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20 Dec 2010

Volume 97, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 252101 (2010); http://dx.doi.org/10.1063/1.3525588 (3 pages)

Wei Pan, Stephen W. Howell, Anthony Joseph Ross, III, Taisuke Ohta, and Thomas A. Friedmann
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Passively harmonically mode-locked vertical-external-cavity surface-emitting laser emitting 1.1 ps pulses at 147 GHz repetition rate

A. H. Quarterman, A. Perevedentsev, K. G. Wilcox, V. Apostolopoulos, H. E. Beere, I. Farrer, D. A. Ritchie, and A. C. Tropper

Appl. Phys. Lett. 97, 251101 (2010); http://dx.doi.org/10.1063/1.3527973 (3 pages) | Cited 2 times

Online Publication Date: 20 December 2010

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Coupled-cavity passive harmonic mode-locking of a quantum well based vertical-external-cavity surface-emitting laser has been demonstrated, yielding an output pulse train of 1.5 ps pulses at a repetition rate of 80 GHz and with an average power of 80 mW. Harmonic mode-locking results from coupling between the main laser cavity and a cavity formed within the substrate of the saturable absorber structure. Mode-locking on the second harmonic of the substrate cavity allows a train of 1.1 ps pulses to be generated at a repetition rate of 147 GHz with 40 mW average power.
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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
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

High responsivity ultraviolet photodetector realized via a carrier-trapping process

J. S. Liu, C. X. Shan, B. H. Li, Z. Z. Zhang, C. L. Yang, D. Z. Shen, and X. W. Fan

Appl. Phys. Lett. 97, 251102 (2010); http://dx.doi.org/10.1063/1.3527974 (3 pages) | Cited 4 times

Online Publication Date: 20 December 2010

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Metal-semiconductor-metal structured ultraviolet (UV) photodetector has been fabricated from zinc oxide films. The responsivity of the photodetector can reach 26 000 A/W at 8 V bias, which is the highest value ever reported for a semiconductor ultraviolet photodetector. The origin of the high responsivity has been attributed to the carrier-trapping process occurred in the metal-semiconductor interface, which has been confirmed by the asymmetric barrier height at the two sides of the metal-semiconductor interdigital electrodes. The results reported in this paper provide a way to high responsivity UV photodetectors, which thus may address a step toward future applications of UV photodetectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Sx Metal-semiconductor-metal structures

Thermo-optic detection of terahertz radiation from a quantum cascade laser

A. van Kolck, M. Amanti, M. Fischer, M. Beck, J. Faist, and J. Lloyd-Hughes

Appl. Phys. Lett. 97, 251103 (2010); http://dx.doi.org/10.1063/1.3528456 (3 pages)

Online Publication Date: 20 December 2010

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We investigate the asynchronous detection of terahertz radiation from a quantum cascade laser using an electro-optic sampling apparatus. The signal does not vary substantially upon rotating the detection crystal, while a characteristic angle dependence is exhibited for synchronized time-domain pulses from a photoconductive emitter. Upon increasing the electrical modulation frequency of the cascade laser the unsynchronized signal decreases in good agreement with a thermal detector. Rather than being electro-optic in origin, we therefore ascribe the unsynchronized signal to a thermo-optic modulation of the refractive index. A simple model is in good agreement with the effect’s frequency dependence.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Highly temperature insensitive quantum cascade lasers

Y. Bai, N. Bandyopadhyay, S. Tsao, E. Selcuk, S. Slivken, and M. Razeghi

Appl. Phys. Lett. 97, 251104 (2010); http://dx.doi.org/10.1063/1.3529449 (3 pages) | Cited 8 times

Online Publication Date: 20 December 2010

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An InP based quantum cascade laser (QCL) heterostructure emitting around 5 μm is grown with gas-source molecular beam epitaxy. The QCL core design takes a shallow-well approach to maximize the characteristic temperatures, T0 and T1, for operations above room temperature. A T0 value of 383 K and a T1 value of 645 K are obtained within a temperature range of 298–373 K. In room temperature continuous wave operation, this design gives a single facet output power of 3 W and a wall plug efficiency of 16% from a device with a cavity length of 5 mm and a ridge width of 8 μm.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Color display using micromechanically coupled mirrors

