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26 Sep 2005

Volume 87, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 131103 (2005); http://dx.doi.org/10.1063/1.2058213 (3 pages)

M. Feng, N. Holonyak, G. Walter, and R. Chan
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Thermal inhibition of high-power second-harmonic generation in periodically poled LiNbO3 and LiTaO3 crystals

Oleg A. Louchev, Nan Ei Yu, Sunao Kurimura, and Kenji Kitamura

Appl. Phys. Lett. 87, 131101 (2005); http://dx.doi.org/10.1063/1.2056593 (3 pages) | Cited 14 times

Online Publication Date: 19 September 2005

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A coupled thermo-optical model shows strong thermal inhibition of second-harmonic generation (SHG) in periodically poled (PP) LiNbO3 (PPLN) and stoichiometric LiTaO3 (PPSLT) crystals. Three-dimensional simulations performed for a 1.064 μm fundamental wavelength pulsed nanosecond laser beam 150 μm in radius show the onset of significant temperature nonuniformities along and across the irradiated zone, and strong thermal dephasing and inhibition of SHG in these crystals for input powers >10 W. PPSLT is found to have a significant advantage over PPLN due to the higher heat conductance, decreasing these temperature nonuniformities and allowing one to maintain the irradiated zone within the corresponding SHG temperature tolerance range (ΔT ≈ 3 K).
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Bends and splitters in metal-dielectric-metal subwavelength plasmonic waveguides

Georgios Veronis and Shanhui Fan

Appl. Phys. Lett. 87, 131102 (2005); http://dx.doi.org/10.1063/1.2056594 (3 pages) | Cited 197 times

Online Publication Date: 19 September 2005

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We investigate the performance of bends and splitters in metal-dielectric-metal subwavelength plasmonic waveguides. We show that bends and splitters with no additional loss over a very wide frequency range can be designed for metal-dielectric-metal waveguides with center layer thickness small compared to the wavelength. We also introduce the concept of characteristic impedance for such systems to account for their behavior.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Fm Reflectors, beam splitters, and deflectors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Room temperature continuous wave operation of a heterojunction bipolar transistor laser

M. Feng, N. Holonyak, G. Walter, and R. Chan

Appl. Phys. Lett. 87, 131103 (2005); http://dx.doi.org/10.1063/1.2058213 (3 pages) | Cited 48 times

Online Publication Date: 20 September 2005

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Continuous wave laser operation at 25 °C, with simultaneous electrical gain, of an InGaP–GaAs heterojunction bipolar transistor laser, with AlGaAs optical confining layers and an InGaAs recombination quantum well incorporated into the p-type base region, is demonstrated. At laser threshold (IB = 40 mA, VCB = 0, 25 °C), the transistor current gain β = ΔIC/ΔIB in common-emitter operation changes abruptly (2.3→1.2,β>1), with laser modes developing at wavelength λ ∼ 1006 nm. Direct three-port modulation of the transistor laser at 3 GHz is demonstrated for a device with a 2.2 μm emitter width and a 850 μm length between cleaved Fabry–Perot facets (which is the performance of an exploratory device and not near the limits).
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Waveguide array-grating compressors

Sotiris Droulias, Kyriakos Hizanidis, Demetrios N. Christodoulides, and Roberto Morandotti

Appl. Phys. Lett. 87, 131104 (2005); http://dx.doi.org/10.1063/1.2056578 (3 pages) | Cited 5 times

Online Publication Date: 21 September 2005

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We show that efficient optical pulse compression can be achieved when normally dispersive nonlinear waveguide arrays are used in conjunction with dispersive elements such as gratings or other programmable phase filters. Our computations indicate that the compression resulting from such discrete arrays can be of better quality as compared to that obtained traditionally from a single nonlinear waveguide element. The performance of the array-grating compression method is assessed in normally dispersive highly nonlinear AlGaAs array systems.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Wi Nonlinear waveguides
42.79.Dj Gratings

Picosecond time-resolved imaging by nonscanning fluorescence Kerr gate microscope

