Volume 98, Issue 12, 21 March 2011
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- 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:
Heterogeneous integration of dissimilar single crystals is of intense research interests. Lattice mismatch has been the most challenging bottleneck which limits the growth of sufficient active volume for functional devices. Here, we report self-assembled, catalyst-free, single crystalline GaAs nanoneedles grown on sapphire substrates with 46% lattice mismatch. The GaAs nanoneedles have a 2–3 nm tip, single wurtzite phase, excellent optical quality, and dimensions scalable with growth time. The needles have the same sharp, hexagonal pyramid shape from (1.5 min growth) to length (3 h growth).
- LASERS, OPTICS, AND OPTOELECTRONICS
98(2011); http://dx.doi.org/10.1063/1.3570634View Description Hide Description
An enhanced stimulated emission was observed in optically pumped GaNnanopillars. The nanopillars were fabricated from an epitaxial wafer by patterned pillar etching followed by crystalline regrowth. Under optical excitation, a strong redshiftedstimulated emission peak emerged from a broad spontaneous emission background. The emission is attributed to the electron-hole plasma gain at high carrier density. The emission slope efficiency was greatly enhanced by 20 times compared with a GaN substrate under the same pumping condition. The enhancement is attributed to the better photon and gain interaction from the multiple scattering of photons among nanopillars.
98(2011); http://dx.doi.org/10.1063/1.3569819View Description Hide Description
We report on high performance InAs/InP quantum dot tunable external cavity lasers (ECLs) operating in continuous-wave mode at room temperature. A tuning range of 70 nm has been achieved, covering the wavelengths from 1563 to 1633 nm. The threshold current densities are lower than in the tuning range. More than 23 mW output power was obtained at lasing wavelength of 1594 nm with an external differential quantum efficiency of 10.3%. An even wider tuning range of 98 nm has been obtained from the ECL based on the QD laser lasing in a longer wavelength.
Deterministic integrated tuning of multicavity resonances and phase for slow-light in coupled photonic crystal cavities98(2011); http://dx.doi.org/10.1063/1.3571283View Description Hide Description
We present the integrated chip-scale tuning of multiple photonic crystalcavities. The optimized implementation allows effective and precise tuning of multiple cavity resonances (up to ) and intercavity phase by direct local temperature tuning on suspended silicon nanomembranes. Through designing the serpentine metal electrodes and careful electron-beam alignment to avoid cavity mode overlap, the coupled photonic crystalcavities preserve their high quality factors. The deterministic resonance and phase control enables switching between the all-optical analog of electromagnetically-induced-transparency to flat-top filter lineshapes, with future applications of trapping photons and optoelectronic modulators.
98(2011); http://dx.doi.org/10.1063/1.3568892View Description Hide Description
We develop a technique based on a micromachined photoconductive probe-tip to characterize a terahertz (THz) porous fiber. Losses less than are measured in the frequency range from 0.2 to 0.35 THz, with the minimum of at 0.24 THz. Normalized group velocity greater than 0.8, which corresponds to dispersion values in between −1.3 and for are obtained. Moreover, we directly measure the evanescent electric field as a function of frequency. Good agreement between the measured curves and expected theoretical values indicates the low invasiveness of the applied probe-tip.
98(2011); http://dx.doi.org/10.1063/1.3560466View Description Hide Description
Single-shot nanometer-scale imaging techniques have become important because of their potential application in observing the structural dynamics of nanomaterials. We report here the image reconstruction results obtained using single-shot Fourier transform x-rayholography with an x-ray laser driven by a table top laser system. A minimum resolution of 87 nm was obtained from the reconstructed image. We could also discriminate the aggregates of carbon nanotubes, which shows the feasibility of single-exposure nanoimaging for real specimens using a laser-driven x-ray laser.
98(2011); http://dx.doi.org/10.1063/1.3570687View Description Hide Description
We report on a three color heterojunctionband gap engineered type-II InAs/GaSb strained-layer superlattice photodiode for short-wave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR) detection. The reported structure is a three contact device with nBn architecture for SWIR and MWIR and heterojunction PIbN architecture for LWIR detection. At 77 K, the cutoff wavelength for SWIR, MWIR, and LWIR regions are , , and , respectively. The reported architecture can be used for simultaneous detection in the LWIR/MWIR and LWIR/SWIR bands as well as sequential detection in the MWIR/SWIR bands by switching the polarity of the applied bias.
