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15 Mar 2010

Volume 107, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 107, 061802 (2010); http://dx.doi.org/10.1063/1.3340518 (13 pages)

Vojtěch Minárik, Michal Beneš, and Jan Kratochvíl
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back to top Lasers, Optics, and Optoelectronics

Control of an electrowetting-based beam deflector

Bart de Boer, Freek Suijver, Mischa Megens, Szabolcs Deladi, and Stein Kuiper

J. Appl. Phys. 107, 063101 (2010); http://dx.doi.org/10.1063/1.3319649 (5 pages) | Cited 2 times

Online Publication Date: 16 March 2010

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We experimentally demonstrate the feasibility of a small, low-power beam deflector based on electrowetting. The beam deflector deflects light by refraction at the flat interface (meniscus) between two immiscible and density-matched liquids, namely, a nonpolar oil mixture and an aqueous salt solution. The liquids are contained in a square pyramidal frustum with electrode-covered faces. The electrodes can be separately driven by voltage sources in order to control the contact angle between the meniscus and the frustum faces. By controlling the voltage on all four electrodes, a flat meniscus is obtained that can be tilted independently in two perpendicular directions. We present a capacitance-based feedback driving scheme and demonstrate that it can be used for accurate control of the meniscus shape and tilt. Independent, continuous, and accurate beam steering through an angle of ±6° was achieved on two deflection axes.
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42.79.-e Optical elements, devices, and systems
42.25.Gy Edge and boundary effects; reflection and refraction

Growth and characteristics of GaInN/GaInN multiple quantum well light-emitting diodes

Wonseok Lee, Min-Ho Kim, Di Zhu, Ahmed N. Noemaun, Jong Kyu Kim, and E. F. Schubert

J. Appl. Phys. 107, 063102 (2010); http://dx.doi.org/10.1063/1.3327425 (6 pages) | Cited 4 times

Online Publication Date: 16 March 2010

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We demonstrate GaInN multiple quantum well (MQW) light-emitting diodes (LEDs) having ternary GaInN quantum barriers (QBs) instead of conventional binary GaN QBs for a reduced polarization mismatch between QWs and QBs and an additional separate confinement of carriers to the MQW active region. In comparison with GaInN LEDs with conventional GaN QBs, the GaInN/GaInN LEDs show a reduced blueshift of the peak wavelength with increasing injection current and a reduced forward voltage. In addition, we investigate the density of pits emerging on top of the MQW layer that are correlated with V-defects and act as a path for the reverse leakage current. The GaInN/GaInN MQW structure has a lower pit density than the GaInN/GaN MQW structure as well as a lower reverse leakage current. Finally, the GaInN/GaInN MQW LEDs show higher light output power and external quantum efficiency at high injection currents compared to the conventional GaInN/GaN MQW LEDs. We attribute these results to the reduced polarization mismatch and the reduced lattice mismatch in the GaInN/GaInN MQW active region.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
72.20.-i Conductivity phenomena in semiconductors and insulators
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Heterogeneous integration and precise alignment of InP-based photonic crystal lasers to complementary metal-oxide semiconductor fabricated silicon-on-insulator wire waveguides

T. J. Karle, Y. Halioua, F. Raineri, P. Monnier, R. Braive, L. Le Gratiet, G. Beaudoin, I. Sagnes, G. Roelkens, F. van Laere, D. Van Thourhout, and R. Raj

J. Appl. Phys. 107, 063103 (2010); http://dx.doi.org/10.1063/1.3319667 (8 pages) | Cited 9 times

Online Publication Date: 18 March 2010

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The integration of two-dimensional III-V InP-based photonic crystal and silicon wire waveguides is achieved through an accurate alignment of the two optical levels using mix-and-match deep ultraviolet (DUV)/electron beam lithography. The adhesively bonded structures exhibit an enhancement of light emission at frequencies where low group velocity modes of the photonic crystal line defect waveguides occur. Pulsed laser operation is obtained from these modes at room temperature under optical pumping. The laser light is coupled out of the Si waveguide via grating couplers directly to single mode fiber.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings

