angle scattering)
78.70.Ck X-ray scattering
68.60.Bs Mechanical and acoustical properties
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Analysis of the charge transport in π-conjugated materials using generalized Langevin equation

Seong Hyun Kim, Sang Chul Lim, Jung Hun Lee, Chan Hoi Ku, Jae Bon Koo, Yong Suk Yang, and Taehyoung Zyung

Appl. Phys. Lett. 89, 022101 (2006); http://dx.doi.org/10.1063/1.2219993 (3 pages)

Online Publication Date: 10 July 2006

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The complex dielectric constants of several π-conjugated materials are measured, and generalized Langevin equation is used to analyze the dielectric behavior in the frequency domain. From the results of a fitting of the experimental data, all of the dielectric behaviors are well interpreted by the generalized Langevin equation which strongly suggests that the mechanism of the charge carrier transport in π-conjugated organic and polymeric materials is diffusion at dc and low frequencies and an oscillatory motion at (or near) phonon frequencies, and in between, a mixed mode of these two mechanisms.
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73.61.Ph Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)
66.30.-h Diffusion in solids
63.50.-x Vibrational states in disordered systems

Circular dichroism in second harmonic generation from oxidized Si (001)

Xiaoqin Li, J. Willits, S. T. Cundiff, I. M. P. Aarts, A. A E. Stevens, and D. S. Dessau

Appl. Phys. Lett. 89, 022102 (2006); http://dx.doi.org/10.1063/1.2220014 (3 pages) | Cited 4 times

Online Publication Date: 10 July 2006

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Circular dichroism in second harmonic generation (SHG) is often related to molecules and materials with chiral structures. In this letter, we report circular dichroism in SHG from anisotropic achiral oxidized Si (001) at room temperature. The dichroism value depends on the azimuthal angles of the crystal axes. Due to the simple nonlinear susceptibility elements involved, we were able to attribute the dichroism in SHG to interference between particular terms of the bulk electric quadrupole and surface dipole contributions. The presence of a phase shift between the bulk and surface SHG is required to observe circular dichroism.
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78.20.Fm Birefringence
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ek Optical activity
42.65.An Optical susceptibility, hyperpolarizability

Nanoscale carrier transport in Ti/Al/Ni/Au Ohmic contacts on AlGaN epilayers grown on Si(111)

F. Roccaforte, F. Iucolano, F. Giannazzo, A. Alberti, and V. Raineri

Appl. Phys. Lett. 89, 022103 (2006); http://dx.doi.org/10.1063/1.2220486 (3 pages) | Cited 16 times

Online Publication Date: 10 July 2006

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In this letter, a correlation between nanostructure and current flow in Ti/Al/Ni/Au Ohmic contacts on AlGaN films grown on Si(111) is reported. A cross correlation between conductive-atomic force microscopy and structural analyses (x-ray diffraction, transmission electron microscopy) demonstrates that the structure and the electrical properties of the different phases formed inside the reacted layer upon annealing are crucial for the nanoscale current transport. The experimental measurement of the resistivity of the main phases formed upon annealing (AlNi, AlAu4, and Al2Au) indicated that the low resistivity Al2Au phase provides preferential conductive paths for the current flow through the contact.
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73.40.Ns Metal-nonmetal contacts
73.63.-b Electronic transport in nanoscale materials and structures
73.61.Ey III-V semiconductors
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
68.37.Ps Atomic force microscopy (AFM)

Low-temperature solid-phase crystallization of amorphous silicon thin films deposited by rf magnetron sputtering with substrate bias

Seung-Ik Jun, Philip D. Rack, Timothy E. McKnight, Anatoli V. Melechko, and Michael L. Simpson

Appl. Phys. Lett. 89, 022104 (2006); http://dx.doi.org/10.1063/1.2219136 (3 pages) | Cited 2 times

Online Publication Date: 10 July 2006

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The crystallization properties of amorphous silicon (a-Si) thin film deposited by rf magnetron sputter deposition with substrate bias have been thoroughly characterized. The crystallization kinetics for films deposited with substrate bias is enhanced relative to unbiased a-Si by films. The enhanced crystallization for substrate biased a-Si films are attributed to ion enhanced nucleation of crystallites during sputter deposition which subsequently grow during the postdeposition anneal. Conversely films sputter deposited without substrate bias have more intrinsic defects and residual oxygen which enhance nucleation and retard growth, respectively, and lead to a large number of small crystallites.
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64.70.K- Solid-solid transitions
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
64.60.Q- Nucleation
61.72.Cc Kinetics of defect formation and annealing

Thermal stability and band alignments for Ge3N4 dielectrics on Ge

S. J. Wang, J. W. Chai, J. S. Pan, and A. C. H. Huan

Appl. Phys. Lett. 89, 022105 (2006); http://dx.doi.org/10.1063/1.2220531 (3 pages) | Cited 28 times

Online Publication Date: 10 July 2006

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Ge3N4 dielectrics were prepared on Ge surface by in situ direct atomic source nitridation. The thermal stability and band alignments for Ge3N4/Ge interfaces have been studied by using high-resolution x-ray photoemission spectroscopy. The in situ thermal treatment shows that Ge3N4 film has higher temperature thermal stability up to 550 °C in vacuum. The conduction- and valence-band offsets at Ge3N4/Ge interface are quite asymmetrical with the values of 2.22 and 1.11 eV, respectively.
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77.55.-g Dielectric thin films
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Hysteresis phenomena in reverse biased InAsSbP/InAs heterostructure

