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23 Jan 2012

Volume 100, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 041101 (2012); http://dx.doi.org/10.1063/1.3675885 (4 pages)

Seung Ho Choi and Young L. Kim
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Random lasing mode alterations by single-nanoparticle perturbations

Seung Ho Choi and Young L. Kim

Appl. Phys. Lett. 100, 041101 (2012); http://dx.doi.org/10.1063/1.3675885 (4 pages) | Cited 2 times

Online Publication Date: 23 January 2012

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We numerically demonstrate that alterations in random lasing modes can serve as a highly sensitive biosensing mechanism for single-nanoparticle quantitation. In our approach, subtle perturbations from a single nanoparticle can induce dramatic changes in multiple eigenmodes in disordered structures that can be detected by spectral variations of lasing emission peaks. Several resonance mode frequencies show relatively linear spectral responses to nanoscale perturbations, and each mode possess different levels of perturbation sensitivity. We also show that such behavior exists in both highly and loosely packed disordered media. We envision that the simplicity of such realization will facilitate the biosensor development using random lasers.
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42.55.Zz Random lasers

Spectrally resolved size-dependent third-order nonlinear optical properties of colloidal CdSe quantum dots

M. Nyk, D. Wawrzynczyk, J. Szeremeta, and M. Samoc

Appl. Phys. Lett. 100, 041102 (2012); http://dx.doi.org/10.1063/1.3679381 (4 pages) | Cited 4 times

Online Publication Date: 23 January 2012

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Nonlinear absorption and nonlinear refraction of colloidal CdSe quantum dots (QDs) of two sizes were investigated in a wide spectral range with the Z-scan technique using a tunable femtosecond laser system. The nonlinear absorption was found to be the strongest close to twice the wavelength of the second exciton absorption band of the QDs. Based on nonlinear optical parameters the exciton binding energy has been determined. The current results are compared to the nonlinear properties of CdSe QDs presented in the literature. The features of this system relevant for multiphoton fluorescence microscopy applications are discussed.
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78.67.Hc Quantum dots
82.70.Dd Colloids
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Vertically coupled photonic molecule laser

Xin Tu, Yi-Kuei Wu, and L. Jay Guo

Appl. Phys. Lett. 100, 041103 (2012); http://dx.doi.org/10.1063/1.3678191 (4 pages) | Cited 1 time

Online Publication Date: 23 January 2012

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A photonic molecule semiconductor microdisk laser consisting of three vertically coupled disks of 1.4 μm in diameter is fabricated and optically pumped. Clear mode splitting arising from the strong vertical optical coupling is observed and confirmed by the coupled mode theory. The inter-coupling strength ∼0.40 THz of optical modes between adjacent disks is calculated and agrees well with the experiment. Moreover the multiple stacked microdisk laser has a large spontaneous emission factor (β ∼ 0.72) by fitting the L-L curves and provides some potential functional devices in cavity quantum electrodynamics systems and highly-dense photonic integrated circuits.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.-m Integrated optics

In-line high efficient fiber polarizer based on surface plasmon

Chun-Hua Dong, Chang-Ling Zou, Xi-Feng Ren, Guang-Can Guo, and Fang-Wen Sun

Appl. Phys. Lett. 100, 041104 (2012); http://dx.doi.org/10.1063/1.3678591 (4 pages) | Cited 3 times

Online Publication Date: 23 January 2012

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An in-line high efficient polarizer, composed of tapered fiber on the Au thin film, is theoretically proposed and experimentally demonstrated. The protocol is based on the high efficient adiabatic conversion of transverse magnetic mode from tapered fiber into surface plasmon (SP) and attenuates quickly in metal film. On the contrary, the transverse electric polarized light is influenced hardly in the whole process. The polarization extinction ratio higher than 500:1 (≈27 dB) is obtained in our experiment. Our demonstration offers a potential way to manipulate the polarization of light in integrated circuit and may inspirit more attention to surface plasmon based devices for polarization controlling.
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42.81.Gs Birefringence, polarization
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Ci Filters, zone plates, and polarizers

Investigation of possible microcavity effect on lasing threshold of nonradiative-scattering-dominated semiconductor lasers