Room temperature photonic crystal band-edge lasing from nanopillar array on GaN patterned by nanosphere lithography

Wai Yuen Fu, Kenneth Kin-Yip Wong, and H. W. Choi

J. Appl. Phys. 107, 063104 (2010); http://dx.doi.org/10.1063/1.3353974 (4 pages) | Cited 2 times

Online Publication Date: 18 March 2010

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An ordered GaN nanopillar array fabricated by nanosphere lithography exhibited room temperature photopumped lasing via the photonic crystal band-edge effect. With a monolayer of self-assembled nanospheres as hard mask, the ordered pattern was transferred to the sample to form nanopillars by inductively coupled plasma dry etch. Under pulsed optical excitation, room temperature lasing with a low lasing threshold of 30 mJ/cm2 was achieved. The dominant lasing peak, centered at 415.6 nm, corresponds to a band-edge mode at the Γ-point of the band diagram. A Q factor in the range of 600–700, and spontaneous emission coupling factor of 0.021 were evaluated.
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42.70.Qs Photonic bandgap materials
81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography
78.66.Fd III-V semiconductors

Resonant transmission of electromagnetic waves through two-dimensional photonic quasicrystals

Yair Neve-Oz, Therese Pollok, Sven Burger, Michael Golosovsky, and Dan Davidov

J. Appl. Phys. 107, 063105 (2010); http://dx.doi.org/10.1063/1.3329542 (5 pages) | Cited 3 times

Online Publication Date: 18 March 2010

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We present numerical simulations of electromagnetic millimeter-wave propagation in a two-dimensional lattice of dielectric rods arranged in a tenfold Penrose tiling. We find (i) isotropic photonic band gap as expected for quasicrystals and (ii) localized states. We demonstrate that the high frequency edge of the second band gap is characterized by a very small refractive index (fast light). We study the transmission of electromagnetic waves in the frequency range corresponding to fast light and demonstrate that it is related to tunneling through localized states. We use the fast light phenomenon to design a focusing device—a planoconcave lens.
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78.70.Gq Microwave and radio-frequency interactions
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials

Submicron surface patterning by laser ablation with short UV pulses using a proximity phase mask setup

B. Borchers, J. Bekesi, P. Simon, and J. Ihlemann

J. Appl. Phys. 107, 063106 (2010); http://dx.doi.org/10.1063/1.3331409 (5 pages)

Online Publication Date: 18 March 2010

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A new approach for the generation of large-area periodic surface structures on different materials, like polymers and semiconductors, by direct laser ablation is presented. The surfaces were illuminated with the interference pattern emerging in close proximity behind a laser irradiated phase mask. In the experiments, nanosecond and picosecond laser pulses at 248 nm were applied. To prevent contamination or damage of the phase mask caused by the ablated material, the mask is protected by a thin water film or a thin quartz plate. In addition we present a technique to eliminate a lateral variation of the generated structures due to insufficient alignment precision of the workpiece.
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81.65.Cf Surface cleaning, etching, patterning
68.35.bg Semiconductors
68.35.bm Polymers, organics
79.20.Eb Laser ablation
61.82.-d Radiation effects on specific materials
78.47.J- Ultrafast spectroscopy (<1 psec)
81.65.-b Surface treatments

Self-heating effect in 1.3 μm p-doped InAs/GaAs quantum dot vertical cavity surface emitting lasers

D. W. Xu, C. Z. Tong, S. F. Yoon, L. J. Zhao, Y. Ding, and W. J. Fan

J. Appl. Phys. 107, 063107 (2010); http://dx.doi.org/10.1063/1.3309954 (6 pages)

Online Publication Date: 22 March 2010

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The self-heating effect in 1.3 μm p-doped InAs/GaAs quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) has been investigated using a self-consistent theoretical model. Good agreement is obtained between theoretical analysis and experimental results under pulsed operation. The results show that in p-doped QD VCSELs, the output power is significantly influenced by self-heating. About 60% of output power is limited by self-heating in a device with oxide aperture of 5×6 μm2. This value reduces to 55% and 48%, respectively, as the oxide aperture increases to 7×8 and 15×15 μm2. The temperature increase in the active region and injection efficiency of the QDs are calculated and discussed based on the different oxide aperture areas and duty cycle.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Model of laser-induced temperature changes in solid-state optical refrigerators

