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23 Aug 2004

Volume 85, Issue 8, pp. 1311-1442

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1338 (2004); http://dx.doi.org/10.1063/1.1785866 (3 pages)

Lori S. Goldner, Scott N. Goldie, Michael J. Fasolka, Francoise Renaldo, Jeeseong Hwang, and Jack F. Douglas
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Two-dimensional metallo-dielectric photonic crystals embedded in anodic porous alumina for optical wavelengths

Osamu Takayama and Michael Cada

Appl. Phys. Lett. 85, 1311 (2004); http://dx.doi.org/10.1063/1.1784047 (3 pages) | Cited 12 times

Online Publication Date: 17 August 2004

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A theoretical study is presented for hexagonal lattice metallic pillar photonic crystals in anodic porous alumina with a lattice constant of 500 nm. The objective of the investigation is to design a two-dimensional metallo-dielectric photonic crystal with an anodic porous alumina template. Optical responses are calculated for silver pillars of radii 100 nm, and 200 nm in porous alumina. The nature of their stop bands and attenuation in the near-infrared region is investigated. Calculations reveal that two-dimensional photonic band gaps for the TM polarization exist at visible wavelengths when the radius is 200 nm.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Microreflectivity characterization of the two-dimensional refractive index distribution of electron-beam-written optical waveguides in germanium-doped flame-hydrolysis silica

S. García Blanco, J. S. Aitchison, C. Hnatovsky, and R. S. Taylor

Appl. Phys. Lett. 85, 1314 (2004); http://dx.doi.org/10.1063/1.1784541 (3 pages) | Cited 6 times

Online Publication Date: 17 August 2004

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In this letter, we report on the detailed refractive index distribution of optical waveguides induced by electron-beam irradiation of Ge-doped flame hydrolysis silica and its variation with dose. The characterization was performed using microreflectivity measurements.
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78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Fe Electron and positron radiation effects
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Infrared surface plasmons in two-dimensional silver nanoparticle arrays in silicon

H. Mertens, J. Verhoeven, A. Polman, and F. D. Tichelaar

Appl. Phys. Lett. 85, 1317 (2004); http://dx.doi.org/10.1063/1.1784542 (3 pages) | Cited 30 times

Online Publication Date: 17 August 2004

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We present two-dimensional arrays of silver nanoparticles embedded in amorphous silicon, fabricated by a sequential Si∕Ag∕Si electron-beam evaporation process. The particle arrays exhibit surface plasmon resonance spectra in the near-infrared (0.9 eV), with tails extending below 0.5 eV. The data are compared with calculations that take into account measured particle size, shape anisotropy, and separation. It is concluded that the large redshift is mainly due to the high refractive index of the matrix, with shape anisotropy and interparticle coupling contributing several tenths of an electron volt. This work enables plasmon-related applications at the telecommunication wavelength of 1.5 μm (0.8 eV).
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
78.30.-j Infrared and Raman spectra
61.46.-w Structure of nanoscale materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Measurement of positive gain on the 1315 nm transition of atomic iodine pumped by O2(a1Δ) produced in an electric discharge

D. L. Carroll, J. T. Verdeyen, D. M. King, J. W. Zimmerman, J. K. Laystrom, B. S. Woodard, N. Richardson, K. Kittell, Mark J. Kushner, and W. C. Solomon

Appl. Phys. Lett. 85, 1320 (2004); http://dx.doi.org/10.1063/1.1784519 (3 pages) | Cited 45 times

Online Publication Date: 17 August 2004

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Laser action at 1315 nm on the I(2P1∕2)→I(2P3∕2) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O2(a1Δ), which is produced using wet-solution chemistry. The system difficulties of chemically producing O2(a1Δ) has motivated investigations into gas phase methods to produce O2(a1Δ) using low-pressure electric discharges. In this letter we report on positive gain on the 1315 nm transition of atomic iodine where the O2(a1Δ) was produced in a flowing electric discharge. The electric discharge was followed by a continuously flowing supersonic cavity that was necessary to lower the temperature of the flow and shift the equilibrium of atomic iodine more in favor of the I(2P1∕2) state. A tunable diode laser system capable of scanning the entire line shape of the (3,4) hyperfine transition of iodine provided the measurements of gain.
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42.55.Ks Chemical lasers
52.80.Tn Other gas discharges