Sushil Kumar and Qing Hu

Appl. Phys. Lett. 100, 041105 (2012); http://dx.doi.org/10.1063/1.3678595 (4 pages)

Online Publication Date: 23 January 2012

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The effect of enhanced rate of spontaneous emission on gain and lasing threshold of semiconductor microcavity lasers has not been discussed clearly. Some reports have suggested that the lasing threshold in microcavities could possibly be lowered due to the so-called Purcell effect. Here, we argue that gain in weakly coupled semiconductor cavities is a local phenomenon, which occurs due to stimulated emission induced by an electromagnetic excitation and remains unaffected by the cavity boundary conditions. Hence, the Purcell effect in microcavities filled uniformly with a gain medium should not lead to a reduction in the laser’s threshold pump density, provided radiative scattering is not the dominant relaxation mechanism in the excited state. A systematic experimental investigation of laser threshold in parallel-plate semiconductor microcavity terahertz quantum-cascade lasers of different dimensions was found to be in accordance with our arguments.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers

Ultraviolet and infrared femtosecond laser induced periodic surface structures on thin polymer films

Esther Rebollar, Javier R. Vázquez de Aldana, José A. Pérez-Hernández, Tiberio A. Ezquerra, Pablo Moreno, and Marta Castillejo

Appl. Phys. Lett. 100, 041106 (2012); http://dx.doi.org/10.1063/1.3679103 (4 pages) | Cited 3 times

Online Publication Date: 24 January 2012

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This work demonstrates the formation of femtosecond laser induced periodic surface structures (LIPSS) by multipulse irradiation with the fundamental and 3rd harmonic of a linearly polarized Ti:sapphire laser (795 and 265 nm) on thin films of the polymers poly (ethylene terephthalate), poly (trimethylene terephthalate), and poly (carbonate bisphenol A) prepared by spin-coating. LIPSS, inspected by atomic force microscopy, are formed upon multiple pulse UV and IR irradiation with wavelength-sized period in a narrow range of fluences below the ablation threshold. Control and tunability of the size and morphology of the periodic structures become thus possible ensuring photochemical integrity of polymer films.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.50.-m Photochemistry
68.55.J- Morphology of films
52.38.Mf Laser ablation
61.41.+e Polymers, elastomers, and plastics

Using circular Dammann gratings to produce impulse optic vortex rings

Yuchao Zhang, Nan Gao, and Changqing Xie

Appl. Phys. Lett. 100, 041107 (2012); http://dx.doi.org/10.1063/1.3679111 (4 pages) | Cited 2 times

Online Publication Date: 24 January 2012

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Combining the circular Dammann grating and vortex phase structures, we present circular Dammann vortex gratings (CDVGs) for the generation of impulse vortex rings in the far field. Theoretical results reveal that each diffraction order is mainly composed of a single topological charged vortex beam. Numerical solution and fabrication method, as well as the experimental results are given. Our results suggest that CDVGs can provide a relatively simple approach to produce impulse optics vortex rings for many potential applications.
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42.79.Dj Gratings
42.25.-p Wave optics

Confined one-way mode at magnetic domain wall for broadband high-efficiency one-way waveguide, splitter and bender

Xiaogang Zhang, Wei Li, and Xunya Jiang

Appl. Phys. Lett. 100, 041108 (2012); http://dx.doi.org/10.1063/1.3679172 (4 pages) | Cited 1 time

Online Publication Date: 24 January 2012

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We find the one-way mode (OWM) can be well-confined at the magnetic domain wall by the photonic bandgap of gyromagnetic bulk material. Utilizing the well-confined one-way mode at the domain wall, we demonstrate the photonic one-way waveguide, splitter and bender can be realized with simple structures, which are predicted to be high-efficiency, broadband, frequency-independent, reflection-free, crosstalk-proof, and robustness against disorder. Additionally, we find that the splitter and bender in our proposal can be transformed into each other with magnetic control, which may have great potential applications in all photonic integrated circuit.
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42.82.-m Integrated optics
42.70.Qs Photonic bandgap materials