W. M. Patterson, M. Sheik-Bahae, R. I. Epstein, and M. P. Hehlen

J. Appl. Phys. 107, 063108 (2010); http://dx.doi.org/10.1063/1.3277009 (9 pages) | Cited 4 times

Online Publication Date: 29 March 2010

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We present an efficient and numerically stable method to calculate time-dependent, laser-induced temperature distributions in solids and provide a detailed description of the computational procedure and its implementation. This study combines the two-dimensional heat equation with laser-induced heat generation and temperature-dependent luminescence. The time-dependent optical response of a system is obtained numerically by the Crank–Nicolson method. This general model is applied to the specific case of optical refrigeration in ytterbium (Yb3+) doped fluorozirconate glass (ZBLAN). The laser-induced temperature change upon optical pumping and the respective transient luminescence response are calculated and compared to experimental data. The model successfully predicts the zero-crossing temperature, the net quantum efficiency, and the functional shape of the transients. We find that the laser-cooling transients have a fast and a slow component that are determined by the excited-state lifetime of the luminescent ion and the thermal properties of the bulk, respectively. The tools presented here may find application in the design of a wide range of optical and optoelectronic devices.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
78.55.Hx Other solid inorganic materials

Label-free detection of oligonucleotide microarrays by oblique-incidence reflectivity difference method

Xu Wang, Kun Yuan, Heng Lu, Juan Wen, Huibin Lu, Kuijuan Jin, Yueliang Zhou, Guozhen Yang, Wei Li, and Kangcheng Ruan

J. Appl. Phys. 107, 063109 (2010); http://dx.doi.org/10.1063/1.3327447 (4 pages) | Cited 4 times

Online Publication Date: 30 March 2010

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Hybridizations between labeled or label-free targets and corresponding 21-base oligonucleotide probes, concentrations of which range from 0.39 to 50 μM, are detected by oblique-incidence reflectivity difference (OI-RD) method and fluorescence detection. The experimental results demonstrate that the OI-RD method can be utilized to not only distinguish whether the hybridization of oligonucleotides happened but also directly tell the different concentrations of the labeled and unlabeled oligonucleotides on the microarrays. The analysis with a classical three-layer model suggests that single-strand DNA tends to lie on epoxy-functionalized glass slide while the double-strand DNA prefers to have a tilted angle with respect to the slide in our experimental situation. The label-free detection of hybridization of oligonucleotides declares that OI-RD is a promising method for label-free and high-throughput detection of the biological microarrays.
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87.15.H- Dynamics of biomolecules
33.50.Dq Fluorescence and phosphorescence spectra
87.80.-y Biophysical techniques (research methods)
36.20.Ey Conformation (statistics and dynamics)
87.14.gk DNA

Analysis of photoconductive gain as it applies to single-photon detection

M. A. Rowe, G. M. Salley, E. J. Gansen, S. M. Etzel, S. W. Nam, and R. P. Mirin

J. Appl. Phys. 107, 063110 (2010); http://dx.doi.org/10.1063/1.3359684 (5 pages) | Cited 1 time

Online Publication Date: 30 March 2010

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We detail a mathematical framework for photoconductive gain applied to the detection of single photons. Because photoconductive gain is derived from the ability to measure current change for an extended period, its magnitude is reduced as detection speed is increased. We theoretically show that high-speed detection is still possible as long as the noise spectrum of the device is 1/f in nature. Using signal analysis techniques, we develop tools to apply to device noise spectra to determine the performance of single-photon detectors that utilize photoconductive gain. We show that there is no speed penalty when one considers the signal-to-noise ratio for the fundamental 1/f noise typical of high electron mobility transistors. We outline a technique for quickly characterizing a detector’s sensitivity and speed through purely electrical measurements of the device’s noise spectra. Consequently, the performance of the detector can be determined and optimized without conducting optical measurements. Finally, we employ this analysis to a quantum dot, optically gated field-effect transistor and verify our results with optical measurements.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Tv Field effect devices
81.07.Ta Quantum dots
back to top Plasmas and Electrical Discharges