Won Han and Young-Ho Cho

Appl. Phys. Lett. 97, 251105 (2010); http://dx.doi.org/10.1063/1.3529468 (3 pages)

Online Publication Date: 20 December 2010

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We present interferometric modulators, reproducing green, blue, and red colors using selective actuation of mechanically coupled mirror arrays having an identical air gap for simple fabrication process. The present interferometric modulators reproduce green, blue, and red colors at switching modes of (000), (010), and (101), where the spectrum peaks for the colors are measured at wavelengths of 511±5, 478±3, and 644±9 nm with maximum intensities of 77±5%, 73±2%, and 81±5%, respectively. Therefore, we experimentally demonstrated the color reproduction capability of the present interferometric modulators for display applications.
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42.79.Kr Display devices, liquid-crystal devices
42.79.Hp Optical processors, correlators, and modulators
07.60.Ly Interferometers

Time-resolved amplified spontaneous emission in quantum dots

J. Gomis-Bresco, S. Dommers-Völkel, O. Schöps, Y. Kaptan, O. Dyatlova, D. Bimberg, and U. Woggon

Appl. Phys. Lett. 97, 251106 (2010); http://dx.doi.org/10.1063/1.3529447 (3 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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In time-resolved experiments at InGaAs/GaAs quantum-dots-in-a-well (DWELL) semiconductor optical amplifiers, pump-probe of the ground state (GS) population, and complementary measurement of the amplified spontaneous emission of the excited state (ES) population, we are able to separate the early subpicosecond dephasing dynamics from the later picosecond population relaxation dynamics. We observe a 10 ps delay between the nonlinear GS pulse amplification and the subsequent ES population drop-off that supports the dominance of a direct two dimensional reservoir-GS capture relaxation path in electrically pumped quantum-dot-DWELL structures.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Lm Parametric down conversion and production of entangled photons

Tunnel injection In0.25Ga0.75N/GaN quantum dot light-emitting diodes

Pallab Bhattacharya, Meng Zhang, and John Hinckley

Appl. Phys. Lett. 97, 251107 (2010); http://dx.doi.org/10.1063/1.3527935 (3 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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Hole tunnel injection is incorporated in the design of In0.25Ga0.75N/GaN quantum dot light-emitting diodes with peak emission at λ ∼ 500 nm. Calculations show that cold holes are uniformly injected into all five quantum dot layers in the active region. Measurements were made on devices having different thicknesses, teff, of the In0.43Al0.57N hole tunnel barrier. The best performance is exhibited by a device with teff = 1.5 nm. The maximum external quantum efficiency is 0.66% at 220 A/cm2, and an efficiency droop of 20% at 360 A/cm2 is tentatively attributed to reduced Auger recombination and leakage of hot carriers.
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85.60.Jb Light-emitting devices

Emission of cylindrical and elliptical vector beams from radial Bragg Lasers

Ori Weiss and Jacob Scheuer

Appl. Phys. Lett. 97, 251108 (2010); http://dx.doi.org/10.1063/1.3529462 (3 pages)

Online Publication Date: 21 December 2010

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Radially and azimuthally polarized beams are shown to be naturally emitted from radial Bragg lasers depending on the supported polarization in the cavity (TE or TM). The impact of structure imperfection and deviation from a circular shape on the lasing properties is investigated, showing a red-shift in the resonance frequency, and a modification of the radial/azimuthal polarization profile forming elliptical vector beams. The comparison of the analysis to the experimental results indicates that the fabricated lasers are not perfectly circular with ellipticity in the order of 1%.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.25.Ja Polarization

High slope efficiency liquid crystal lasers

Carrie Mowatt, Stephen M. Morris, Timothy D. Wilkinson, and Harry J. Coles

Appl. Phys. Lett. 97, 251109 (2010); http://dx.doi.org/10.1063/1.3526750 (3 pages)

Online Publication Date: 21 December 2010

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In this letter, we demonstrate high slope efficiency laser emission from reflective liquid crystal laser devices with a silicon backplane. Three different cell architectures were fabricated and each resulting laser device was then characterized in terms of the excitation threshold and the slope efficiency when optically excited close to the absorption maximum of the gain medium (pyrromethene 597). By combining a high gain medium with double-pass geometry, as well as the optimum cell thickness, the results demonstrate that it is possible to reduce thresholds by 25% and achieve slope efficiencies as high as 60%.
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42.55.Mv Dye lasers
42.70.Hj Laser materials
42.60.By Design of specific laser systems