Improvement on the photorefractive performance of a monolithic molecular material by introducing electron traps

Jie Zhang, Zhijian Chen, Yihong Liu, Maomao Huang, Qun Wei, and Qihuang Gong

Appl. Phys. Lett. 85, 1323 (2004); http://dx.doi.org/10.1063/1.1784522 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2004

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The electron-injecting material, tris(8-hydroxyquinoline) aluminum (Alq3), was introduced into photorefractive (PR) samples containing the (9-ethyl-9H-carbazol-3-ylmethylent)-(4-nitrophenyl)-amine (ECYENPA) molecule, which has been proved to possess the fine functions of both electro-optic effect and hole transportation. A small amount of Alq3 forms quantum dots in ECYENPA, serving as electron traps and leading to a great enhancement of the PR effect. A large two-beam coupling coefficient of 424 cm−1 (at 44.6 V∕μm) was observed in a sample doped with 2 wt% of Alq3, in contrast to a value of 232 cm−1 for a sample without Alq3. Moreover, the measured response time was one order of magnitude shorter than that of the undoped sample.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.Qn Polymers; organic compounds

Lasing characteristics of InAs quantum-dot microdisk from 3 K to room temperature

Toshihide Ide, Toshihiko Baba, Jun Tatebayashi, Satoshi Iwamoto, Toshihiro Nakaoka, and Yasuhiko Arakawa

Appl. Phys. Lett. 85, 1326 (2004); http://dx.doi.org/10.1063/1.1787157 (3 pages) | Cited 14 times

Online Publication Date: 17 August 2004

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We fabricated a microdisk laser with five-stacked InAs quantum-dot (QD) active region, and demonstrated the lasing operation from 3 K to room temperature by femtosecond pulsed photopumping. At room temperature, the threshold power was estimated to be 0.75 mW, when the influence of the surface recombination at the disk edge was neglected. The lasing wavelength was 1.2–1.3 μm, which corresponded to excited states of the QDs. The temperature dependence of the threshold, slope efficiency, lasing wavelength, and linewidth are explained by the rapid increase in nonradiative recombination and internal absorption at critical temperatures of 200–230 K.
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42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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Formation of dynamic holograms based on spatial modulation of molecular motions of ferroelectric liquid crystals

Takeo Sasaki, Oki Mochizuki, Yukihito Nakazawa, Godai Fukunaga, Tetsuya Nakamura, and Kazunori Noborio

Appl. Phys. Lett. 85, 1329 (2004); http://dx.doi.org/10.1063/1.1785283 (3 pages) | Cited 5 times

Online Publication Date: 17 August 2004

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The formation of dynamic holograms based on the spatial modulation of the molecular motions of ferroelectric liquid crystals (FLCs) was demonstrated. The consecutive rotational switching motion of FLC molecules under an alternating electric field was modulated by the photoinduced additional electric field built at the interference fringe. This spatially periodic difference in molecular motions of an FLC was confirmed to work as a diffraction grating. Since the motion-mode hologram is stable and the response is very fast when compared to photorefractive polymers, the motion-mode hologram appears to be promising for various photonic applications.
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77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
42.70.Df Liquid crystals
42.40.Eq Holographic optical elements; holographic gratings
77.80.Fm Switching phenomena
42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects

Mechanical model for the generation of acoustic chaos in sonic infrared imaging

Xiaoyan Han, V. Loggins, Zhi Zeng, L. D. Favro, and R. L. Thomas

Appl. Phys. Lett. 85, 1332 (2004); http://dx.doi.org/10.1063/1.1785285 (3 pages) | Cited 7 times

Online Publication Date: 17 August 2004

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We describe a mechanical model for the generation of complex vibrations with fractional “subharmonics” from the contact between a sharply tuned ultrasonic source and a rigid object. The frequency patterns generated by the model mimic the patterns observed in samples undergoing sonic IR imaging. The output of the model is chaotic in the sense that the output appears to lack continuity with respect to the input parameters.
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43.25.Rq Solitons, chaos
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction

On the origin of strain fluctuation in strained-Si grown on SiGe-on-insulator and SiGe virtual substrates

