Volume 98, Issue 23, 06 June 2011
- 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:
Subwavelength electroluminescent sources with spatial, spectral, and polarization controlling capabilities are critical elements for optical imaging and lithography beyond the diffraction limit. Here, we show that the electroluminescence from single, strain-free InGaN nanodisks embedded in self-assembled GaNnanorods can span the entire visible spectrum with a large linear polarization ratio . Furthermore, this unique nanodisk-in-nanorod geometry enables the realization of the ultrasmall footprint light-emitting diodes(LEDs) to be used as subwavelength light sources. Using these nano-LEDs, we are able to demonstrate near-field, subwavelength photolithography by controlling the exposure time and light intensity from single InGaN nanodisks at chosen wavelengths.
- LASERS, OPTICS, AND OPTOELECTRONICS
98(2011); http://dx.doi.org/10.1063/1.3596704View Description Hide Description
We have studied the possibility to utilize semiconductor quantum dots(QDs) as an optical phase shifter within a vertical geometry for ultrafast information processing. From theoretical analyses, an optical phase nonlinearity in QD structures has been predicted which can be enhanced through the use of an vertical optical cavity. Asymmetric cavity structures with 16/30 periods of GaAs/AlGaAs layers for the front/back mirrors have been fabricated to demonstrate a practical device with significant nonlinear characteristics for optical switching. A phase shift of 18° has been initially observed with a tilted pump scheme. This observation paves the way toward a Mach–Zehnder optical switch using QDs inside a vertical cavity.
High-performance quantum cascade lasers with wide electroluminescence , operating in continuous-wave above98(2011); http://dx.doi.org/10.1063/1.3596706View Description Hide Description
The authors report high temperature continuous-wave (cw) operations of broad-gain quantum cascade lasers based on the anticrossed dual-upper-state to multiple-lower-state design. The devices exhibit extremely wide electroluminescence () and subthreshold amplified spontaneous emissionspectra at room temperature. Despite showing such broad electroluminescencespectra, the high-reflection coated, buried heterostructure lasers operating at demonstrate a low threshold current density of and a high power of with a high slope efficiency of in cw mode at 300 K. The maximum cw operating temperature of above is achieved.
98(2011); http://dx.doi.org/10.1063/1.3597793View Description Hide Description
We present a random number generation scheme that uses broadband measurements of the vacuum field contained in the radio-frequency sidebands of a single-mode laser. Even though the measurements may contain technical noise, we show that suitable algorithms can transform the digitized photocurrents into a string of random numbers that can be made arbitrarily correlated with a subset of the quantum fluctuations (high quantum correlation regime) or arbitrarily immune to environmental fluctuations (high environmental immunity). We demonstrate up to 2 Gbps of real time random number generation that were verified using standard randomness tests.
Resilience of gated avalanche photodiodes against bright illumination attacks in quantum cryptography98(2011); http://dx.doi.org/10.1063/1.3597221View Description Hide Description
Semiconductor avalanche photodiodes(APDs) are commonly used for single photon detection in quantum key distribution. Recently, many attacks using bright illumination have been proposed to manipulate gated InGaAsAPDs. In order to devise effective countermeasures, careful analysis of these attacks must be carried out to distinguish between incorrect operation and genuine loopholes. Here, we show that correctly operated, gated APDs are immune to continuous-wave illumination attacks, while monitoring the photocurrent for anomalously high values is a straightforward countermeasure against attacks using temporally tailored light.
Tuneable polaritonics at room temperature with strongly coupled Tamm plasmon polaritons in metal/air-gap microcavities98(2011); http://dx.doi.org/10.1063/1.3597304View Description Hide Description
We report strong coupling between Tamm plasmons and excitons in III–V quantum wells at room temperature in ultracompact sample designs. A high refractive index contrast air-gap mirror together with optical Tamm states at a metal/semiconductor interface tightly confines the intracavity field leading to substantial local field enhancements. Angular-resolved reflectivityspectra give clear evidence for anticrossing in the dispersion relation. Room temperature Rabi splittings of 10 meV are found in excellent agreement with simulations. Electrical control of the polariton modes is realized without need for doped mirror layers. Such air-gap microcavities open innovative possibilites for electrically tunable microcavities and polaritonic microelectromechanics.
81 fJ/bit energy-to-data ratio of 850 nm vertical-cavity surface-emitting lasers for optical interconnects98(2011); http://dx.doi.org/10.1063/1.3597799View Description Hide Description
Extremely energy-efficient oxide-confined high-speed 850 nm vertical-cavity surface-emitting lasers for optical interconnects are presented. Error-free performance at 17 and 25 Gb/s via a 100 m multimode fiber link is demonstrated at record high dissipation-power-efficiencies of up to 69 fJ/bit and 99 fJ/bit, respectively. These are the most power efficient high-speed directly modulated light sources reported to date. The total energy-to-data ratio is 83 fJ/bit at and reduces to 81 fJ/bit at . These results were obtained without adjustment of driving conditions. A high -factor of and a -factor of 0.41 ns are measured.