Current crowding effect on the ideality factor and efficiency droop in blue lateral InGaN/GaN light emitting diodes

V. K. Malyutenko, S. S. Bolgov, and A. D. Podoltsev

Appl. Phys. Lett. 97, 251110 (2010); http://dx.doi.org/10.1063/1.3529470 (3 pages) | Cited 2 times

Online Publication Date: 21 December 2010

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By examining two types of lateral InGaN/GaN light emitting diodes with different contact patterns, we demonstrate that in the intermediate range of current where the space-charge region dominates in the device performance, the ideality factor (β) increases from 1.9 (current spreading design) up to 2.4 (current crowding design). This modification of β-factor could be erroneously treated as the change of free carrier recombination nature. The current crowding design is also responsible for the local overheating and heavier efficiency droop that occurs at the characteristic current 2.3 times smaller in comparison with the current spreading design.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling

Direct observation of iso-frequency contour of surface modes in defective photonic crystals in real space

Lei Shi, Haiwei Yin, Xiaolong Zhu, Xiaohan Liu, and Jian Zi

Appl. Phys. Lett. 97, 251111 (2010); http://dx.doi.org/10.1063/1.3524520 (3 pages)

Online Publication Date: 22 December 2010

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Direct observation of iso-frequency contours of surface modes in defective photonic crystals in real space is demonstrated in a hybrid photonic and plasmonic crystals structure with inevitable defects. The scattering process of by the randomly dispersed defects in periodic structure is analytically discussed and used to explain the reason why defects can induce direct observation of iso-frequency contour in real space. The band-structures are also obtained from the observed iso-frequency contours. The findings in this work can be useful to comprehensively characterize photonic crystals.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.70.Qs Photonic bandgap materials
78.68.+m Optical properties of surfaces

GaN-based surface-emitting laser with two-dimensional photonic crystal acting as distributed-feedback grating and optical cladding

Shoichi Kawashima, Takeshi Kawashima, Yasuhiro Nagatomo, Yuichiro Hori, Hideo Iwase, Takeshi Uchida, Katsuyuki Hoshino, Aihiko Numata, and Mamoru Uchida

Appl. Phys. Lett. 97, 251112 (2010); http://dx.doi.org/10.1063/1.3528352 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2010

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We demonstrate GaN-based distributed-feedback surface-emitting lasers grown on sapphire substrates with a two-dimensional (2D) square-lattice photonic crystal (PhC) that forms a high-aspect-ratio void array (void diameter: 65 nm and depth: 220 nm). The 2D PhC layer acts as both distributed-feedback grating and p-type optical cladding of a separate confinement heterostructure. To form the 2D PhC in the nitride semiconductor layers, we developed an embedding process that uses mass-transport phenomena. Crystallographic facets appeared on the inner walls of the embedded voids. Room-temperature lasing action was observed at 406.0 nm for a PhC lattice constant of 162.5 nm. The threshold current density was 9.7 kA/cm2 for a 120-μm-square p-contact electrode.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Tv Photonic crystal lasers and coherent effects

A type-II superlattice period with a modified InAs to GaSb thickness ratio for midwavelength infrared photodiode performance improvement

J. B. Rodriguez, C. Cervera, and P. Christol

Appl. Phys. Lett. 97, 251113 (2010); http://dx.doi.org/10.1063/1.3529940 (3 pages) | Cited 3 times

Online Publication Date: 23 December 2010

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We present a type-II superlattice period with a modified InAs to GaSb thickness ratio for midinfrared detection. In this kind of structure, the large electron-hole wave-function overlap and the low intrinsic carrier concentration lead to a significant signal-to-noise ratio enhancement. For the proof of concept, a sample designed with an InAs to GaSb thickness ratio close to 2 was grown. Comparison with standard design photodiodes shows an improvement of the differential resistance area product by one and a half decade while the quantum efficiency was more than doubled.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Characteristics of efficiency droop in GaN-based light emitting diodes with an insertion layer between the multiple quantum wells and n-GaN layer

S. P. Chang, C. H. Wang, C. H. Chiu, J. C. Li, Y. S. Lu, Z. Y. Li, H. C. Yang, H. C. Kuo, T. C. Lu, and S. C. Wang

Appl. Phys. Lett. 97, 251114 (2010); http://dx.doi.org/10.1063/1.3531957 (3 pages) | Cited 1 time