Kentaro Kutsukake, Noritaka Usami, Toru Ujihara, Kozo Fujiwara, Gen Sazaki, and Kazuo Nakajima

Appl. Phys. Lett. 85, 1335 (2004); http://dx.doi.org/10.1063/1.1784036 (3 pages) | Cited 8 times

Online Publication Date: 17 August 2004

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We investigated the microscopic strain fluctuation in strained-Si grown on SiGe-on-insulator (SGOI) and SiGe virtual substrates, and clarified the origins of the strain fluctuation in the strained-Si film. A periodic strain fluctuation, which reflects a cross-hatch pattern of the substrate, was observed in the sample on the virtual substrate. On the other hand, a featureless strain fluctuation with suppressed amplitude was observed in the sample on SGOI substrate. By analyzing the correlation of the Raman peak positions of the Si–Si modes in strained-Si and SiGe, the dominant mechanism of the strain fluctuation in the strained Si film was found to be the compositional fluctuation in underlying SiGe for the sample on SGOI, and the strain fluctuation reflecting the cross-hatch pattern for the sample on the virtual substrate, respectively.
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81.05.Cy Elemental semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.30.Am Elemental semiconductors and insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Db Elemental semiconductors and insulators
68.60.Bs Mechanical and acoustical properties

Near-field polarimetric characterization of polymer crystallites

Lori S. Goldner, Scott N. Goldie, Michael J. Fasolka, Francoise Renaldo, Jeeseong Hwang, and Jack F. Douglas

Appl. Phys. Lett. 85, 1338 (2004); http://dx.doi.org/10.1063/1.1785866 (3 pages) | Cited 2 times

Online Publication Date: 17 August 2004

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We use near-field polarimetry (NFP) to investigate thin-film crystallites of isotactic polystyrene (iPS). NFP micrographs enable quantitative optical characterization of the birefringence in these specimens with subdiffraction-limited resolution, resulting in observations that give: (1) evidence for radial strain in the depletion boundary surrounding the growth front, and (2) a map of local tilt in the crystal axis and/or strain in the amorphous layers above and below the growth plane of the crystallites.
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78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
78.20.Fm Birefringence
68.55.-a Thin film structure and morphology

Cathodoluminescence versus dynamical epitaxy of Ba-ion irradiated α-quartz

S. Dhar, S. Gąsiorek, P. K. Sahoo, U. Vetter, H. Hofsäß, V. N. Kulkarni, and K. P. Lieb

Appl. Phys. Lett. 85, 1341 (2004); http://dx.doi.org/10.1063/1.1784538 (3 pages) | Cited 5 times

Online Publication Date: 17 August 2004

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Doping α-quartz with photoactive ions without destroying its crystalline structure appears to be a promising way to tune its luminescent and structural properties. We have achieved dynamic solid phase epitaxial regrowth and cathodoluminescence of 175 keV Ba-ion irradiated α-quartz in the temperature range from 300 to 1170 K. Rutherford Backscattering Channeling analysis showed that the amorphous layer produced by 1×1015 Ba ions∕cm2 at 300 K had almost disappeared at an implantation temperature of 1123 K. Room temperature cathodoluminescence exhibited dramatic changes in the optical spectra as a function of the implantation temperature and allowed to distinguish between color centers related to quartz, ion-irradiated silica and implanted Ba. Between 770 and 1100 K, room-temperature cathodoluminescence showed a predominant blue and other weak bands connected to various known defects in the �Si-O-Si� network. However, after achieving almost complete solid phase epitaxial recovery, only a violet band at 3.4 eV remained, which we attribute to Ba-related luminescence centers.
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61.82.Ms Insulators
61.80.Jh Ion radiation effects
61.72.up Other materials
61.72.J- Point defects and defect clusters
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
78.60.Hk Cathodoluminescence, ionoluminescence
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
81.15.Np Solid phase epitaxy; growth from solid phases

Thick and adherent cubic boron nitride films grown on diamond interlayers by fluorine-assisted chemical vapor deposition

W. J. Zhang, I. Bello, Y. Lifshitz, K. M. Chan, Y. Wu, C. Y. Chan, X. M. Meng, and S. T. Lee

Appl. Phys. Lett. 85, 1344 (2004); http://dx.doi.org/10.1063/1.1784545 (3 pages) | Cited 22 times