Tatsuya Fujino, Takuya Fujima, and Tahei Tahara

Appl. Phys. Lett. 87, 131105 (2005); http://dx.doi.org/10.1063/1.2067694 (3 pages) | Cited 4 times

Online Publication Date: 22 September 2005

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A nonscanning picosecond fluorescence Kerr gate microscope has been developed. By applying the optical Kerr gate technique to the fluorescence imaging of microscopic samples, picosecond time-resolved fluorescence images were obtained with 1.4-ps time resolutions and 1-μm space resolutions, without XY scanning of the sample or the excitation light. A demonstrational measurement on an organic microcrystal, perylene, is presented.
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07.60.Pb Conventional optical microscopes
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Jk Polymers and organics

Efficient second harmonic generation from large band gap II-VI semiconductor photonic crystal

H. Yang, P. Xie, S. K. Chan, Z. Q. Zhang, I. K. Sou, G. K. L. Wong, and K. S. Wong

Appl. Phys. Lett. 87, 131106 (2005); http://dx.doi.org/10.1063/1.2061864 (3 pages) | Cited 10 times

Online Publication Date: 23 September 2005

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Dramatic enhancement of second harmonic generation (SHG) near the photonic band edge was observed in a one-dimensional ZnSe/ZnMgS semiconductor photonic crystal (PC) structure. Over two orders of magnitude increase in SHG intensity was observed at the photonic band edge at ∼ 1400 nm compared to the nonphase matching region. The maximum SHG conversion efficiency of 0.8% is observed in only seven micrometers length of crystal. This enhancement came from a combination of large ZnSe second order susceptibility coefficient (χ(2)), high density of optical modes and phase matching of the fundamental and second harmonic waves near the photonic band edge due to modification of the dispersion curve by the PC structure.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors

Curved-microfiber photon coupling for photonic crystal light emitter

In-Kag Hwang, Sun-Kyung Kim, Jin-Kyu Yang, Se-Heon Kim, Sang Hoon Lee, and Yong-Hee Lee

Appl. Phys. Lett. 87, 131107 (2005); http://dx.doi.org/10.1063/1.2061851 (3 pages) | Cited 42 times

Online Publication Date: 23 September 2005

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Highly-efficient evanescent coupling between a photonic crystal resonator and a curved fiber taper is demonstrated. The coupling is utilized to pump the photonic crystal laser and funnel its output photons through a single optical fiber, making it an all-fiber photon source. Photon collection efficiency of ∼ 70% into the fiber and output power of 27 nW are achieved. Highly local pumping results in the record-low threshold of ∼ 35 μW. This scheme provides an ideal platform for an on-demand single photon source based on two-dimensional photonic crystal.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
42.81.Qb Fiber waveguides, couplers, and arrays
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Pseudospark electron beam as an excitation source for extreme ultraviolet generation

Chunqi Jiang, Andras Kuthi, Martin A. Gundersen, and Werner Hartmann

Appl. Phys. Lett. 87, 131501 (2005); http://dx.doi.org/10.1063/1.2053352 (3 pages) | Cited 6 times

Online Publication Date: 19 September 2005

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A xenon pseudospark device is used to generate energetic and intense electron beams (e-beams) that induce extreme ultraviolet (EUV) emission in the range of 11–17 nm. This e-beam-based EUV source is compact, and the device is of interest because it has potentially attractive EUV conversion efficiency and pulse energy requirement, with potential for long lifetime and high repetition-rate operation. The role of e-beam-induced inelastic electronic collisions is considered.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.20.Fs Electron collisions
42.72.Bj Visible and ultraviolet sources
52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Effect of multistep ionizations on the electron temperature in an argon inductively coupled plasma

Min-Hyong Lee and Chin-Wook Chung

Appl. Phys. Lett. 87, 131502 (2005); http://dx.doi.org/10.1063/1.2056592 (3 pages) | Cited 12 times