Stéphane Rathgeb, Jean-Pierre Moeglin, Alain Boffy, Marcel Pasquinelli, and Olivier Palais

Appl. Phys. Lett. 89, 022106 (2006); http://dx.doi.org/10.1063/1.2220532 (3 pages)

Online Publication Date: 10 July 2006

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We present experimental and theoretical results on InAsSbP/InAs photodetectors for infrared detection. An unexpected hysteresis has been shown during the current-voltage I(V) investigations (300 K). Drastic changes in the hysteresis cycle are observed depending on the temperature of the heterostructure. Additionally, the time step of the measurements has an influence on the hysteresis form. The appearance of such hysteresis can be explained by a tunneling effect and by considering the temperature of the structure. Experimental I(V) characteristics are in good agreement with the tunnel current coupled to a thermal approach.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling

Origin of the red luminescence in Mg-doped GaN

S. Zeng, G. N. Aliev, D. Wolverson, J. J. Davies, S. J. Bingham, D. A. Abdulmalik, P. G. Coleman, T. Wang, and P. J. Parbrook

Appl. Phys. Lett. 89, 022107 (2006); http://dx.doi.org/10.1063/1.2220552 (3 pages) | Cited 9 times

Online Publication Date: 10 July 2006

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Optically detected magnetic resonance and positron annihilation spectroscopy experiments have been employed to study magnesium-doped GaN layers grown by metal-organic vapor phase epitaxy. As the Mg doping level is changed, the combined experiments reveal a strong correlation between the vacancy concentrations and the intensity of the red photoluminescence band at 1.8 eV. The analysis provides strong evidence that the emission is due to recombination in which electrons both from effective-mass donors and from deeper donors recombine with deep centers, the deep centers being vacancy-related defects.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals
78.70.Bj Positron annihilation
61.72.J- Point defects and defect clusters

Radiative recombination and ultralong exciton photoluminescence lifetime in GaN freestanding film via two-photon excitation

Yongchun Zhong, Kam Sing Wong, Weili Zhang, and D. C. Look

Appl. Phys. Lett. 89, 022108 (2006); http://dx.doi.org/10.1063/1.2219399 (3 pages) | Cited 15 times

Online Publication Date: 10 July 2006

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We have measured the photoluminescence (PL) lifetime of a freestanding GaN film using one-photon and two-photon excitations to demonstrate the dramatic difference in exciton recombination dynamics at the surface and in the bulk. An ultralong exciton PL lifetime of 17.2 ns at 295 K is observed from a GaN freestanding film using two-photon excitation, whereas less than 100 ps lifetime is observed for one-photon excitation, suggesting that nonradiative processes from surface defects account for the short PL lifetime measured. A monotonic increase in two-photon excited PL lifetime with increasing temperature and the linear dependence of the exciton lifetime with emission wavelength show good agreement with the theoretical predictions, indicating that radiative recombination dominates for bulk excited state relaxation processes.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
42.70.-a Optical materials
71.35.-y Excitons and related phenomena

Efficient 1.54 μm light emitting diode with nanometer thick polycrystalline Si anode and organic sandwich structure

W. Q. Zhao, G. Z. Ran, G. L. Ma, W. J. Xu, L. Dai, W. M. Liu, P. F. Wang, and G. G. Qin

Appl. Phys. Lett. 89, 022109 (2006); http://dx.doi.org/10.1063/1.2220483 (3 pages) | Cited 2 times

Online Publication Date: 11 July 2006

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This letter reports that the 1.54 μm electroluminescence efficiency of the organic light emitting diode (OLED) with a structure of nanometer thick polycrystalline silicon (NTPS)/NPB/ErQ/AlQ/Al is two orders of magnitude higher than that of the OLED with a structure of thick crystalline silicon/NPB/ErQ/Al, which is similar to the OLED reported in literature [ Curry et al., Appl. Phys. Lett. 77, 2271 (2000) ]. Such an improvement is mainly attributed to the fact that hole injection is controlled by NTPS anode and holes are blocked by AlQ to match electron injection, and a higher light out coupling as well.
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85.60.Jb Light-emitting devices

Nitrogen incorporation during metal organic chemical vapor deposition of ZnO films using a remote Ar/N2 plasma

I. Volintiru, M. Creatore, W. H. van Helvoort, J. L. Linden, and M. C. M. van de Sanden

Appl. Phys. Lett. 89, 022110 (2006); http://dx.doi.org/10.1063/1.2221391 (3 pages) | Cited 6 times

Online Publication Date: 11 July 2006

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Nitrogen-containing zinc oxide films were deposited by the metal organic chemical vapor deposition technique from oxygen/diethylzinc mixtures injected in an argon/nitrogen expanding thermal plasma. Infrared spectroscopy and mass spectrometry measurements suggest that nitrogen is incorporated mostly as –CN and segregated at grain boundaries. The correlation between the presence of nitrile bonds and the formation of HCN in the plasma phase points towards an inherent limitation during such deposition process, i.e., when using carbon-rich precursors in a highly reactive nitrogen environment, such as an Ar/N2 expanding thermal plasma.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
78.30.Fs III-V and II-VI semiconductors
64.75.-g Phase equilibria
61.72.Mm Grain and twin boundaries
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