Online Publication Date: 17 August 2004

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Using plasma-enhanced chemical vapor deposition (PECVD) based on fluorine chemistry, the limitations hindering the practical use of cubic boron nitride (cBN) films in mechanical applications have been overcome. The CVD method presented is characteristic with (a) the direct cBN growth on diamond without soft, noncubic BN interface layers, (b) the synthesis of cBN films with extraordinary adhesion to the substrates and high mechanical properties, and (c) the scalable process providing thick, large-area cBN films at high deposition rate even on rough and untreated surfaces. These prime technological properties open the route to the mechanical exploitation of cBN films, particularly in tribological and tool applications. The reduction of the bias voltage in the PECVD process presented to a value of −20 V not only provides high-quality films, but also gives physical insight into the cBN growth mechanism.
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68.35.Np Adhesion
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.05.Ea III-V semiconductors

Proton-beam-induced defect levels in CuInSe2 thin-film absorbers: An investigation on nonradiative electron transitions

Yoji Akaki, Kenji Yoshino, Tetsuo Ikari, Shirou Kawakita, Mitsuru Imaizumi, Shigeru Niki, Keiichiro Sakurai, Shogo Ishizuka, and Takeshi Ohshima

Appl. Phys. Lett. 85, 1347 (2004); http://dx.doi.org/10.1063/1.1784518 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2004

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Electron nonradiative relaxation through the proton-irradiation-induced defects in CuInSe2 solar cell material were investigated by using a piezoelectric photothermal spectroscopy (PPTS). Among the observed three peaks at 1.01, 0.93, and 0.84 eV, it was concluded that the peak at 0.84 eV was due to the proton-irradiation-induced defect. This is because this peak appeared after irradiation with the proton energy of 0.38 MeV and the fluence of 1×1014 cm−2. The peaks at 1.01 and 0.93 eV were attributed to free band-edge exciton and intrinsic defect level, respectively. The intensities for the latter two peaks were not affected by the irradiation. Since the irradiation defect was clearly observed at room temperature, we concluded that the PPTS technique was a very sensitive tool to study the defect level in the irradiated semiconductor thin-film solar cell structures.
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84.60.Jt Photoelectric conversion
71.55.Ht Other nonmetals
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
82.80.Kq Energy-conversion spectro-analytical methods (e.g., photoacoustic, photothermal, and optogalvanic spectroscopic methods)

Cathodoluminescence study of deep ultraviolet quantum wells grown on maskless laterally epitaxial overgrown AlGaN

T. M. Katona, M. D. Craven, J. S. Speck, and S. P. DenBaars

Appl. Phys. Lett. 85, 1350 (2004); http://dx.doi.org/10.1063/1.1777417 (3 pages) | Cited 5 times

Online Publication Date: 17 August 2004

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We have investigated the cathodoluminescence properties of deep UV quantum wells with an emission wavelength of 287 nm grown on maskless lateral epitaxial overgrown Al0.96Ga0.04N. AlN was grown on sapphire via metalorganic chemical vapor deposition. Parallel, periodic trenches were etched in the AlN and Al0.96Ga0.04N was regrown laterally from the unetched mesas. Al0.42Ga0.58N∕Al0.36Ga0.64N quantum wells were then grown on the uncoalesced stripes. Cathodoluminescence was performed on both the laterally overgrown “wings” and unetched “seed” material. Emission from quantum wells located above the wing region was observed to be more intense than emission above the seed region. Depth dependent cathodoluminescence showed that deep level recombination at 3.58 eV (346 nm), 2.77 eV (448 nm), and 2.14 eV (579 nm) was present throughout the n-type Al0.45Ga0.55N and the laterally overgrown unintentionally doped Al0.96Ga0.04N.
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81.07.St Quantum wells
68.65.Fg Quantum wells
78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning

Recrystallization texture, epitaxy, and magnetic properties of electrodeposited FePt on Cu(001)

Erik B. Svedberg, Jonathan J. Mallett, Safak Sayan, Alexander J. Shapiro, William F. Egelhoff, and Thomas Moffat