Online Publication Date: 19 September 2005

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Electron energy distribution functions (EEDFs) are measured in an argon inductively coupled plasma. It is observed that the measured EEDFs are nearly Maxwellian distributions, and the electron temperature derived from the EEDFs decreases with increasing input radio-frequency (rf) power. It appears that additional ionization processes exist. To investigate this decrease in the electron temperature, multistep ionizations are taken into account. An analytical particle balance equation, including the multistep ionizations, are derived. According to the new balance equation, to balance between the total volume ionization and the total surface particle loss, the electron temperature should be decreased with increasing rf power. The comparison between the model and the experiment are presented, and the model agrees well with the experiment.
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52.80.Pi High-frequency and RF discharges
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.25.Jm Ionization of plasmas

Ion mass dependence of the etch yield of SrTiO3 films in reactive plasmas

O. Langlois, L. Stafford, J. Margot, and M. Chaker

Appl. Phys. Lett. 87, 131503 (2005); http://dx.doi.org/10.1063/1.2056611 (3 pages) | Cited 4 times

Online Publication Date: 19 September 2005

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The influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO3 films in Ar/SF6 plasmas is investigated using a parametric approach. The etch yield is found to decrease as the concentration fraction of molecular ions increases. Introducing the concept of effective mass for both ions and SrTiO3, these experimental results are quantitatively explained in the framework of a well-established model originally developed to describe the sputtering of single-atom materials by noble monoatomic ions.
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Mechanisms for sustaining the free-standing plasma beam

Kh. Tarnev, J. Engemann, and D. Korzec

Appl. Phys. Lett. 87, 131504 (2005); http://dx.doi.org/10.1063/1.2067696 (3 pages)

Online Publication Date: 22 September 2005

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A two-dimensional model of a free-standing plasma beam is presented in the letter. Results for spatial distribution of the charged particles and the excited atoms are discussed with stress on the mechanisms sustaining the beam.
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52.50.Dg Plasma sources
52.75.-d Plasma devices
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
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A technique to study the lattice location of hydrogen atoms in silicon by channeling elastic recoil detection analysis

Lin Shao, Yongqiang Wang, J. K. Lee, M. Nastasi, Phillip E. Thompson, N. David Theodore, and J. W. Mayer

Appl. Phys. Lett. 87, 131901 (2005); http://dx.doi.org/10.1063/1.2058200 (3 pages)

Online Publication Date: 19 September 2005

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By combining elastic recoil detection analysis with the channeling technique, energy analysis of forward-scattered math permits determination of the math lattice location. We have used this technique to study the lattice location of hydrogen in a crystalline Si containing a buried boron-doped layer. We showed that hydrogen atoms are trapped at the boron-doped Si layer after hydrogenation and that the majority of the trapped hydrogen atoms are located near bond-center sites.
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61.72.uf Ge and Si
82.80.-d Chemical analysis and related physical methods of analysis
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Atomic-scale structure of self-assembled In(Ga)As quantum rings in GaAs

P. Offermans, P. M. Koenraad, J. H. Wolter, D. Granados, J. M. García, V. M. Fomin, V. N. Gladilin, and J. T. Devreese

Appl. Phys. Lett. 87, 131902 (2005); http://dx.doi.org/10.1063/1.2058212 (3 pages) | Cited 20 times

Online Publication Date: 19 September 2005

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We present an atomic-scale analysis of the indium distribution of self-assembled In(Ga)As quantum rings (QRs) which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. We find that the size and shape of QRs as observed by cross-sectional scanning tunneling microscopy (X-STM) deviate substantially from the ring-shaped islands as observed by atomic force microscopy on the surface of uncapped QR structures. We show unambiguously that X-STM images the remaining quantum dot material whereas the AFM images the erupted quantum dot material. The remaining dot material shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and is responsible for the observed electronic properties of QR structures. These quantum craters have an indium concentration of about 55% and a diameter of about 20 nm which is consistent with the observed electronic radius of QR structures.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.37.Ps Atomic force microscopy (AFM)
81.07.Ta Quantum dots
68.47.Fg Semiconductor surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.16.Dn Self-assembly