Terahertz-frequency photoconductive detectors fabricated from metal-organic chemical vapor deposition-grown Fe-doped InGaAs98(2011); http://dx.doi.org/10.1063/1.3571289View Description Hide Description
We report the detection of terahertz frequency radiation using photoconductive antennas fabricated from Fe-doped InGaAs,grown by metal-organic chemical vapor deposition. Coherent photoconductive detection is demonstrated using femtosecond laser pulses centered at either an 800 or a 1550 nm wavelength. The InGaAsresistivity and the sensitivity of photoconductive detection are both found to depend on the Fe-doping level. We investigate a wide range of probe laser powers, finding a peak in detected signal for probe power, followed by a reduction at larger powers, attributed to screening of the detected THz field by photo-generated carriers in the material. The measured signal from Fe:InGaAs photoconductive detectors excited at 800 nm is four times greater than that from a low-temperature-grown GaAs photodetector with identical antenna design, despite the use of a ten times smaller probe power.
Surface segregation effects of erbium in GaAs growth and their implications for optical devices containing ErAs nanostructures98(2011); http://dx.doi.org/10.1063/1.3565168View Description Hide Description
We report on the integration of semimetallic ErAs nanoparticles with high optical quality GaAs-based semiconductors,grown by molecular beam epitaxy. Secondary ion mass spectrometry and photoluminescence measurements provide evidence of surface segregation and incorporation of erbium into layers grown with the erbium cell hot, despite the closed erbium source shutter. We establish the existence of a critical areal density of the surfaceerbium layer, below which the formation of ErAs precipitates is suppressed. Based upon these findings, we demonstrate a method for overgrowing ErAs nanoparticles with III-V layers of high optical quality, using subsurface ErAs nanoparticles as a sink to deplete the surfaceerbium concentration. This approach provides a path toward realizing optical devices based on plasmonic effects in an epitaxially-compatible semimetal/semiconductor system.
98(2011); http://dx.doi.org/10.1063/1.3571446View Description Hide Description
We demonstrate large cavity-enhanced optical Stark shifts for a single quantum dot(QD) coupled to a photonic crystalcavity. A maximum Stark shift of 20 GHz is observed for a QD detuned by 104 GHz from the cavity mode. These Stark shifts are attained with extremely low cavity field energies of only ten photons. The changes in the QD emission wavelength are monitored via nonresonant transfer between the QD and cavity mode. Experimental results are compared to theoretical predictions based on the solution to the full master equation and found to be in excellent agreement.
98(2011); http://dx.doi.org/10.1063/1.3568888View Description Hide Description
The spatial motion and effective duration of a traveling plasma grating formed by two interfering femtosecond laser filaments in gases is characterized by its Doppler effect imparted on a probe pulse. The shift velocity determined experimentally agrees with the theoretical calculations.
98(2011); http://dx.doi.org/10.1063/1.3569587View Description Hide Description
We demonstrate a technique for achieving spectral resonance between a polarization-degenerate micropillar cavity mode and an embedded quantum dot transition. Our approach is based on a combination of isotropic and anisotropic tensile strain effected by laser-induced surface defects, thereby providing permanent tuning. Such a technique is a prerequisite for the implementation of scalable quantum information schemes based on solid-state cavity quantum electrodynamics.
98(2011); http://dx.doi.org/10.1063/1.3570630View Description Hide Description
In the framework of effective mass Hamiltonian of semiconductorquantum wellstructures and band anticrossing model, we investigated the band structures of fully strained quantum wells. The could be widely modified to be direct-band gap or indirect-band gap by changing the mole fraction of As and N in the well layer. We found that an increase in the N mole fraction in the well layer increases the TE mode optical gain very slightly.
98(2011); http://dx.doi.org/10.1063/1.3570642View Description Hide Description
Electroluminescence(EL) from a laterally suspended nano ZnO dot (LSNZD) integrated between two microfabricated atomically sharp probe-tips is presented. When driven by of bias current, the LSNZD emitted light, which was easily observed by the naked eye at room temperature. The minimum number of photons emitted per a second from the LSNZD was at 100 nA of current, when driven by 12.5 V. The light emission mechanism and electrical characteristics of the LSNZD are explained with a metal-semiconductor-metal model. An optical wavelength spectrum of the emitted light shows major bands of emitted photons between 580 and 750 nm, which indicates the electron transitions from defects in the ZnO band gap. The device fabrication is compatible with typical integrated circuit processes and is suitable for chip- scale optoelectronics.
Modulating the fundamental inductive-capacitive resonance in asymmetric double-split ring terahertz metamaterials98(2011); http://dx.doi.org/10.1063/1.3571288View Description Hide Description
We investigate resonant transmission of planar asymmetric metamaterials made from double split-ring resonators. As the symmetry of the unit cell resonator is broken by displacing the two gaps away from the center in opposite directions, a giant amplitude modulation is observed at the fundamental inductive-capacitive resonance due to strong polarization conversion. The modulation is nearly absent when the gaps are moved together in the same direction. This effect persists in metamaterials with different structural designs. These asymmetric metamaterials may open up new avenues toward the control of terahertz waves and the development of modulator and polarizer based terahertz devices.