Type-II InP-based lasers emitting at 2.55 μm

Stephan Sprengel, Alexander Andrejew, Kristijonas Vizbaras, Tobias Gruendl, Kathrin Geiger, Gerhard Boehm, Christian Grasse, and Markus-Christian Amann

Appl. Phys. Lett. 100, 041109 (2012); http://dx.doi.org/10.1063/1.3679378 (3 pages) | Cited 5 times

Online Publication Date: 25 January 2012

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Room-temperature lasing at 2.55 μm is reported for InP-based GaInAs/GaAsSb type-II quantum well lasers in pulsed mode up to 42 °C. This record long-wavelength lasing has become feasible by implementing compressive strain in both materials and a carrier confinement design using an AlAsSb/AlGaInAs electron/hole blocking layer. The device concept appears promising for extending the wavelength range further towards 3 μm.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Measurements and imaging of optical gain in optically pumped alkali-rare gas systems

Kristin L. Galbally-Kinney, Daniel L. Maser, William J. Kessler, Wilson T. Rawlins, and Steven J. Davis

Appl. Phys. Lett. 100, 041110 (2012); http://dx.doi.org/10.1063/1.3679613 (3 pages)

Online Publication Date: 25 January 2012

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We have applied diode laser gain spectroscopy to quantitative spectral measurements and 2-D images of small-signal gain in optically pumped cesium-rare gas mixtures. Results are illustrated for Cs absorption broadened by Kr, with C2H6 added to induce spin-orbit mixing between the upper states (2P1/2 and 2P3/2) of the two transitions. The imaging technique provides spatial information relevant to the beam quality of the alkali laser output. Spectral and spatial gain measurements of this type are applicable to investigations of power scaling in advanced diode-pumped alkali laser systems, for both the spin-orbit mixed and exciplex-assisted configurations.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Frequency locking of single-mode 3.5-THz quantum cascade lasers using a gas cell

Y. Ren, J. N. Hovenier, M. Cui, D. J. Hayton, J. R. Gao, T. M. Klapwijk, S. C. Shi, T.-Y. Kao, Q. Hu, and J. L. Reno

Appl. Phys. Lett. 100, 041111 (2012); http://dx.doi.org/10.1063/1.3679620 (4 pages) | Cited 4 times

Online Publication Date: 25 January 2012

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We report frequency locking of two 3.5-THz third-order distributed feedback (DFB) quantum cascade lasers (QCLs) by using methanol molecular absorption lines, a proportional-integral-derivative controller, and a NbN bolometer. We show that the free-running linewidths of the QCLs are dependent on the electrical and temperature tuning coefficients. For both lasers, the frequency locking induces a similar linewidth reduction factor, whereby the narrowest locked linewidth is below 18 kHz with a Gaussian-like shape. The linewidth reduction factor and the ultimate linewidth correspond to the measured frequency noise power spectral density.
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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
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Parabolic tapered photonic crystal cavity in silicon

Boris Desiatov, Ilya Goykhman, and Uriel Levy

Appl. Phys. Lett. 100, 041112 (2012); http://dx.doi.org/10.1063/1.3679659 (3 pages) | Cited 3 times

Online Publication Date: 25 January 2012

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We demonstrate the design, fabrication, transmission spectrum measurement, and near-field characterization of a parabolic tapered one-dimensional photonic crystal cavity in silicon. The results shows a relatively high quality factor (∼43 000), together with a small modal volume of ∼1.1(λ/n)3. Moreover, the design allows repeatable device fabrication, as evident by the similar characteristics obtained for several tens of devices that were fabricated and tested. These demonstrated 1D PhC cavities may be used as a building block in integrated photonic circuits for optical on-chip interconnects and sensing applications.
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42.70.Qs Photonic bandgap materials
42.86.+b Optical workshop techniques
42.87.-d Optical testing techniques
07.79.Fc Near-field scanning optical microscopes
42.15.Eq Optical system design

Enhanced longitudinal mode spacing in blue-violet InGaN semiconductor lasers

I. V. Smetanin and P. P. Vasil’ev

Appl. Phys. Lett. 100, 041113 (2012); http://dx.doi.org/10.1063/1.3679376 (3 pages) | Cited 1 time

