Volume 96, Issue 20, 17 May 2010
- lasers, optics, and optoelectronics
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- organic electronics and photonics
- device physics
- biophysics and bio-inspired systems
- interdisciplinary and general physics
Index of content:
A deterministic design of an ultrahigh -factor, wavelength-scale photonic crystal nanobeam cavity is proposed and experimentally demonstrated. Using this approach, cavities with and on-resonance transmission are designed. The devices, fabricated in silicon and capped with a low refractive indexpolymer, have experimental and . This is, to the best of our knowledge, the highest transmission measured in deterministically designed, wavelength-scale high-cavities.
- LASERS, OPTICS, AND OPTOELECTRONICS
Optical transmission of periodic annular apertures in metal film on high-refractive index substrate: The role of the nanopillar shape96(2010); http://dx.doi.org/10.1063/1.3427390View Description Hide Description
The influence of annular aperture parameters on the optical transmission through arrays of coaxial apertures in a metal film on high refractive index substrates has been investigated experimentally and numerically. It is shown that the transmission resonances are related to plasmonic crystal effects rather than frequency cutoff behavior associated with annular apertures. The role of deviations from ideal aperture shape occurring during the fabrication process has also been studied. Annular aperture arrays are often considered in many applications for achieving high optical transmission through metal films and understanding of nanofabrication tolerances are important.
96(2010); http://dx.doi.org/10.1063/1.3430039View Description Hide Description
n-ZnO/p-GaN heterojunctionlight-emitting diodes with and without a sandwiched AlN layer were fabricated. The electroluminescence(EL)spectrum acquired from the n-ZnO/p-GaN displays broad emission at 650 nm originating from ZnO and weak emission at 440 nm from GaN, whereas the n-ZnO/AlN/p-GaN exhibits strong violet emission at 405 nm from ZnO without GaN emission. The EL intensity is greatly enhanced by inserting a thin AlN intermediate layer and it can be attributed to the suppressed formation of the interfacial layer and confinement effect rendered by the AlN potential barrier layer.
96(2010); http://dx.doi.org/10.1063/1.3427485View Description Hide Description
The polarizationentanglementphoton pairs generated from the biexciton cascade decay in a single semiconductorquantum dot is distorted due to the fine structure splitting. We show that, frequency of light can be shifted when it passes through an electro-optic modulator under voltage ramping. Based on this, we can realize polarization-dependent frequency shift and the hidden entanglement due to fine structure splitting can be revealed.
96(2010); http://dx.doi.org/10.1063/1.3432071View Description Hide Description
We describe the fabrication and measurement of a terahertz surface plasmonwaveguide in which the optical mode is localized within a nanoporoussilicon slab. We compare the propagation characteristics among waveguides with different porous layer thickness, and present an analytical model that accurately describes the dispersion and loss in the waveguides.
96(2010); http://dx.doi.org/10.1063/1.3429681View Description Hide Description
A multilayer quantum dot sample has been excited with a strong terahertz (THz) electric field and probed with a near-infrared(NIR) laser. First- and second-order THz optical sidebands are generated on the NIR probe beam by driving quantum dot intersublevel resonances with the THz fields. A conversion efficiency of was obtained for the conversion of NIR power into sideband emission at 4 K, decreasing by a factor of 20 up to room temperature. The sideband emission wavelength can be tuned over by selection of appropriate NIR and THz frequencies, due to the inhomogeneous broadening of the dot ensemble.
96(2010); http://dx.doi.org/10.1063/1.3427438View Description Hide Description
InGaN-based light-emitting diodes(LEDs) were grown and fabricated on nanoscale patterned Si (111) substrates (NPSi). Using anodized aluminum oxide as the etch mask, the NPSi was prepared with an average nanopore diameter of 150 nm and interpore distance of 120 nm. LEDsgrown on NPSi exhibit relaxed tensile stress relative to the ones grown on microscale patterned Si (111) substrates (MPSi). Nanoheteroepitaxial lateral overgrowth was significantly promoted on NPSi, which led to extensive dislocation bending and annihilation. The devices made on NPSi exhibit lower leakage current and higher light output power as compared with those on MPSi.