Online Publication Date: 23 December 2010

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We have studied the characteristics of efficiency droop in GaN-based light emitting diodes (LEDs) with different kinds of insertion layers (ILs) between the multiple quantum wells (MQWs) layer and n-GaN layer. By using low-temperature (LT) (780 °C) n-GaN as IL, the efficiency droop behavior can be alleviated from 54% in reference LED to 36% from the maximum value at low injection current to 200 mA, which is much smaller than that of 49% in LED with InGaN/GaN short-period superlattices layer. The polarization field in MQWs is found to be smallest in LED with InGaN/GaN SPS layer. However, the V-shape defect density, about 5.3×108 cm−2, in its MQWs region is much higher than that value of 2.9×108 cm−2 in LED with LT n-GaN layer, which will lead to higher defect-related tunneling leakage of carriers. Therefore, we can mainly assign this alleviation of efficiency droop to the reduction of dislocation density in MQWs region rather than the decrease of polarization field.
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85.60.Jb Light-emitting devices

Electrically pumped ultraviolet random lasing from ZnO films: Compensation between optical gain and light scattering

Ye Tian, Xiangyang Ma, Lu Jin, and Deren Yang

Appl. Phys. Lett. 97, 251115 (2010); http://dx.doi.org/10.1063/1.3531960 (3 pages)

Online Publication Date: 23 December 2010

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We have demonstrated the compensation between optical gain and light scattering in electrically pumped random lasing (RL) from ZnO films through investigating the electroluminescence of MgxZn1−xO/ZnO (x = 0.25 and 1) heterostructured devices. As the active ZnO films are sol-gel derived, both heterostructured devices can be electrically pumped into RL at appropriate forward currents. While the active ZnO films are prepared by sputtering, only the MgO/ZnO heterostructured devices can generate RL pumped with sufficient forward currents. It is believed that the light scattering in the sputtered ZnO films is weaker than that in the sol-gel derived ones. However, the inferior light scattering capability of the sputtered ZnO films can be compensated by the MgO/ZnO-heterostructure-enabled higher optical gain in the electrically pumped RL.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.25.Fx Diffraction and scattering
78.60.Fi Electroluminescence
68.55.-a Thin film structure and morphology

Real-time single-shot three-dimensional and contrast-enhanced optical coherence imaging using phase coherent photorefractive quantum wells

A. Kabir, A. Dongol, X. Wang, and H. P. Wagner

Appl. Phys. Lett. 97, 251116 (2010); http://dx.doi.org/10.1063/1.3531589 (3 pages)

Online Publication Date: 23 December 2010

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We demonstrate two real-time optical coherence imaging acquisition modes using all-optical phase coherent photorefractive ZnSe quantum wells as dynamic holographic films. These films use the coherence of excitons for time-gating which provides depth information of an object according to the brightness profile of its holographic image. This quality allows depth-resolved imaging of moving particles with a resolution of a few micrometers in a single-shot three-dimensional mode. In a complementary contrast-enhanced mode moving particles are imaged by the local enhancement of a static reference hologram, enabling optical coherence imaging at a large depth-of-field.
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42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics
42.40.Eq Holographic optical elements; holographic gratings
42.30.Wb Image reconstruction; tomography
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Wc Optical coatings
42.30.Va Image forming and processing

Direct minority carrier lifetime measurements and recombination mechanisms in long-wave infrared type II superlattices using time-resolved photoluminescence

Blair C. Connelly, Grace D. Metcalfe, Hongen Shen, and Michael Wraback

Appl. Phys. Lett. 97, 251117 (2010); http://dx.doi.org/10.1063/1.3529458 (3 pages) | Cited 4 times

Online Publication Date: 23 December 2010

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We present a direct optical measurement of minority carrier lifetime as a function of temperature and excitation density in long-wave infrared InAs/GaSb type II superlattices using time-resolved photoluminescence. Results indicate that carrier lifetime is dominated by Shockley–Read–Hall recombination, with a lifetime of 30 ns at 77 K. Below 40 K, we observe a freeze-out of carriers and increased contributions from radiative recombination. High-injection measurements yield a radiative recombination coefficient of 1.8×10−10 cm3/s and an upper limit of the Auger recombination coefficient of 10−28 cm6/s at 60 K. An acceptor level of ∼ 20 meV above the valence band is also determined.
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81.05.Ea III-V semiconductors
73.21.Cd Superlattices
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
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rf mode switching in a relativistic magnetron with diffraction output