Online Publication Date: 26 January 2012

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An explanation of observed enhanced longitudinal mode spacing in InGaN semiconductor lasers has been proposed. It has been demonstrated that e-h plasma oscillations, which can exist in the laser active layer at certain driving conditions, are responsible for mode clustering effect. The resonant excitation of the plasma oscillations occurs due to longitudinal mode beating. The separation of mode clusters is typically by an order of magnitude larger that the individual mode spacing.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Time-dynamics of the two-color emission from vertical-external-cavity surface-emitting lasers

A. Chernikov, M. Wichmann, M. K. Shakfa, M. Scheller, J. V. Moloney, S. W. Koch, and M. Koch

Appl. Phys. Lett. 100, 041114 (2012); http://dx.doi.org/10.1063/1.3679607 (4 pages)

Online Publication Date: 26 January 2012

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The temporal stability of a two-color vertical-external-cavity surface-emitting laser is studied using single-shot streak-camera measurements. The collected data is evaluated via quantitative statistical analysis schemes. Dynamically stable and unstable regions for the two-color operation are identified and the dependence on the pump conditions is analyzed.
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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

Transition of beam dynamics in waveguide arrays with commensurate Stark ladders

G. Wang

Appl. Phys. Lett. 100, 041115 (2012); http://dx.doi.org/10.1063/1.3679640 (3 pages)

Online Publication Date: 26 January 2012

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We theoretically investigate the transition of coherent dynamics of light among different transport regimes in waveguide arrays with commensurate Stark ladders. Applying a transverse confinement to the lattice structure, the eigenvalue spectrum becomes discrete and equidistant, i.e., commensurate Stark ladders. Propagation of light undergoes a crossover from Bloch oscillations to harmonic oscillations, and one class of dynamics named hybrid oscillations appears. The transition is attributed to the localization-delocalization transition of ladders’ properties. Our results offer an extra degree of freedom to manipulate light.
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42.65.Wi Nonlinear waveguides
42.50.Ar Photon statistics and coherence theory
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Surface plasmon resonance and surface-enhanced Raman scattering sensing enabled by digital versatile discs

Xuan Dou, Pei-Yu Chung, Peng Jiang, and Jianli Dai

Appl. Phys. Lett. 100, 041116 (2012); http://dx.doi.org/10.1063/1.3679682 (4 pages) | Cited 2 times

Online Publication Date: 26 January 2012

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We report the simultaneous achievement of sensitive surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS) sensing using digital versatile discs (DVDs). The aluminum-covered data tracks of DVDs can efficiently concentrate local electromagnetic field, resulting in an excellent SPR medium (with sensitivity of ∼850 nm per refractive index unit which is higher than that of most available nanofabricated plasmonic substrates) with a small but measurable SERS enhancement. The SPR sensitivity and the optical spectra, as well as the distribution of electric field amplitude, are simulated using a finite-difference time-domain model. The theoretical predictions agree reasonably well with the experimental results.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet
02.70.Bf Finite-difference methods

n-ZnO:N/p-Si nanowire photodiode prepared by atomic layer deposition

Hyemin Kang, Jusang Park, Taejin Choi, Hanearl Jung, Kwang H. Lee, Seongil Im, and Hyungjun Kim

Appl. Phys. Lett. 100, 041117 (2012); http://dx.doi.org/10.1063/1.3679078 (4 pages) | Cited 5 times

Online Publication Date: 27 January 2012

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Core-shell p-n junction diode was fabricated using the atomic layer deposition (ALD) of ZnO on p-Si nanowire (NW) array prepared by electroless etching method. I-V measurements have shown that the carrier concentrations in ALD ZnO for both of the core-shell and planar diodes are effectively controlled by nitrogen doping to a proper level to form rectifying junction. Responsivity of the core-shell device was about 0.98 A/W at 660 nm, which is significantly improved compared to planar device. The superior sensitivity of core-shell structure is attributed to the effective carrier separation and collection originating from the characteristic of core-shell NWs full depletion.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.07.Gf Nanowires
85.30.Kk Junction diodes

Ultra-broad spontaneous emission and modal gain spectrum from a hybrid quantum well/quantum dot laser structure