Direct experimental observation of a general pattern at the beginning of brittle fracture

Francisco G. Emmerich

Appl. Phys. Lett. 87, 131903 (2005); http://dx.doi.org/10.1063/1.2042538 (3 pages) | Cited 2 times

Online Publication Date: 19 September 2005

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The failures of brittle and ductile materials are governed by the microscopic response around a flaw extremity; but the experimental access to this region of atomic dimensions is extremely difficult. Here we access experimentally this region by using a developed magnetic solid with atomistic characteristics that simulate the crack tip of brittle materials. We show that the general pattern for the beginning of all the ruptures is the reaching of a specific maximum value of the local stress between the unit cells at the extremity of the critical flaw. This work may help simulations of brittle fracture where a criterion is needed to determine when a bond is broken, corresponding to an experimental foundation to those works that use the criterion of a critical atomic snapping distance, starting from which the bond is considered broken.
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46.50.+a Fracture mechanics, fatigue and cracks

Microphotoluminescence mapping of laterally overgrown GaN layers on patterned Si (111) substrates

L. Macht, P. R. Hageman, S. Haffouz, and P. K. Larsen

Appl. Phys. Lett. 87, 131904 (2005); http://dx.doi.org/10.1063/1.2042546 (3 pages) | Cited 10 times

Online Publication Date: 19 September 2005

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Spatial distribution of optical properties of GaN layers grown on patterned Si (111) substrates by maskless metalorganic chemical vapor deposition has been investigated. The Si substrates were prepared with a pattern of 1.5 μm diameter holes at a 3.5 μm distance from each other. The holes were overgrown by GaN until coalescence, creating GaN areas with no substrate underneath. Microphotoluminescence mapping measurements with 0.8 μm lateral resolution show a five-fold increase in luminescence intensity coming from the overhang areas as compared to the layer directly over the substrate. This is accompanied by a slight redshift of the luminescence peak wavelength. Photoelectrochemical etching shows that the dislocation density is much lower in those areas while the photoluminescence redshift is attributed to lesser strain relaxation resulting from a lower dislocation density.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.60.Bs Mechanical and acoustical properties

Effect of Brownian coagulation on the microstructure evolution in rapidly solidified immiscible alloys

J. Z. Zhao, L. L. Gao, and J. He

Appl. Phys. Lett. 87, 131905 (2005); http://dx.doi.org/10.1063/1.2058208 (2 pages) | Cited 2 times

Online Publication Date: 20 September 2005

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The microstructure evolution during a liquid-liquid phase transformation was calculated. The effect of Brownian coagulation on the microstructure development was investigated. The results indicate that Brownian coagulation has a weak effect on the nucleation of the minority phase droplets. For a given alloy composition, its effect on the coalescence of droplets increases with the cooling rate until a critical cooling rate is reached. After that, its effect decreases with the cooling rate. Brownian coagulation leads to a wider and multipeak size distribution of minority phase droplets.
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64.70.Ja Liquid-liquid transitions
64.70.D- Solid-liquid transitions
64.75.-g Phase equilibria
64.60.Q- Nucleation
82.70.-y Disperse systems; complex fluids

Observation of nanoindentation rosettes on {0001}ZnO using scanning Kelvin probe microscopy

M. J. Klopfstein and D. A. Lucca

Appl. Phys. Lett. 87, 131906 (2005); http://dx.doi.org/10.1063/1.2058201 (3 pages) | Cited 7 times

Online Publication Date: 21 September 2005

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Nanoindentation rosettes have been observed by scanning Kelvin probe microscopy on chemomechanical polished and etched {0001}ZnO while under illumination by a broadband light source. The rosette pattern consisted of a central region with a lower surface potential extending beyond the indentation and six arms emanating from this region along the 〈11math0〉 directions. The length of the longest rosette arm was found to be proportional to the square root of the maximum force of indentation minus the average load at which pop-in occurred.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness

Vacancy distribution around isolated implantation sites

B. Ittermann, M. Füllgrabe, H.-J. Stöckmann, F. Kroll, D. Peters, and H. Ackermann

Appl. Phys. Lett. 87, 131907 (2005); http://dx.doi.org/10.1063/1.2061869 (3 pages)

Online Publication Date: 21 September 2005

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Microscopic experimental data on the distribution of vacancies created in isolated implantation events are reported for the model system B in Cu. An interstitial-to-substitutional conversion process of the implanted math ions is utilized to detect lattice damage. We observe vacancy clouds with well-defined edges and a mean radius of 13.5(9) nm. The radial profile of the local vacancy concentration never exceeds 10−4; it is almost flat in the central region before it falls off rapidly, a behavior which cannot be explained by simple binary-collision computer models.
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61.72.J- Point defects and defect clusters
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys

Interface structure and phase of epitaxial SrTiO3 (110) thin films grown directly on silicon

J. H. Hao, J. Gao, Z. Wang, and D. P. Yu

Appl. Phys. Lett. 87, 131908 (2005); http://dx.doi.org/10.1063/1.2061859 (3 pages) | Cited 26 times

Online Publication Date: 22 September 2005

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The interface structure and phase between SrTiO3 (110) on Si (100) have been investigated using high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. The SrTiO3/Si interface was found to be epitaxially crystallized without any amorphous oxide layer. The formation of Sr silicate at the interface was suggested by considering the fact of the core-level spectra of the Si 2p, O 1s, and Sr 3d. Our results suggest that the presence of a coincident site lattice at the interface between Si and a Sr silicate and/or SrTiO3 may help to stabilize SrTiO3 in the epitaxial orientation reported in the work.
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68.35.Ct Interface structure and roughness
79.60.Jv Interfaces; heterostructures; nanostructures

Infrared-to-visible upconversion in thin films of LaEr(MoO4)3

D. M. Bubb, D. Cohen, and S. B. Qadri

Appl. Phys. Lett. 87, 131909 (2005); http://dx.doi.org/10.1063/1.2067712 (3 pages) | Cited 8 times

Online Publication Date: 22 September 2005

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LaEr(MoO4)3 thin films have been grown by pulsed laser deposition. The films were characterized by x-ray diffraction, Rutherford backscattering, and fluorescence measurements. The results show that the deposited films were epitaxial with their c axis oriented along the surface normal. Films illuminated with 980 nm laser light show visible emission spectra. This visible emission arises as a result of the Er 4f−4f transitions and their lifetimes. Such so-called “upconverting phosphors” are important to the development of new chemical and biological sensing applications.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
78.55.Hx Other solid inorganic materials
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
77.80.-e Ferroelectricity and antiferroelectricity
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Global method for measuring stress in polymer fibers at elevated temperatures

G. Anagnostopoulos, A. G. Andreopoulos, J. Parthenios, and C. Galiotis

Appl. Phys. Lett. 87, 131910 (2005); http://dx.doi.org/10.1063/1.2067707 (3 pages)

Online Publication Date: 22 September 2005

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In this work, a methodology is presented for evaluating the interfacial shear stress as well as the corresponding axial stress in full polymer fiber reinforced materials under elevated temperatures. Its validity was confirmed by deriving interfacial shear and axial stress expressions for embedded Kevlar® 29 fibers within an epoxy matrix by means of Raman microscopy. This approach can be established to other systems such as carbon or polyethylene fiber composites, for which the observed Raman bands are both stress and temperature sensitive.
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81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
62.20.-x Mechanical properties of solids
78.30.Jw Organic compounds, polymers

Polychromatic light emission from single InGaN quantum wells grown on pyramidal GaN facets

S. Srinivasan, M. Stevens, F. A. Ponce, and T. Mukai

Appl. Phys. Lett. 87, 131911 (2005); http://dx.doi.org/10.1063/1.2067693 (3 pages) | Cited 16 times