Appl. Phys. Lett. 85, 1353 (2004); http://dx.doi.org/10.1063/1.1784525 (3 pages) | Cited 7 times

Online Publication Date: 17 August 2004

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A near-equiatomic FePt face-centered-cubic alloy has been grown by electrodeposition onto Cu(001). Annealing at 450 °C results in the onset of a A1 fcc to L10 face-centered-tetragonal phase transformation with a dominant FePt(001)〈100〉∥Cu(001)〈100〉 recrystallization texture, possibly driven by the reduced ordering temperature in an FePtCu intermixed interface region. Further annealing at 650 °C leads to a more complete transformation, and magnetic measurements indicate that high perpendicular coercivities, of up to 10 kOe, are accessible through the recrystallization reaction. The magnetic and structural properties reported in this work may allow electrodeposited FePt to play a leading role in future ultrahigh-density patterned perpendicular magnetic media.
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75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
75.50.Vv High coercivity materials
81.15.Pq Electrodeposition, electroplating
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
81.40.Gh Other heat and thermomechanical treatments
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Spatial correlation-anticorrelation in strain-driven self-assembled InGaAs quantum dots

X.-D. Wang, N. Liu, C. K. Shih, S. Govindaraju, and A. L. Holmes

Appl. Phys. Lett. 85, 1356 (2004); http://dx.doi.org/10.1063/1.1784526 (3 pages) | Cited 21 times

Online Publication Date: 17 August 2004

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We report evidence for the existence of anticorrelation in InGaAs∕GaAs self-assembled quantum dots (QDs). We found that, as a function of the spacer layer thickness, the QDs between the neighboring layers are either vertically correlated (at small spacer thickness) or anticorrelated (at larger spacer thickness). Moreover, in the case when the QDs are antialigned, the size distribution of individual quantum dots becomes more uniform. The implications of this work to the fundamental understanding of the self-assembly process, and the technological applications are discussed.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.37.Ps Atomic force microscopy (AFM)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Measurement of phosphorus segregation in silicon at the atomic scale using scanning tunneling microscopy

L. Oberbeck, N. J. Curson, T. Hallam, M. Y. Simmons, G. Bilger, and R. G. Clark

Appl. Phys. Lett. 85, 1359 (2004); http://dx.doi.org/10.1063/1.1784881 (3 pages) | Cited 20 times

Online Publication Date: 17 August 2004

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In order to fabricate precise atomic-scale devices in silicon using a combination of scanning tunneling microscopy (STM) to position dopant atoms and molecular beam epitaxy to encapsulate the dopants it is necessary to minimize the segregation∕diffusion of dopant atoms during silicon encapsulation. We characterize the surface segregation∕diffusion of phosphorus atoms from a δ-doped layer in silicon after encapsulation at 250 °C and room temperature using secondary ion mass spectrometry (SIMS) and STM. We show that the surface phosphorus density can be reduced to a few percent of the initial δ-doped density if the phosphorus atoms are encapsulated with 5 monolayers of epitaxial silicon at room temperature. We highlight the limitations of SIMS to determine phosphorus segregation at the atomic scale and the advantage of using STM directly.
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81.05.Cy Elemental semiconductors
68.55.A- Nucleation and growth
68.35.Dv Composition, segregation; defects and impurities
68.35.Fx Diffusion; interface formation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Incipient plasticity during nanoindentation at elevated temperatures

Alan C. Lund, Andrea M. Hodge, and Christopher A. Schuh

Appl. Phys. Lett. 85, 1362 (2004); http://dx.doi.org/10.1063/1.1784891 (3 pages) | Cited 22 times

Online Publication Date: 17 August 2004

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The onset of plastic deformation during nanoindentation is studied, focusing upon the effects of temperature variation. Indentations on pure (100)-oriented platinum at 20, 100, and 200 °C reveal that the transition from elastic to plastic deformation occurs at progressively lower stress levels as temperature is increased. Additionally, it is shown that during plastic deformation, higher temperatures promote the discretization of plasticity into sharp bursts of activity. These results are in line with expectations for stress-biased, thermally activated deformation processes such as the nucleation of dislocations or the abrupt release of dislocation entanglements.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations
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Electron accumulation layer at the Cs-covered GaN(0001) n-type surface

