Volume 91, Issue 23, 03 December 2007
- 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
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
quantum dot with an insulating gate" title="A few-electron vertical quantum dot with an insulating gate" />
Using an gate insulator by atomic layer deposition and air-bridge drain electrode, we fabricated a quantum dot with few electrons based on an resonant tunneling diode structure. Artificial atomic properties manifested themselves in magnetotransport, enabling the determination of effective electron factors. Results show that the insulating gate structure used here is effective for realizing quantum dots made of narrow-gap semiconductors for studying spin-related phenomena.
- LASERS, OPTICS, AND OPTOELECTRONICS
91(2007); http://dx.doi.org/10.1063/1.2816909View Description Hide Description
We demonstrate a compact, single-mode quantum cascade laser source continuously tunable between 8.7 and . The source consists of an array of single-mode distributed feedback quantum cascade lasers with closely spaced emission wavelengths fabricated monolithically on a single chip and driven by a microelectronic controller. Our source is suitable for a variety of chemical sensing applications. Here, we use it to perform absorption spectroscopy of fluids.
Large spectral tuning of liquid microdroplets standing on a superhydrophobic surface using optical scattering force91(2007); http://dx.doi.org/10.1063/1.2821145View Description Hide Description
We demonstrate large spectral tuning of glycerol/water microdroplets standing on a superhydrophobic surface using the optical scattering force exerted by a solid-state laser. Spectral tuning up to is presented in the whispering gallery modes as a result of the deformation of the microdroplets toward a truncated prolate spheroid geometry. Observed large spectral tuning is also reported to be highly reversible. This demonstration can inspire novel, largely tunable optical switches or filters based on liquid microdroplets kept in a sealed chamber.
91(2007); http://dx.doi.org/10.1063/1.2822889View Description Hide Description
We report on laser action of quantum well structures up to room temperature under optical pumping. Prerequisite is a novel annealing step increasing the radiative efficiency of the low-temperature grown structures by more than one order of magnitude. The carrier states involved are localized making the lasing properties temperature robust. The longest wavelength reached so far is .
Spatially resolved pump-probe second harmonic generation study of multilayer semiconductor heterostructures91(2007); http://dx.doi.org/10.1063/1.2821120View Description Hide Description
The transient electric-field-induced second harmonic generation change (TEFISHGC) signals from heterostructures measured in pump-probe configuration have been applied to monitor the interfacial electric fields arising from the charge separation of pump-induced carriers at the interfaces. The total intensity of the TEFISHGC signal is determined by the interference of contributions from both of the heterointerfaces. By changing the photon energy of the laser light over the GaAs absorption edge, the depth spatial resolution can be achieved allowing the ultrafast dynamics of interfacial electric field at each of the interfaces to be monitored separately.
91(2007); http://dx.doi.org/10.1063/1.2821833View Description Hide Description
We report a cheap and scalable bottom-up technique for fabricating wafer-scale, subwavelength-structured antireflection coatings on single-crystalline silicon substrates. Spin-coated monolayer colloidal crystals are utilized as shadow masks to generate metallic nanohole arrays. Inverted pyramid arrays in silicon can then be templated against nanoholes by anisotropic wet etching. The resulting subwavelength gratings greatly suppress specular reflection at normal incidence. The reflection spectra for flat silicon and the templated gratings at long wavelengths agree well with the simulated results using a rigorous coupled wave analysis model. These subwavelength gratings are of great technological importance in crystalline silicon solar cells.
91(2007); http://dx.doi.org/10.1063/1.2821834View Description Hide Description
A substrate removal technique using an InAsSb etch stop layer improves by a factor of 2 the quantum efficiency of back side illuminated type-II superlatticephotodetectors. After etching of the GaSb substrate with a based solution, the quantum efficiency of the diodes presents Fabry-Pérot oscillations averaging at 56%. Due to the confinement of the infrared light inside the devices, the quantum efficiency for certain devices reaches 75% at . The implementation of this new technique to a focal plane array resulted in a decrease of the integration time from .