S. M. Chen (陈思铭), K. J. Zhou (周可嘉), Z. Y. Zhang (张子旸), D. T. D. Childs, M. Hugues, A. J. Ramsay, and R. A. Hogg

Appl. Phys. Lett. 100, 041118 (2012); http://dx.doi.org/10.1063/1.3679178 (3 pages) | Cited 4 times

Online Publication Date: 27 January 2012

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We propose and demonstrate a hybrid quantum well/quantum dot structure to enhance the gain and spontaneous emission bandwidth of a quantum dot active region. A single quantum well is introduced into a multi-layer stack of quantum dots, spectrally positioned to cancel the losses due to the second excited state of the dots. As a result, the modal gain at room temperature is extended to 300 nm, covering the wavelength range of 1100-1400 nm, and spontaneous emission has a 250 nm, 3 dB linewidth from 1080-1335 nm, of interest to short-haul telecom and optical coherence tomography applications.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
FREE

Effect of an electron blocking layer on the piezoelectric field in InGaN/GaN multiple quantum well light-emitting diodes

Dong-Yul Lee, Sang-Heon Han, Dong-Ju Lee, Jeong Wook Lee, Dong-Joon Kim, Young Sun Kim, and Sung-Tae Kim

Appl. Phys. Lett. 100, 041119 (2012); http://dx.doi.org/10.1063/1.3681162 (4 pages)

Online Publication Date: 27 January 2012

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We report the effect of an electron blocking layer (EBL) on the piezoelectric field in InGaN/GaN multiple quantum well light-emitting diodes (LEDs). Electric-field-dependent ER measurements showed an enhanced piezoelectric field in LEDs with a p-AlGaN EBL compared with LEDs without EBL. In contrast, LEDs with a p-AlGaN EBL exhibited reduced blueshift and a sublinear increase of full width at half maximum in EL spectra at low current densities. These behaviors can be explained by the strong localization of injected carriers in dominant InGaN regions due to an increase of the piezoelectric field by subsequent growing EBL.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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Direct patterning of functional interfaces in oxide heterostructures

N. Banerjee, M. Huijben, G. Koster, and G. Rijnders

Appl. Phys. Lett. 100, 041601 (2012); http://dx.doi.org/10.1063/1.3679379 (3 pages) | Cited 5 times

Online Publication Date: 23 January 2012

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We report on the direct patterning of high-quality structures incorporating the LaAlO3-SrTiO3 interface by an epitaxial-liftoff technique avoiding any reactive ion beam etching. Detailed studies of temperature dependent magnetotransport properties were performed on the patterned heterostructures with variable thickness of the LaAlO3 layer and compared to their unstructured thin film analogues. The results demonstrate the conservation of the high-quality interface properties in the patterned structures enabling future studies of low-dimensional confinement on high mobility interface conductivity as well as interface magnetism.
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81.16.Rf Micro- and nanoscale pattern formation
68.35.Ct Interface structure and roughness
72.20.My Galvanomagnetic and other magnetotransport effects
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Characterization of thermal stresses in through-silicon vias for three-dimensional interconnects by bending beam technique

Suk-Kyu Ryu, Tengfei Jiang, Kuan H. Lu, Jay Im, Ho-Young Son, Kwang-Yoo Byun, Rui Huang, and Paul S. Ho

Appl. Phys. Lett. 100, 041901 (2012); http://dx.doi.org/10.1063/1.3678020 (4 pages) | Cited 4 times

Online Publication Date: 23 January 2012

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Through-silicon via is a critical element for three-dimensional (3D) integration of devices in multilevel stack structures. Thermally induced stresses in through-silicon vias (TSVs) have raised serious concerns over mechanical and electrical reliability in 3D technology. An experimental technique is presented to characterize thermal stresses in TSVs during thermal cycling based on curvature measurements of bending beam specimens. Focused ion beam and electron backscattering diffraction analyses reveal significant grain growth in copper vias, which is correlated with stress relaxation during the first cycle. Finite element analysis is performed to determine the stress distribution and the effect of localized plasticity and to account for TSV extrusion observed during annealing.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Electron trap liberation in MgF2 doped with Yb2+ using a two-color excitation experiment