Time-resolved imaging of millimeter waves using visible continuum from the positive column of a Cs–Xe dc discharge

M. S. Gitlin, V. V. Golovanov, A. G. Spivakov, A. I. Tsvetkov, and V. V. Zelenogorskiy

J. Appl. Phys. 107, 063301 (2010); http://dx.doi.org/10.1063/1.3327218 (11 pages) | Cited 2 times

Online Publication Date: 16 March 2010

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We present a high-sensitivity technique for time-resolved imaging of millimeter waves (MMWs) using the visible continuum (VC) from the positive column (PC) of a medium-pressure Cs–Xe dc discharge. For the MMW imaging application, a uniform plasma slab of the PC of a Cs–Xe discharge with 10×8 cm2 aperture and 2 cm in thickness was generated for 45 Torr xenon. The imaging technique is based on the fact that the intensity of the e-Xe bremsstrahlung continuum from the PC increases in the visible region when the electrons in the plasma are heated by MMWs. It is shown that in the MMW intensity range from zero to the threshold of the microwave-induced plasma breakdown, the intensity of the VC from the PC of a Cs–Xe discharge increases approximately as a second-order polynomial function of the MMW intensity. The obtained experimental data agree well with our calculations of the dependence of the VC intensity on electron temperature. The Ka-band MMW field patterns at the output of conical horn antennas and in the quasioptical beam were imaged using the discharge technique. It is shown that the technique can be used for time-resolved measurement of the profiles of watt- and subwatt-level MMWs. An energy flux sensitivity of the technique of about 10 μJ/cm2 in the Ka-band was demonstrated. The temporal resolution of the technique is about 0.8 μs. Our modeling of the transient behavior of the electron temperature in the PC shows that the time history of the electron temperature variation coincides well with the measured time history of the VC intensity variation.
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52.70.Gw Radio-frequency and microwave measurements
52.80.Pi High-frequency and RF discharges
52.25.-b Plasma properties
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons

Substantial increase in acceleration potential of pyroelectric crystals

W. Tornow, S. M. Lynam, and S. M. Shafroth

J. Appl. Phys. 107, 063302 (2010); http://dx.doi.org/10.1063/1.3309841 (4 pages) | Cited 2 times

Online Publication Date: 16 March 2010

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We report on a substantial increase in the acceleration potential achieved with a LiTaO3 pyroelectric crystal. With a single 2.5 cm diameter and 2.5 cm long z-cut crystal without electric field-enhancing nanotip we produced positive ion beams with maximal energies between 300 and 310 keV during the cooling phase when the crystal was exposed to 5 mTorr of deuterium gas. These values are about a factor of 2 larger than previously obtained with single pyroelectric crystals.
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77.70.+a Pyroelectric and electrocaloric effects
29.25.Dz Neutron sources

Stark broadening measurement of the electron density in an atmospheric pressure argon plasma jet with double-power electrodes

Muyang Qian, Chunsheng Ren, Dezhen Wang, Jialiang Zhang, and Guodong Wei

J. Appl. Phys. 107, 063303 (2010); http://dx.doi.org/10.1063/1.3330717 (5 pages) | Cited 9 times

Online Publication Date: 17 March 2010

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Characteristics of a double-power electrode dielectric barrier discharge of an argon plasma jet generated at the atmospheric pressure are investigated in this paper. Time-averaged optical emission spectroscopy is used to measure the plasma parameters, of which the excitation electron temperature is determined by the Boltzmann's plot method whereas the gas temperature is estimated using a fiber thermometer. Furthermore, the Stark broadening of the hydrogen Balmer Hβ line is applied to measure the electron density, and the simultaneous presence of comparable Doppler, van der Waals, and instrumental broadenings is discussed. Besides, properties of the jet discharge are also studied by electrical diagnosis. It has been found that the electron densities in this argon plasma jet are on the order of 1014 cm−3, and the excitation temperature, gas temperature, and electron density increase with the applied voltage. On the other hand, these parameters are inversely proportional to the argon gas flow rate.
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52.75.-d Plasma devices
52.25.-b Plasma properties