Meiqin Liu, Cedric Michel, Sarita Prasad, Mikhail I. Fuks, Edl Schamiloglu, and Chun-Liang Liu

Appl. Phys. Lett. 97, 251501 (2010); http://dx.doi.org/10.1063/1.3529463 (3 pages) | Cited 5 times

Online Publication Date: 22 December 2010

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The relativistic magnetron with diffraction output (RMDO) has demonstrated nearly 70% efficiency in recent simulations. This letter reports a rapid mode switching technique in the RMDO using a low power, short-pulse, external single frequency signal. The MAGIC electromagnetic finite-difference-time-domain particle-in-cell code used in simulations demonstrated that an input signal of 300 kW is sufficient to switch neighboring modes in a gigawatt output power A6 RMDO with a transparent cathode, whereas for the original A6 magnetron configuration with radial extraction driven by a transparent cathode 30 MW is required. This frequency agility adds additional versatility to this high power microwave source.
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52.80.Pi High-frequency and RF discharges
52.65.Rr Particle-in-cell method
52.75.Kq Plasma switches (e.g., spark gaps)
52.27.Ny Relativistic plasmas
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
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Scanning transmission electron microscopy investigation of the Si(111)/AlN interface grown by metalorganic vapor phase epitaxy

G. Radtke, M. Couillard, G. A. Botton, D. Zhu, and C. J. Humphreys

Appl. Phys. Lett. 97, 251901 (2010); http://dx.doi.org/10.1063/1.3527928 (3 pages) | Cited 2 times

Online Publication Date: 20 December 2010

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The structure and chemistry of the interface between a Si(111) substrate and an AlN(0001) thin film grown by metalorganic vapor phase epitaxy have been investigated at a subnanometer scale using high-angle annular dark field imaging and electron energy-loss spectroscopy. 〈11math0〉AlN∥〈110〉Si and 〈0001〉AlN∥〈111〉Si epitaxial relations were observed and an Al-face polarity of the AlN thin film was determined. Despite the use of Al deposition on the Si surface prior to the growth, an amorphous interlayer of composition SiNx was identified at the interface. Mechanisms leading to its formation are discussed.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
79.20.Uv Electron energy loss spectroscopy
68.35.Ct Interface structure and roughness

The atomic structure and polarization of strained SrTiO3/Si

D. P. Kumah, J. W. Reiner, Y. Segal, A. M. Kolpak, Z. Zhang, D. Su, Y. Zhu, M. S. Sawicki, C. C. Broadbridge, C. H. Ahn, and F. J. Walker

Appl. Phys. Lett. 97, 251902 (2010); http://dx.doi.org/10.1063/1.3529460 (3 pages) | Cited 1 time

Online Publication Date: 20 December 2010

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For thin film devices based on coupling ferroelectric polarization to charge carriers in semiconductors, the role of the interface is critical. To elucidate this role, we use synchrotron x-ray diffraction to determine the interface structure of epitaxial SrTiO3 grown on the (001) surface of Si. The average displacement of the O octahedral sublattice relative to the Sr sublattice determines the film polarization and is measured to be about 0.05 nm toward the Si, with Ti off-center displacements 0.009 nm away from the substrate. Measurements of films with different boundary conditions on the top of the SrTiO3 show that the polarization at the SrTiO3/Si interface is dominated by oxide-Si chemical interactions.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.84.Cg PZT ceramics and other titanates
77.55.hn Other piezoelectric or electrostrictive films
77.22.Ej Polarization and depolarization
68.35.Ct Interface structure and roughness
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Diamond as a high pressure gauge up to 2.7 Mbar

Natalia Dubrovinskaia, Leonid Dubrovinsky, Razvan Caracas, and Michael Hanfland

Appl. Phys. Lett. 97, 251903 (2010); http://dx.doi.org/10.1063/1.3529454 (3 pages) | Cited 2 times