91(2007); http://dx.doi.org/10.1063/1.2822395View Description Hide Description
Photoelectrochemical etching was used to measure the threading defect (TD) density in InGaNmultiple quantum welllight-emitting diodes(LEDs) fabricated from commercial quality epitaxial wafers. The TD density was measured in the LED active region and then correlated with the previously measured characteristics of these LEDs. It was found that the reverse leakage current increased exponentially with TD density. The temperature dependence of this dislocation-related leakage current was consistent with a hopping mechanism at low reverse-bias voltage and Poole-Frenkel emission at higher reverse-bias voltage. The peak intensity and spectral width of the LEDelectroluminescence were found to be only weakly dependent on TD density for the measured TD range of .
91(2007); http://dx.doi.org/10.1063/1.2822410View Description Hide Description
A high optical efficiency and wide-view transflective liquid crystal display based on fringe-field switching structure is proposed. The transmissive part has a homogenous liquid crystal(LC) alignment and is driven by a fringe electric field, which exhibits excellent electro-optic characteristics. The reflective part has a hybrid LC alignment with quarter-wave phase retardation and is also driven by a fringe electric field. Consequently, the transmissive and reflective parts have similar gamma curves.
91(2007); http://dx.doi.org/10.1063/1.2814062View Description Hide Description
The authors report on the fabrication of -based light emitting diodes(LEDs) on nanoscale silicon-on-insulator (SOI) substrates. The LED structures are grown on (111)-oriented thick SOI overlayer by metal organic chemical vapor deposition. Square-shaped mesa patterns are created by standard LED processing steps including multiple-mask photolithography, inductive coupled plasma etching, and contact metallization. Due to the high reflective beneath AlN buffer and high refractive contrasts at the interfaces, the authors observed multiple interference peaks from LEDs on SOI and such effect resulted in an increased integrated electroluminescence intensity when compared to LED structures fabricated on bulk Si(111).
Wavelength tuning the photonic band gap in chiral nematic liquid crystals using electrically commanded surfaces91(2007); http://dx.doi.org/10.1063/1.2820681View Description Hide Description
In this letter, the authors demonstrate photonic band gap(PBG) tuning in chiralnematic liquid crystals using electrically commanded surfaces consisting of a ferroelectric liquid crystal. The electrically commanded surfaces generate a contraction of the pitch of the chiral nematic which is manifested as a blueshift of the PBG. Results are presented which demonstrate that tuning can be achieved by either varying the frequency or the amplitude of the electric field. The maximum shift observed for the long-wavelength band edge was for an electric field strength of and a frequency of .
91(2007); http://dx.doi.org/10.1063/1.2817755View Description Hide Description
We report the efficient generation of femtosecond pulses from a diode-pumped solid-state laser that has been passively mode locked using a quantum-dot-based saturable absorber. Average output powers up to and transform-limited pulses as short as were obtained around with a pulse repetition frequency of from a diode-pumped laser. The InGaAs quantum-dot saturable absorber was characterized to have a saturation fluence of and nonsaturable losses of less than 0.2% with an initial low-signal absorption of 2.5% at .
91(2007); http://dx.doi.org/10.1063/1.2820384View Description Hide Description
In this letter, we report the fabrication of deep -cut periodically poled lithium niobate (PPLN) crystal. The technique relies on ridges performed by wet etching to improve poling field penetration into the substrate and, hence, to provide more depth to inverted domains. Based on this approach, domain inversions as deep as were achieved. As an application, reverse proton exchanged waveguides were fabricated on top of the PPLN to demonstrate efficient second harmonic generation in the near infrared. A conversion efficiency as high as was measured near .