Analytic model for the breakup of a coasting beam with space charge in isochronous accelerators

Yuanjie Bi, Tianjue Zhang, Chuanxiang Tang, Yongsheng Huang, and Jianjun Yang

J. Appl. Phys. 107, 063304 (2010); http://dx.doi.org/10.1063/1.3340865 (6 pages) | Cited 1 time

Online Publication Date: 18 March 2010

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An analytical model based on the negative mass instability is introduced in this paper to explain the formation of the breakup of a coasting beam into small clusters in isochronous machines such as the case observed by Pozdeyev and Rodriguez in a small isochronous ring. Solving Poisson’s equation in both charge and vacuum regions with the longitudinal beam density perturbation, the coherent radial space charge force which decreases the transition gamma is obtained. It is found that the modified transition gamma depends on the wave number of the density perturbation, longitudinal beam density distribution, beam intensity, and beam size. By combining the longitudinal space charge force caused by the perturbation and the modified transition gamma, a dispersion relation for a monoenergetic beam is derived and evaluated for the fastest-growing instability mode in terms of the beam parameters, such as energy, bunch length, intensity, and emittance. The fastest-growing negative mass mode number, which determines not only the cluster number but also the growth rate of the instability, is proportional to the orbit radius and inversely proportional to the initial beam size. With the growth of the instability, the particles at the points of local minimum density move to the ones of local maximum density, with the transition gamma increasing. Since the growth rate depends on the longitudinal density distribution, therefore, instead of a constant growth rate, our model shows that the growth rate decreases with time. The results above can be applied to both short and long wavelength limits. As an important application of this theory, the beam breakup effect in the isochronous cyclotron CYCIAE-100 is predicted.
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29.27.Fh Beam characteristics
29.20.Ej Linear accelerators
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Optimization and analysis of shape of coaxial electrode for microwave plasma in water

Yoshiaki Hattori, Shinobu Mukasa, Shinfuku Nomura, and Hiromichi Toyota

J. Appl. Phys. 107, 063305 (2010); http://dx.doi.org/10.1063/1.3319616 (8 pages) | Cited 5 times

Online Publication Date: 18 March 2010

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The effect of the shape of the electrode to generate 2.45 GHz microwave plasma in pure water is examined. Three variations of a common coaxial electrode are proposed, and compared according to the power required for plasma ignition and the position of plasma ignition in pure water at 6 kPa using a high-speed camera. These coaxial electrodes are calculated using three-dimensional finite-difference time-domain method calculations. The superior shape of coaxial electrode is found to be one with a flat plane on the tip of the inner electrode and dielectric substance located below the tip of the outer electrode. The position of the plasma ignition is related to the shape of the coaxial electrode. By solving the heat-conduction equation of water around the coaxial electrode taking into account the absorption of the microwave energy, the position of the plasma ignition is found to be not where electric field is the largest, but rather where temperature is maximized.
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52.80.Wq Discharge in liquids and solids
02.70.Bf Finite-difference methods
84.40.Az Waveguides, transmission lines, striplines
52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges

Simulation of redeposition during platinum etching in argon plasmas

J. Saussac, J. Margot, L. Stafford, and M. Chaker

J. Appl. Phys. 107, 063306 (2010); http://dx.doi.org/10.1063/1.3343346 (5 pages) | Cited 1 time

Online Publication Date: 19 March 2010

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The influence of redeposition on the space and time evolution of feature profiles during platinum etching in high-density argon plasmas is examined using simulations. The simulator takes into account redeposition resulting from either direct sticking of the sputtered species on the materials walls (line-of-sight redeposition) or from sputtered species returning from plasma (indirect redeposition). Overall, the simulator successfully reproduces experimental profiles sputter etched in platinum, in particular V-shaped profiles reported in literature. From comparison between experimental and simulated profiles at very low pressure, Pt/resist sticking probability was estimated to be 0.1 and the angular spread of the sputtered atom distribution was predicted to be about ±50°. It was further found that indirect redeposition becomes crucial at higher pressure for explaining the amount of redeposited matter.
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81.65.Cf Surface cleaning, etching, patterning
81.15.Cd Deposition by sputtering
52.77.Bn Etching and cleaning