P. S. Senanayake, J.-P. R. Wells, M. F. Reid, G. Berden, A. Meijerink, and R. J. Reeves

Appl. Phys. Lett. 100, 041902 (2012); http://dx.doi.org/10.1063/1.3678630 (3 pages)

Online Publication Date: 24 January 2012

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We utilize the optical transitions of Yb2+ excited by an ultraviolet optical parametric amplifier to probe electron trap liberation in MgF2 via the observation of a photoluminescence enhancement effect induced by a subsequent infrared pulse from a free-electron laser. The temperature dependence of the enhancement suggests that we liberate very shallow traps having a depth of approximately 17 cm−1. The observed “trap spectrum” is consistent with a simple model of a Coulomb trap.
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71.55.Ht Other nonmetals
78.55.Hx Other solid inorganic materials

Nanoscale diffraction imaging of the high-pressure transition in Fe1−xO

Yang Ding, Zhonghou Cai, Qingyang Hu, Hongwei Sheng, Jun Chang, Russell J. Hemley, and Wendy L. Mao

Appl. Phys. Lett. 100, 041903 (2012); http://dx.doi.org/10.1063/1.3679117 (4 pages)

Online Publication Date: 24 January 2012

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To further understand the long-debated origin of the high-pressure cubic-rhombohedral transition in FeO, we investigated the domain wall structure in Fe0.94O using high-pressure microdiffraction imaging techniques. The results reveal a non-reflection type domain wall structure forming due to the cubic-rhombohedral transition in Fe0.94O, which suggests the transformation could be associated with defects and is unlikely to be ferroelastic in nature.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
77.80.Dj Domain structure; hysteresis

The bound states of Fe impurity in wurtzite GaN

M. Zhang, T. F. Zhou, Y. M. Zhang, B. Li, S. N. Zheng, J. Huang, Y. P. Sun, G. Q. Ren, J. F. Wang, K. Xu, and H. Yang

Appl. Phys. Lett. 100, 041904 (2012); http://dx.doi.org/10.1063/1.3679133 (4 pages) | Cited 1 time

Online Publication Date: 24 January 2012

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A study on the bound states of Fe impurities in GaN by ultraviolet photoluminescence (PL) emissions is presented. Two elusive PL lines were observed at 3.463 eV (L1) and 3.447 eV (L2), respectively. The intensities of the two lines are proportional to the Fe concentration. The temperature dependence of L1 and L2 revealed acceptor-like and strong localized characteristic, respectively. Furthermore, Raman analysis indicated that L2 is correlated to an exciton bound to a nitride-vacancy (VN) related complex, i.e., [Fe2+-VN]. By co-doping with Si, the [Fe2+-VN]-related bound state will enable the spin-coupling between isolated iron ions.
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71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
61.72.jd Vacancies
61.72.sd Impurity concentration
61.66.Fn Inorganic compounds

Photoreflectance study of direct-gap interband transitions in Ge/SiGe multiple quantum wells with Ge-rich barriers

H. P. Hsu, P. H. Wu, Y. S. Huang, D. Chrastina, G. Isella, H. von Känel, and K. K. Tiong

Appl. Phys. Lett. 100, 041905 (2012); http://dx.doi.org/10.1063/1.3679608 (4 pages)

Online Publication Date: 26 January 2012

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Photoreflectance (PR) was used to study the direct-gap interband transitions in strain-compensated Ge/SiGe multiple quantum well (MQW) structures with Ge-rich SiGe barriers grown by low-energy plasma-enhanced chemical vapor deposition. The PR spectra revealed a wide range of possible optical transitions in the MQW structure. Detailed lineshape fits to the PR spectra and comparison to a theoretical calculation based on the envelope-function approximation with conduction band-offset and stain compensation factor as adjust parameters led to the identification of various interband transitions. The results demonstrated that PR is a powerful technique for nondestructive optical characterization of Ge/SiGe MQW structures.
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78.67.De Quantum wells
81.07.St Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.70.Fy Nondestructive testing: optical methods
78.66.Db Elemental semiconductors and insulators
78.66.Li Other semiconductors
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