The effect of trimethylgallium flows in the AlInGaN barrier on optoelectronic characteristics of near ultraviolet light-emitting diodes grown by atmospheric pressure metalorganic vapor phase epitaxy98(2011); http://dx.doi.org/10.1063/1.3571440View Description Hide Description
The letter reports a theoretical and experimental study on the device performance of near ultraviolet light-emitting diodes(LEDs) with quaternary AlInGaN quantum barrier (QB). The indium mole fraction of AlInGaN QB could be enhanced as we increased the trimethylgallium flow rate. It was found the AlInGaN/InGaN LEDs can reduce forward voltage and improve light output power, compared with conventional GaN QB. By using advanced device simulation, it should be attributed to a reduction in lattice mismatch induced polarization mismatch in the active layer, which results in the suppression of electron overflow.
98(2011); http://dx.doi.org/10.1063/1.3571442View Description Hide Description
It is shown that the metallic disk structure can be used as an efficient narrow-band thermal emitter in the IR region. The absorption spectra of such structure are investigated both theoretically and experimentally. Calculations of thermal radiation properties of the metallic disk show that the metallic disk is a perfect emitter at a specific wavelength, which can be tuned by varying the diameter of the disk. The metallic disk exhibits only one significant localized surface plasmonpolariton (LSPP) mode for both TM and TE polarizations simultaneously. The LSPP mode can be tuned by either varying the disk diameter or the spacer (made of ).
Improved performance of GaN metal-semiconductor-metal ultraviolet detectors by depositing nanoparticles on a GaN surface98(2011); http://dx.doi.org/10.1063/1.3567943View Description Hide Description
GaNmetal-semiconductor-metal (MSM) ultraviolet detectors were investigated by depositing different density of nanoparticles (SNPs) on the GaN. It was shown that the dark current of the detectors with SNPs was more than one order of magnitude lower than that without SNPs and the peak responsivity was enhanced after deposition of the SNPs. Atomic force microscopy observations indicated that the SNPs usually formed at the termination of screw and mixed dislocations, and further current-voltage measurements showed that the leakage of the Schottky contact for the GaN MSM detector decreased with deposited the SNPs. Moreover, the leakage obeyed the Frenkel–Poole emission model, which meant that the mechanism for improving the performance is the SNPs passivation of the dislocations followed by the reduction in the dark current.
98(2011); http://dx.doi.org/10.1063/1.3571285View Description Hide Description
The authors report on a theoretical investigation of guided polariton states arising from the strong coupling between quantum-well excitons and a Bloch surface wave confined at the interface between a uniform dielectric medium and a Bragg mirror. It is shown that the exciton–photon coupling is almost doubled as compared to a similar structure made in a conventional planar microcavity. It is also shown that, by simple engineering of the sample surface with silicon oxide deposition, one can efficiently produce one-dimensional polaritons propagating within the structure with extremely low losses. The latter result evidences the usefulness of Bloch surface waves as a key component for the realization of “polaritonic integrated circuits.”
Efficient parametric terahertz generation in quasi-phase-matched GaP through cavity enhanced difference-frequency generation98(2011); http://dx.doi.org/10.1063/1.3571550View Description Hide Description
We report an efficient parametric terahertz (THz) source by using bonded quasi-phase-matched (QPM) GaP crystals pumped by the C-band pulsed fiber lasers in a master oscillator power amplifier configuration, based on difference frequency generation (DFG). We observed that the QPM-GaP crystals can effectively increase the THz generation power and efficiency by increasing the number of periods. Moreover, we observed external cavity enhanced THz DFG by placing the QPM-GaP crystal in an external ring cavity. The THz cavity enhancement factor of approximately 250 has been achieved in comparison with a single-pass THz DFG. The maximum THz average power can reach , corresponding to a power conversion efficiency of and a quantum efficiency of 3.16%.
- PLASMAS AND ELECTRICAL DISCHARGES
98(2011); http://dx.doi.org/10.1063/1.3571292View Description Hide Description
By introducing some ideas of magnetohydrodynamics(MHD) and kinetic theories, some useful solutions for electron-density distribution in the radial direction in multicusp ion source are obtained. Therefore, some conclusions are made in this perspective: 1, the electron-density distributions in a specific region in the sheath are the same with or without magnetic field; 2, the influence of magnetic field on the electron density obeys exponential law, which should take into account the collision term as well if the magnetic field is strong; 3, the result derived from the Boltzmann equation is qualitatively consistent with some given experimental results.