Indium substituted PrCo5 sintered magnet: A microstructure view

W. F. Li, A. M. Gabay, C. Ni, and G. C. Hadjipanayis

J. Appl. Phys. 107, 063307 (2010); http://dx.doi.org/10.1063/1.3331405 (4 pages) | Cited 1 time

Online Publication Date: 22 March 2010

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Indium addition in PrCo5 magnets can facilitate their sintering and improve their coercivity significantly. Transmission electron microscope studies showed the presence of indium-rich phase PrCo2In, at the intergranular region in the sintered Pr18Co81.5In0.5 magnets annealed at 800 and 950 °C. Another new ternary phase, Pr3Co9In2, appeared only in magnets annealed at 950 °C. Both of these phases are believed to be helpful to improve the sintering behavior of the magnets. Especially, the Pr3Co9In2 phase is observed in the form of a thin layer along the grain boundaries, which is believed to improve the magnetic performance of the magnet.
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61.72.Mm Grain and twin boundaries
75.50.Ww Permanent magnets
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Optical and electrical diagnostics of an atmospheric pressure room-temperature plasma plume

Y. Xian, X. Lu, Z. Tang, Q. Xiong, W. Gong, D. Liu, Z. Jiang, and Y. Pan

J. Appl. Phys. 107, 063308 (2010); http://dx.doi.org/10.1063/1.3360932 (4 pages) | Cited 6 times

Online Publication Date: 29 March 2010

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Cold plasmas have recently received great attention. In this paper, optical and electrical diagnostics are carried out on a reliable and user-friendly plasma plume. A simple electrical model is used to simulate the electrical characteristics of the device. The plasma is represented by a resistor connected in parallel with a capacitor, an inductor, and another resistor, which are connected in series. The simulated current-voltage waveforms have very good agreement with experimental measurements. Besides, the emission spectra of the plasma are also studied. It shows that, when Ar is used as working gas, there is strong OH (hydroxyl radical) emission and the emission intensities of the N2 emission bands are more than three times higher than that of He. On the contrary, when He is used as working gas, the emission intensities of N2+ band are much stronger. Detail analyses on these observations are presented.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements
52.65.-y Plasma simulation
52.75.-d Plasma devices
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Microstructural properties and dislocation evolution on a GaN grown on patterned sapphire substrate: A transmission electron microscopy study

Y. H. Kim, H. Ruh, Y. K. Noh, M. D. Kim, and J. E. Oh

J. Appl. Phys. 107, 063501 (2010); http://dx.doi.org/10.1063/1.3327004 (4 pages) | Cited 5 times

Online Publication Date: 16 March 2010

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The microstructural properties of a GaN layer grown on a patterned sapphire substrate (PSS) were studied in detail using transmission electron microscope techniques to determine dislocation and growth behaviors. Regular and uniform recrystallized GaN islands were observed on the protruding pattern. On a flat sapphire surface, the crystallographic orientation relationship of 〈math2math0〉GaN on FS//〈1math00〉sapphire and {1math01}GaN on FS//{1math13}sapphire existed between the GaN and the substrate. On the other hand, the orientation relationship of 〈math2math0〉GaN layer//〈math2math0〉GaN island on IS//〈1math00〉sapphire and {1math01}GaN layer//{0002}GaN island on IS//{1math13}sapphire was confirmed among the GaN layer, the recrystallized GaN islands on an inclined sapphire surface and the PSS. The flat surface among the protruding patterns began to fill rapidly with GaN. Then, the GaN gradually overgrew the protruding pattern and coalesced near the summit as the growth time increased. The generation of threading dislocations was observed in the vicinity of the coalescence points near the top of the protruding patterns.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.J- Morphology of films
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