96(2010); http://dx.doi.org/10.1063/1.3430510View Description Hide Description
In this letter, we propose a high speed and ultralow driving voltage traveling wave electro-optic (EO) modulator based on a dual horizontal slot waveguide. The proposed design harnesses the unique properties of ferroelectric materials such as and exotic, organic EO polymers to tightly confine both the optical and rf modes in a nanoscale slot maximizing the nonlinear interaction with the electric field. Larger electrode separation allows for significant reduction in rf propagation loss. Simulations of the half-wavelength voltage-length product and electro-optic response of the proposed device reveal ultrabroadband operation, up to 250 GHz, and subvolt driving voltage for a 1 cm long modulator.
96(2010); http://dx.doi.org/10.1063/1.3432072View Description Hide Description
The operation of an all-optical magnetic switching based on the paramagnetic crystals is carried out by the time-resolved magneto-opticalFaraday effect. Our results demonstrate that the switching time can be as fast as at room temperature. The switching amplitude shows a linear dependence on the excitation intensity, which is proportional to the magnetization induced by the circularly polarized light. Based on the inverse Faraday effect in magneto-optical crystal, the switching mechanisms arising from circular dichroism and birefringence are discussed. By tailoring the magneto-opticalproperties of crystal, the switching magnitude can be modulated.
Conduction and transmission analysis in gold nanolayers embedded in zinc oxide for flexible electronics96(2010); http://dx.doi.org/10.1063/1.3435467View Description Hide Description
Gold-embedded zinc oxide structures are obtained in which the conduction mechanism changes from conduction through the oxide and activated tunneling between discontinuous metal islands to metallic conduction through a near-continuous layer, with increase in gold thickness. These structures can show resistivity as low as . Optical transmission is elucidated in terms of gold’s absorption due to interband electronic transitions, and free carrier absorption losses combined with limitation of the mean free path in discontinuous nanoparticles. The structures show transmittance, photopic averaged transmittance, and Haacke figure of merit values of 93%, 84%, and , respectively.
Temperature performance analysis of terahertz quantum cascade lasers: Vertical versus diagonal designs96(2010); http://dx.doi.org/10.1063/1.3430741View Description Hide Description
Resonant phonon depopulation terahertz quantum cascade lasers based on vertical and diagonal lasing transitions are systematically compared using a well established ensemble Monte Carlo approach. The analysis shows that for operating temperatures below 200 K, diagonal designs may offer superior temperature performance at lasing frequencies of about 3.5 THz and above; however, vertical structures are more advantageous for good temperature performance at lower frequencies.
Enhancement of ultraviolet electroluminescence based on isotype heterojunction with low threshold voltage96(2010); http://dx.doi.org/10.1063/1.3431287View Description Hide Description
Ultraviolet light-emitting diodes based on simple isotype heterojunction have been fabricated using a radio frequency magnetron sputtering system. Ultraviolet emission peaking around with a full-width at half maximum of was observed at room temperature when the devices were under sufficient forward bias. With the presence of an layer inserted between the ZnO and GaN layers, the ultraviolet emission intensity and output power have been much enhanced, while the threshold voltage drops down to 2.5 V. The electroluminescence mechanisms in these devices were discussed in terms of the band diagrams of the heterojunctions.
96(2010); http://dx.doi.org/10.1063/1.3431665View Description Hide Description
We present a metal/semiconductor beam steering device for use in the mid-infrared wavelength range. We demonstrate how changing the frequency of the incident light results in a smoothly varying shift in the angular distribution of the transmitted beam, and we present an analysis of the beam profile for a number of different wavelengths. Finally we verify that a similar steering effect is achieved with fixed frequency incident light and a modification of the permittivity of the semiconductor substrate, ultimately resulting in a 3° shift in the transmitted beam angle for minimal shifts in the semiconductorpermittivity.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
Mechanisms controlling the phase and dislocation density in epitaxial silicon films grown from silane below96(2010); http://dx.doi.org/10.1063/1.3422474View Description Hide Description
We construct a phase diagram for silicon layer growth on (001) Si by hot-wire chemical vapor deposition (HWCVD), for rates from 10 to 150 nm/min and for substrate temperatures from 500 to . Our results show that a mixed mono and dihydride surface termination during growth causes polycrystallinegrowth; some H-free sites are needed for epitaxy. For epitaxialfilms, the dislocation density decreases with increasing growth temperature because of reduced O contamination of the surface. The best HWCVD epitaxial layers have dislocation densities of .