91(2007); http://dx.doi.org/10.1063/1.2822817View Description Hide Description
The growth of ZnO-on-GaN heterostructures was implemented using the vapor cooling condensation system. The technique thus developed was employed to fabricate both the and heterojunctionlight-emitting diodes(LEDs). A rectifying diodelike behavior was clearly observed from both the and heterojunctionLEDs, with the forward turn-on voltage of and the reverse breakdown voltage of determined for the heterojunctionLEDs, compared to 7 and , respectively, for the heterojunctionLEDs. Based on the results of photoluminescence and electroluminescence studies conducted on these LED structures, the ZnO layer responsible for the peak emission wavelength of were also verified experimentally.
91(2007); http://dx.doi.org/10.1063/1.2822442View Description Hide Description
Measurements of light-output power versus current are performed for light-emitting diodesgrown on GaN-on-sapphire templates with different threading dislocation densities. Low-defect-density devices exhibit a pronounced efficiency peak followed by droop as current increases, whereas high-defect-density devices show low peak efficiencies and little droop. The experimental data are analyzed with a rate equation model to explain this effect. Analysis reveals that dislocations do not strongly impact high-current performance; instead they contribute to increased nonradiative recombination at lower currents and a suppression of peak efficiency. The characteristics of the dominant recombination mechanism at high currents are consistent with processes involving carrier leakage.
91(2007); http://dx.doi.org/10.1063/1.2822808View Description Hide Description
We report on experimental and theoretical studies of the stability regime of passive mode-locked quantum dot lasers, which is decisively larger than in quantum well lasers. A small range of -switched instability is observed at low gain currents. Transition to switching is inhibited due to fast damping of the relaxation oscillations. A double pulse mode-locking regime appears for longer cavities, and exhibits bistability and coupling to the fundamental mode-locking operation.
Hydrothermal method grown large-sized zinc oxide single crystal as fast scintillator for future extreme ultraviolet lithography91(2007); http://dx.doi.org/10.1063/1.2815920View Description Hide Description
The scintillation properties of a hydrothermal method grown zinc oxide (ZnO) crystal are evaluated for extreme ultraviolet(EUV) laser excitation at wavelength. The exciton emission lifetime at around is determined to be , almost identical to ultraviolet laser excitation cases. This fast response time is sufficiently short for characterizing EUVlithography light sources having a few nanoseconds duration. The availability of large size ZnO crystal up to is quite attractive for future lithography and imaging applications.
91(2007); http://dx.doi.org/10.1063/1.2823584View Description Hide Description
We report on the coupling of optical transitions between excited conduction subbands in heterostructures with the resonant photonic mode of a semiconductor microcavity. The coupling is found to increase with temperature, owing to the thermal excitation of carriers from the ground subband and, thanks to the large dipole-matrix element of the excited-state transition, a record splitting of is shown in the room-temperature reflectance. The importance of translating the angle-dependent spectra into energy-wavevector dispersion when the coupling is so large is highlighted, and a theoretical fitting procedure is used to extract the value of the vacuum-field Rabi energy.
- PLASMAS AND ELECTRICAL DISCHARGES
91(2007); http://dx.doi.org/10.1063/1.2820451View Description Hide Description
We demonstrated enhancement of in-band conversion efficiency (CE) at of the extreme ultraviolet(EUV) emission from a tin (Sn) cavity target irradiated by a laser pulse. Whereas a planar Sn target produced an in-band CE of around 2%, the use of cavity targets significantly enhanced the EUV emission energy and the EUV CE. An EUV CE of 4% was observed for a Sn cavity target with a depth of which is one of the highest values ever reported.
91(2007); http://dx.doi.org/10.1063/1.2820444View Description Hide Description
We have developed a low-energy Ar fast atom source consisting of a surface waveplasma (SWP) source and two carbonelectrodes with a diameter of . Ions were extracted from the SWP using two carbonelectrodes, accelerated and injected to the process chamber and then neutralized by charge exchangereaction without energy loss. Characteristics of the Ar ions and Ar fast atoms were investigated using quadrupole mass spectroscopy with an energy analyzer. Energies of Ar fast atoms were successfully controlled from by varying the acceleration voltage applied at the carbonelectrode.