High precision thermal stress study on flip chips by synchrotron polychromatic x-ray microdiffraction

Kai Chen, N. Tamura, Wei Tang, M. Kunz, Yi-Chia Chou, K. N. Tu, and Yi-Shao Lai

J. Appl. Phys. 107, 063502 (2010); http://dx.doi.org/10.1063/1.3309750 (5 pages) | Cited 1 time

Online Publication Date: 16 March 2010

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The bending and residual stress of flip chips caused by the mismatch of thermal expansion between the chip and the substrate have been measured by polychromatic microfocused synchrotron x-ray beam. Precise orientation information as a function of position on the chip was obtained from Laue diffraction patterns, so that the bending angle with respect to a reference position at the center of the chip can be calculated at each position. This in turn allows deducing the local curvature of the entire flip chip. Local stress distribution was then mapped by applying a modified Stoney’s stress-strain equation to the measured curvature. Our study shows that thermal stress on the circuits and the solder joints in a flip chip strongly depend on temperature and the distance from the center of the chip, indicating that interconnects at the corner and edge of a flip chip are of reliability concerns.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

In situ x-ray diffraction studies on epitaxial VO2 films grown on c-Al2O3 during thermally induced insulator-metal transition

Kunio Okimura, Joe Sakai, and Shriram Ramanathan

J. Appl. Phys. 107, 063503 (2010); http://dx.doi.org/10.1063/1.3327422 (5 pages) | Cited 16 times

Online Publication Date: 16 March 2010

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The structural phase transition (SPT) of VO2 films epitaxially grown on c-Al2O3 substrates by pulsed laser deposition and reactive sputtering was investigated by in situ temperature-controlled x-ray diffraction (XRD) across metal-insulator transition (MIT). An intermediate insulator phase was observed between room temperature monoclinic phase and high temperature metallic tetragonal phase. Gaussian curve fittings for measured XRD patterns revealed a significant contribution of the intermediate phase covering wide temperature range across MIT. Polycrystalline VO2 films grown on Si substrates revealed pure rutile phase after MIT in contrast with the epitaxial films on c-Al2O3 substrates. Strained structure of the VO2 films grown on c-Al2O3 substrates could be a mechanism for the formation of such intermediate phase known as monoclinic M2 phase. Presence of the intermediate insulator phase in highly oriented VO2 films may be an important factor in understanding the relation between MIT and SPT.
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68.55.aj Insulators
71.30.+h Metal-insulator transitions and other electronic transitions
81.15.Cd Deposition by sputtering
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
64.70.K- Solid-solid transitions

Strain relaxation in high Ge content SiGe layers deposited on Si

G. Capellini, M. De Seta, Y. Busby, M. Pea, F. Evangelisti, G. Nicotra, C. Spinella, M. Nardone, and C. Ferrari

J. Appl. Phys. 107, 063504 (2010); http://dx.doi.org/10.1063/1.3327435 (8 pages) | Cited 11 times

Online Publication Date: 16 March 2010

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We have used Raman spectroscopy, transmission electron microscopy, x-ray diffraction, and x-ray photoemission spectroscopy to investigate strain relaxation mechanism of Si0.22Ge0.78 heteroepitaxial layer deposited on Si substrates in tensile, neutral, and compressive strain conditions. The three regimes have been obtained by interposing between the SiGe layer and the substrate a fully relaxed Ge layer, a partially relaxed Ge layer, or growing directly the alloy on Si. We found that the deposition of a Ge buffer layer prior to the growth of the SiGe is very promising in view of the realization of thin virtual substrates on silicon to be used for the deposition of strain-controlled high Ge content SiGe alloys. We demonstrate that this is mainly due to the strain relaxation mechanism in the Ge layer occurring via insertion of pure edge 90° misfit dislocations (MDs) and to the confinement of threading arms in to the Ge layer due to a second MD network formed at the SiGe/Ge heterointerface.
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68.60.Bs Mechanical and acoustical properties
68.55.ag Semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.30.-j Infrared and Raman spectra