Online Publication Date: 21 December 2010

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A pressure gauge is a key issue of any high pressure experiment in a diamond anvil cell (DAC). Here we present a method of in situ synthesis of microcrystals of diamond that can be further used as a pressure standard in the course of the same DAC experiment. Calibration curve of the Raman shift versus pressure is extended up to 270 GPa and experimental results are compared with those of ab initio calculations.
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07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
07.07.Mp Transducers
06.20.fb Standards and calibration

Direct acoustic phonon excitation by intense and ultrashort terahertz pulses

J.-M. Manceau, P. A. Loukakos, and S. Tzortzakis

Appl. Phys. Lett. 97, 251904 (2010); http://dx.doi.org/10.1063/1.3529466 (3 pages)

Online Publication Date: 21 December 2010

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We report on the direct and resonant excitation of acoustic phonons in an AlGaAs intrinsic semiconductor using intense coherent and single cycle terahertz pulses created by two-color femtosecond laser pulse filamentation in air. While the electrons are left unperturbed, we follow the lattice dynamics with time-delayed optical photons tuned to the interband transition.
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81.05.Ea III-V semiconductors
62.65.+k Acoustical properties of solids
63.20.dd Measurements
78.70.Gq Microwave and radio-frequency interactions
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Metal-organic frameworks as promising candidates for future ultralow-k dielectrics

K. Zagorodniy, G. Seifert, and H. Hermann

Appl. Phys. Lett. 97, 251905 (2010); http://dx.doi.org/10.1063/1.3529461 (2 pages)

Online Publication Date: 21 December 2010

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A class of Zn4O(CO2)6-based metal-organic frameworks (MOFs) is theoretically analyzed with respect to suitability as an interlayer dielectric material for applications in semiconducting devices. The static dielectric constant is calculated using the Clausius–Mossotti approach. For 3 of about 30 of the considered MOFs excellent combinations of ultralow dielectric constant, elastic bulk modulus, and gap energy are found favoring these materials as outstanding candidates for future ultralow-k dielectric materials.
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81.05.Zx New materials: theory, design, and fabrication
77.22.Ch Permittivity (dielectric function)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
71.20.Rv Polymers and organic compounds

Piezoelectric characteristic of nanocrystalline AlN films obtained by pulsed laser deposition at room temperature

C. Cibert, P. Dutheil, C. Champeaux, O. Masson, G. Trolliard, F. Tétard, and A. Catherinot

Appl. Phys. Lett. 97, 251906 (2010); http://dx.doi.org/10.1063/1.3527924 (3 pages)

Online Publication Date: 21 December 2010

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Aluminum nitride (AlN) thin films were deposited at room temperature by pulsed laser deposition, and their nanostructure and piezoelectric properties were investigated as a function of fluence. For all fluences, the films were found to consist of an amorphous AlN matrix containing crystalline AlN nanoparticles with size of 6–7 nm. These nanoparticles spark off the good piezoelectric response, with d33 piezoelectric coefficients between 2.3 and 3.8 pm V−1, similar to those obtained for (002)-oriented AlN films deposited at higher temperatures. These results indicate that nanocrystalline AlN films deposited at room temperature are good candidates for integration in acoustic wave applications.
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81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
68.55.ag Semiconductors
77.55.hd AlN
77.65.Bn Piezoelectric and electrostrictive constants
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

In vacancies in InN grown by plasma-assisted molecular beam epitaxy

Floris Reurings, Filip Tuomisto, Chad S. Gallinat, Gregor Koblmüller, and James S. Speck

Appl. Phys. Lett. 97, 251907 (2010); http://dx.doi.org/10.1063/1.3516467 (3 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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The authors have applied positron annihilation spectroscopy to study the effect of different growth conditions on vacancy formation in In- and N-polar InN grown by plasma-assisted molecular beam epitaxy. The results suggest that the structural quality of the material and limited diffusion of surface adatoms during growth dictate the In vacancy formation in low electron-density undoped epitaxial InN, while growth conditions and thermodynamics have a less important role, contrary to what is observed in, e.g., GaN. Furthermore, the results imply that in high quality InN, the electron mobility is likely limited not by ionized point defect scattering, but rather by threading dislocations.
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61.72.jd Vacancies
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.70.Bj Positron annihilation
66.30.H- Self-diffusion and ionic conduction in nonmetals
72.20.Fr Low-field transport and mobility; piezoresistance
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
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