The electronic consequences of multivalent elements in inorganic solar absorbers: Multivalency of Sn in96(2010); http://dx.doi.org/10.1063/1.3427433View Description Hide Description
Multivalent transition metal impurities in semiconductors are known to create deep levels inside the band gap that are associated with changes in the oxidation state. Some emerging functional semiconductor materials now contain multivalent elements not just as impurities, but as part of their structural skeleton (“multivalent semiconductors”). This raises the possibility that the performance of such materials may be affected by those skeleton elements transitioning from one oxidation state to another, in response to charge-altering perturbations such as illumination or doping. Here we address the correlation between multivalency and the electronic properties of these new semiconductor materials.
Electronic structure of wurtzite and rocksalt InN investigated by optical absorption under hydrostatic pressure96(2010); http://dx.doi.org/10.1063/1.3431291View Description Hide Description
The pressure dependence of the optical absorption edge of InN is investigated. Owing to the strong nonparabolicity of the energy bands, wurtzite InN exhibits enhanced optical absorption well above the absorption edge. The direct band gap of wurtzite InN increases linearly with pressure at . The wurtzite-to-rocsksalt phase transition is observed at as a clear change in the absorption edge. We find that rocksalt InN is an indirect semiconductor with a band gapenergy of around 1.0 eV. A higher energy direct transition is found at . These results are discussed in terms of theoretical band-structure calculations.
96(2010); http://dx.doi.org/10.1063/1.3430509View Description Hide Description
The mechanism for thermally stable indium-containing silver [Ag(In)] Ohmic contact on -type GaN has been investigated. The specific contact resistivity as low as and a high reflectance of 88.4% at a 460 nm wavelength were obtained by annealing Ag(0.5 wt % In) alloy contact at in air ambient. The In atoms in Ag matrix made In–O chemical bonds, producing a tensile stress in the film. This compensated thermal compressive stress built in the Ag film. As a result, In atoms in Ag film play a role in preventing Ag contact from agglomeration, leading to high reflectance and good thermal stability.
96(2010); http://dx.doi.org/10.1063/1.3430524View Description Hide Description
We study the leakage dynamics of charge stored in an ensemble of CdTe quantum dots embedded in a field-effect structure. Optically excited electrons are stored and read out by a proper time sequence of bias pulses. We monitor the dynamics of electron loss and find that the rate of the leakage is strongly dependent on time, which we attribute to an optically generated electric field related to the stored charge. A rate equation model quantitatively reproduces the results.
96(2010); http://dx.doi.org/10.1063/1.3429084View Description Hide Description
The dissolution of interstitial-type end-of-range (EOR) damage in preamorphized Ge is shown to induce a transient enhanced diffusion of an epitaxially grown boron delta at temperatures above that saturates above . The B diffusion events are quantitatively correlated with the measured positive strain associated with the EOR damage as a function of the annealing temperature with an energy barrier for the EOR damage dissolution of . These results unambiguously demonstrate that B diffuses in Ge through a mechanism assisted by self-interstitials, and impose considering the interstitial implantation damage for the modeling of impurity diffusion in Ge.
96(2010); http://dx.doi.org/10.1063/1.3432398View Description Hide Description
We investigated the influence of oxygen deficiency on the Fermi level of ZnO thin film prepared by pulsed laser deposition (PLD). For this purpose, we adopted in situ x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The oxygen deficiency was effectively controlled by varying the oxygen partial pressure during the PLD. The shifted by as the decreased from 10 to 3.3 Pa. This shift indicates a significant change in the energy balance in the oxygen-deficient ZnO films. This fact suggests that the very large change in the resistivity of ZnO thin films resulting from the oxygen deficiency could be attributed to the shift rather than grain boundary formation in the ZnO film.
96(2010); http://dx.doi.org/10.1063/1.3432408View Description Hide Description
M-plane GaNavalanche photodiodes on low dislocation density freestanding m-plane GaN substrates were realized using metal-organic chemical vapor deposition. High quality homoepitaxial m-plane GaN layers were developed; the root-mean-square surface roughness was less than 1 Å and the full-width-at-half-maximum value of the x-ray rocking curve for diffraction of m-plane GaN epilayer was 32 arcsec. High quality material led to a low reverse-bias dark current of 8.11 pA for mesa photodetectors prior to avalanche breakdown, with the maximum multiplication gain reaching about 8000.