Near-infrared quantum cutting via cooperative energy transfer in Gd2O3:Bi3+,Yb3+ phosphors

X. Y. Huang and Q. Y. Zhang

J. Appl. Phys. 107, 063505 (2010); http://dx.doi.org/10.1063/1.3354063 (4 pages) | Cited 13 times

Online Publication Date: 19 March 2010

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An efficient near-infrared (NIR) quantum-cutting (QC) by converting broadband ultraviolet (UV) into NIR via cooperative down-conversion (CD) has been demonstrated in Gd2O3:Bi3+,Yb3+ phosphors. Upon excitation of UV photon varying from 320–390 nm, NIR emissions has been obtained from transitions of the transition-metal Bi3+:3P1 level to the rare-earths Yb3+:2F5/2 level. The authors have analyzed the measured luminescence spectra and decay lifetimes and proposed a mechanism to rationalize the CD effect. Application of the broadband NIR-QC phosphors might greatly enhance response of silicon-based solar cells by means of down-conversion of UV part of the solar spectrum to NIR photons with a twofold increase in the photon number.
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88.40.H- Solar cells (photovoltaics)
78.40.Ha Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
84.60.Jt Photoelectric conversion
42.50.Ar Photon statistics and coherence theory

Lattice relaxation process and crystallographic tilt in GaP layers grown on misoriented Si(001) substrates by metalorganic vapor phase epitaxy

Yasufumi Takagi, Yuzo Furukawa, Akihiro Wakahara, and Hirofumi Kan

J. Appl. Phys. 107, 063506 (2010); http://dx.doi.org/10.1063/1.3310479 (8 pages) | Cited 13 times

Online Publication Date: 22 March 2010

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A lattice relaxation process and a crystallographic tilt in GaP layers grown on misoriented Si(001) substrates by metalorganic vapor phase epitaxy were investigated. Strained pseudomorphic GaP layers without defects on Si were successfully achieved by the optimization of growth conditions. Below critical thickness, the strained GaP layers were tilted in the misoriented direction of the Si substrates and triclinically distorted. Above critical thickness, the residual strain in the GaP layers was progressively relaxed with increased thickness of the GaP layers by forming 60° misfit dislocations propagating to the two orthogonal 〈110〉 directions at the heterointerface. X-ray diffuse scattering around the symmetrical GaP(004) diffraction was observed after introducing misfit dislocations. Diffuse scattering became dominant with an increase in the density of the misfit dislocations and resulted in a broadening of the full width at half maximum of the x-ray rocking curves. The GaP layers that were relaxed with highly dense misfit dislocations were tilted opposite of the misoriented direction due to the imbalance nucleation of the misfit dislocations on each {111} glide plane.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
78.70.Ck X-ray scattering
81.05.Ea III-V semiconductors

Phase stability of carbon clathrates at high pressure

Jian-Tao Wang, Changfeng Chen, Ding-Sheng Wang, H. Mizuseki, and Y. Kawazoe

J. Appl. Phys. 107, 063507 (2010); http://dx.doi.org/10.1063/1.3359682 (4 pages) | Cited 4 times

Online Publication Date: 22 March 2010

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Group-IV element clathrates have attracted considerable interest in recent years. Here, we report an ab initio study on the structural stability of carbon clathrates at high pressure and identify fcc-C136 clathrate as the third most stable carbon phase after cubic diamond and hexagonal graphite. A pressure-induced phase transition is predicted to occur around 17 GPa from hexagonal graphite to fcc-C136, which is more stable than other carbon clathrates such as hex-C40 and sc-C46, and the recently predicted metastable M-carbon up to 26 GPa. Phonon dispersion calculations confirm the dynamic stability of fcc-C136 as well as diamond.
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61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.66.Bi Elemental solids
64.70.K- Solid-solid transitions
64.60.My Metastable phases
62.50.-p High-pressure effects in solids and liquids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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