G. V. Benemanskaya, V. S. Vikhnin, N. M. Shmidt, G. E. Frank-Kamenetskaya, and I. V. Afanasiev

Appl. Phys. Lett. 85, 1365 (2004); http://dx.doi.org/10.1063/1.1785284 (3 pages) | Cited 10 times

Online Publication Date: 17 August 2004

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We report on the observation of photoemission from the Cs∕GaN(0001) n-type interface by excitation of visible light in the transparency region of GaN. Under Cs adsorption, sharp decrease in photoemission threshold up to 1.3 eV at 0.5 monolayer of Cs is found and shown to be due to formation of a charge accumulation layer in the near-interface region. An interesting phenomenon is revealed, namely, the appearance of an oscillation structure in spectra of photoyield. A model conception taking into account both the formation of charge accumulation layer and occurrence of multiple-beam interference in parallel-sided GaN epilayer is suggested.
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68.43.Mn Adsorption kinetics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.47.Fg Semiconductor surfaces
79.60.Dp Adsorbed layers and thin films

Surface cleaning and annealing effects on Ni∕AlGaN interface atomic composition and Schottky barrier height

S. T. Bradley, S. H. Goss, J. Hwang, W. J. Schaff, and L. J. Brillson

Appl. Phys. Lett. 85, 1368 (2004); http://dx.doi.org/10.1063/1.1785287 (3 pages) | Cited 16 times

Online Publication Date: 17 August 2004

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Internal photoemission spectroscopy reveals changes in the Schottky barrier height of Ni on AlGaN∕GaN high electron mobility transistor structures with premetallization processing conditions and postmetallization ultrahigh-vacuum annealing. These variations in the internal photoemission Schottky barrier height are correlated with AlGaN near-band-edge emissions from low-energy electron-excited nanoluminescence spectroscopy and Ni∕AlGaN interface impurities by secondary ion mass spectrometry. We show that changes in the Schottky barrier height and the appearance of dual barriers are dominated by changes in the local Al mole fraction. Interfacial oxygen and carbon have secondary but systematic effects as well.
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85.30.Tv Field effect devices
68.47.Fg Semiconductor surfaces
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
73.30.+y Surface double layers, Schottky barriers, and work functions
71.55.Eq III-V semiconductors
85.40.Ls Metallization, contacts, interconnects; device isolation
78.55.Cr III-V semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Carrier relaxation in InGaN∕GaN quantum wells with nanometer-scale cluster structures

Hsiang-Chen Wang, Shih-Chun Lin, Yen-Chen Lu, Yung-Chen Cheng, C. C. Yang, and Kung-Jen Ma

Appl. Phys. Lett. 85, 1371 (2004); http://dx.doi.org/10.1063/1.1784033 (3 pages) | Cited 14 times

Online Publication Date: 17 August 2004

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Temperature-dependent femtosecond pump–probe experiments are performed to explore the ultrafast carrier-relaxation processes in an InGaN∕GaN quantum-well sample, in which nanometer-scale cluster structures have been identified. Combined with the time-resolved photoluminescence results, we can identify three stages of carrier relaxation. The fast-decay time, ranging from several hundred femtoseconds to 1 picosecond, corresponds to the process reaching a local quasi-equilibrium condition, in which carriers reach a thermal distribution within one or a few nearby indium-rich clusters. The slow-decay time, ranging from tens to a couple hundred picoseconds, corresponds to the process reaching a global quasi-equilibrium condition, in which carriers reach a thermal distribution among different clusters of various potential minima. In this stage, the mechanism of carrier transport over barriers between clusters dominates the relaxation process. Finally, carrier recombination dominates the relaxation process with the carrier lifetime in the range of a few nanoseconds.
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73.21.Fg Quantum wells
68.65.Fg Quantum wells
78.67.De Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.47.-p Spectroscopy of solid state dynamics

Band-gap modified Al-doped Zn1−xMgxO transparent conducting films deposited by pulsed laser deposition

K. Matsubara, H. Tampo, H. Shibata, A. Yamada, P. Fons, K. Iwata, and S. Niki

Appl. Phys. Lett. 85, 1374 (2004); http://dx.doi.org/10.1063/1.1784544 (3 pages) | Cited 51 times