Online Publication Date: 22 September 2005

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We have studied the properties of InGaN/GaN quantum wells grown on epitaxially laterally overgrown GaN stripes. The stripes have a triangular cross section due to {11math2} crystalline facets. We have observed that the integrated light emission from such structures is uniformly polychromatic over a wide range of the visible spectrum. Using cathodoluminescence techniques, we find that the local emission wavelength increases steadily along the facets, in the direction away from the substrate. The gradient in the emission wavelength is related to the dependence of the quantum well width on the relative position along the facet. The continuous variation of the quantum well properties causes a uniform, polychromatic luminescence band. For some conditions, such distribution can resemble solar-white light emission. This approach can be used to produce an integrated white light source for monolithically integrated white light-emitting diodes.
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81.05.Ea III-V semiconductors
81.07.St Quantum wells
78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
78.40.Fy Semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Room-temperature stimulated emission from microcrystalline CsPbCl3 films

S. Kondo, H. Ohsawa, T. Saito, H. Asada, and H. Nakagawa

Appl. Phys. Lett. 87, 131912 (2005); http://dx.doi.org/10.1063/1.2067700 (3 pages) | Cited 6 times

Online Publication Date: 23 September 2005

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Photoluminescence from microcrystalline CsPbCl3 films prepared by crystallization from the amorphous phase is measured under N2 laser excitation. Stimulated emission due to free exciton-free exciton inelastic collision occurs not only at 77 K (as reported very recently) but also at room temperature (RT). The intensity of the stimulated emission more rapidly increases with pumping intensity at RT than at 77 K, although the threshold is higher at the former temperature (600 kW cm−2) than at the latter (240 kW cm−2). This demonstration of the stimulated emission at RT from metal halides encourages us to explore laser media in metal halides because of their material abundance.
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78.66.Li Other semiconductors
78.45.+h Stimulated emission
71.35.-y Excitons and related phenomena
78.55.Hx Other solid inorganic materials
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Band gap reduction in GaNSb alloys due to the anion mismatch

T. D. Veal, L. F. J. Piper, S. Jollands, B. R. Bennett, P. H. Jefferson, P. A. Thomas, C. F. McConville, B. N. Murdin, L. Buckle, G. W. Smith, and T. Ashley

Appl. Phys. Lett. 87, 132101 (2005); http://dx.doi.org/10.1063/1.2058224 (3 pages) | Cited 10 times

Online Publication Date: 19 September 2005

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The structural and optoelectronic properties in GaNxSb1−x alloys (0 ⩽ x<0.02) grown by molecular-beam epitaxy on both GaSb substrates and AlSb buffer layers on GaAs substrates are investigated. High-resolution x-ray diffraction (XRD) and reciprocal space mapping indicate that the GaNxSb1−x epilayers are of high crystalline quality and the alloy composition is found to be independent of substrate, for identical growth conditions. The band gap of the GaNSb alloys is found to decrease with increasing nitrogen content from absorption spectroscopy. Strain-induced band-gap shifts, Moss-Burstein effects, and band renormalization were ruled out by XRD and Hall measurements. The band-gap reduction is solely due to the substitution of dilute amounts of highly electronegative nitrogen for antimony, and is greater than observed in GaNAs with the same N content.
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73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Very high time-of-flight mobility in the columnar phases of a discotic liquid crystal

Hiroaki Iino, Jun-ichi Hanna, Richard J. Bushby, Bijan Movaghar, Benjamin J. Whitaker, and Michael J. Cook

Appl. Phys. Lett. 87, 132102 (2005); http://dx.doi.org/10.1063/1.2056608 (3 pages) | Cited 52 times

Online Publication Date: 19 September 2005

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1,4,8,11,15,18,22,25-Octaoctylphthalocyanine shows the highest time-of-flight (“long-range”) hole mobility so far reported for the columnar phase of a discotic liquid crystal. Unlike most other high long-range mobility columnar discotics, there is no clear evidence from x-ray diffraction of high order.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.30.-v Liquid crystals
72.80.Le Polymers; organic compounds (including organic semiconductors)
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