Online Publication Date: 17 August 2004

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Al-doped Zn1−xMgxO films have been deposited on glass substrates at a substrate temperature of 200 °C by a pulsed laser deposition system. A resistivity of 3×10−4 Ω cm was obtained at x=0.06. Film resistivity was found to increase with further increases in Mg composition. The maximum band gap of films with a resistivity ρ⩽1×10−3 Ω cm was found to be 3.97 eV, demonstrating band-gap engineering possibilities in the range of Eg=3.5–3.97 eV with a resistivity ρ⩽1×10−3 Ω cm. The average transmittance of the films was higher than 90% in the wavelength region λ=400–800 nm, a range suitable for transparent conducting film applications.
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81.05.Dz II-VI semiconductors
68.55.A- Nucleation and growth
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
71.20.Nr Semiconductor compounds
78.40.Fy Semiconductors
81.15.Fg Pulsed laser ablation deposition
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Influence of intensive light exposure on polymer field-effect transistors

J. Ficker, H. von Seggern, H. Rost, W. Fix, W. Clemens, and I. McCulloch

Appl. Phys. Lett. 85, 1377 (2004); http://dx.doi.org/10.1063/1.1784547 (3 pages) | Cited 25 times

Online Publication Date: 17 August 2004

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The influence of intensive light exposure on high performance polymer field-effect transistors containing highly regioregular poly(3-alkylthiophene) as a semiconductor is reported. While the transistors show high stability under ambient air and light, a distinct degradation upon exposure to intensive light could be detected by its impact on the on currents. UV-Vis spectra were used to interpret the current decrease as being caused by a decrease of the conjugation length of the semiconductor, which is supported by IR spectrometry. The role of ambient air, in particular, oxygen, in the degradation process is shown.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.40.Fy Semiconductors
78.40.Me Organic compounds and polymers
78.30.Jw Organic compounds, polymers

Impact ionization coefficients of 4H silicon carbide

T. Hatakeyama, T. Watanabe, T. Shinohe, K. Kojima, K. Arai, and N. Sano

Appl. Phys. Lett. 85, 1380 (2004); http://dx.doi.org/10.1063/1.1784520 (3 pages) | Cited 11 times

Online Publication Date: 17 August 2004

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Anisotropy of the impact ionization coefficients of 4H silicon carbide is investigated by means of the avalanche breakdown behavior of p+n diodes on (0001) and (11math0) 4H silicon carbide epitaxial wafers. The impact ionization coefficients are extracted from the avalanche breakdown voltages and the multiplication of a reverse leakage current, due to impact ionization of these p+n diodes. The breakdown voltage of a p+n diode on a (11math0) wafer is 60% of that on a (0001) wafer, and the extracted impact ionization coefficients of 4H silicon carbide show large anisotropy. We have shown that the anisotropy of the impact ionization coefficients is related to the anisotropy of carrier heating and drift velocity, which are due to the highly anisotropic electronic structure of 4H silicon carbide.
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85.30.Kk Junction diodes
71.20.Nr Semiconductor compounds
72.20.Ht High-field and nonlinear effects
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
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Distribution of activation energies on undoped and SiC-doped superconducting MgB2 wires

E. Martínez and R. Navarro

Appl. Phys. Lett. 85, 1383 (2004); http://dx.doi.org/10.1063/1.1781359 (3 pages) | Cited 7 times

Online Publication Date: 17 August 2004

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The distribution of the activation energies, m(U0), of undoped and SiC-doped MgB2 wires has been estimated from magnetic relaxation measurements using the Hagen-Griessen inversion scheme. Ni-sheathed wires fabricated by the powder-in-tube (PIT) technique, using the ex situ reaction, have been analyzed. The enhancement of the superconducting properties under high magnetic fields (B>2 T) on doped wires is evidenced by the increase of the upper critical, Bc2, and irreversibility, Birr, fields, and by the shift of the pinning energy distribution to higher energy values. The obtained m(U0) distributions might be also explained by a nonlinear current dependence of the pinning energies: U(J,B,T)=[U*(B,T)∕μ]*[(Jc∕J)μ−1] with μ=0.2–0.4.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Op Mixed states, critical fields, and surface sheaths
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Bx Metals, semimetals, and alloys
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