98(2011); http://dx.doi.org/10.1063/1.3596437View Description Hide Description
We demonstrate engineering the photocharge generation efficiency of nanoparticles on the nanometer scale by using a type-II band-gap structure. Compared to bare CdSe cores, the dispersion of type-II core/shell nanoparticles in photorefractive polymer led to an average 100% increase in photocurrents. An improvement to the refractive-index construction time, and a near 100% enhancement to the two beam coupling net-gain coefficients and four-wave mixing internal diffraction efficiencies have been achieved at moderate biases.
98(2011); http://dx.doi.org/10.1063/1.3598961View Description Hide Description
We report continuous wave lasing operation at of subwavelength-metallic-cavities with semiconductor core encapsulated in silver under electric injection. The physical cavity volumes of the two lasers presented are and , respectively. Longitudinal modes observed in one of lasers correspond to the Fabry–Perot cavity in the length direction. Such record high temperature operation of a subwavelength laser is of great importance for the development of small light sources in future integrated photonic circuits and other on-chip applications.
98(2011); http://dx.doi.org/10.1063/1.3599518View Description Hide Description
A frequency tunable terahertz heterodynespectrometer, based on a third-order distributed feedback quantum cascade laser as a local oscillator, has been demonstrated by measuring molecular spectral lines of methanol gas at 3.5 THz. By varying the bias voltage of the laser, we achieved a tuning range of of the lasing frequency, within which the molecular spectral lines were recorded. The measured spectra show excellent agreement with modeled ones. By fitting we derived the lasing frequency for each bias voltage accurately. The ultimate performance of the receiver including the resolution of noise temperature and frequency is also addressed.
98(2011); http://dx.doi.org/10.1063/1.3597627View Description Hide Description
We predict highly efficient third harmonic generation through simultaneous phase-matching of second-harmonic generation and sum-frequency generation in lithium niobate nanowaveguides, enabled due to strong modal dispersion. We demonstrate that the waveguide size which corresponds to phase-matching is also optimal for highest mode confinement and therefore for strongly enhanced conversion efficiency.
To realize the optimal probe pulse length for detection of pulsed terahertz signal with spectral-encoding technique98(2011); http://dx.doi.org/10.1063/1.3598405View Description Hide Description
The approach to realize the optimal chirped probe pulse length for an arbitrary pulsed terahertz (THz) signal measured with the spectral-encoding technique was investigated by simulation. It was found that either the maximum positive peak or the absolute value of the strongest negative peak of the normalized difference between the probe spectrum modulated by THz signal and the background probe spectrum tended to be maximized when the probe pulse duration approached to the optimal value. The probe pulse length can be adjusted continuously with a pair of triangular dispersive prisms. THz signals from high-voltage biased air plasmas induced by femtosecond laser pulse were measured with minimum distortion using our simple method.
Low temperature near-field scanning optical microscopy on infrared and terahertz photonic-crystal quantum cascade lasers98(2011); http://dx.doi.org/10.1063/1.3597411View Description Hide Description
We report the development of a scattering-type near-field scanning optical microscope (sNSOM) which operates at temperatures down to 100 K with a scanning range of up to . We have used this sNSOM to map the electromagnetic near-field on mid-IR and terahertz (THz) surface emitting quantum cascade lasers with photonic-crystal resonators. Mid-IR devices operate at (40 THz) while THz devices operate at (2.7 THz). The near-field images—in agreement with numerical calculations—demonstrate an instrument resolution of 100's nm.
98(2011); http://dx.doi.org/10.1063/1.3598404View Description Hide Description
We describe subwavelength-resolved measurements of the broadband terahertz field propagating inside a finite-width parallel-plate waveguide. We observe a transition in the spatial mode of the waveguide, in which the energy distribution shifts from the waveguide center to the edges with increasing frequency. This transition is surprisingly abrupt, and depends sensitively on the gap between the waveguide plates. These results may have important implications for a variety of terahertz experiments as well as in the design of optical systems and components in the visible and near-infrared regimes, which rely on plasmonicwave guiding.
Transition from strong to ultrastrong coupling regime in mid-infrared metal-dielectric-metal cavities98(2011); http://dx.doi.org/10.1063/1.3598432View Description Hide Description
We have investigated the transition from strong to ultrastrong coupling regime between a mid-infrared intersubband excitation and the fundamental mode of a metal-dielectric-metal microcavity. The ultrastrong coupling regime is demonstrated up to room temperature for a wavelength of by using 260 nm thick cavities, which impose an extreme subwavelength confinement. By varying the doping of our structures we show that the experimental signature of the transition to the ultrastrong coupling regime is the opening of a photonic gap in the polaritondispersion. The width of this gap depends quadratically on the ratio between the Rabi and intersubband transition energies.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
98(2011); http://dx.doi.org/10.1063/1.3592822View Description Hide Description
We measure the thermal boundary conductance across Al/Si and interfaces that are subjected to varying doses of protonion implantation with time domain thermoreflectance. The protonirradiation creates a major reduction in the thermal boundary conductance that is much greater than the corresponding decrease in the thermal conductivities of both the Si and substrates into which the ions were implanted. Specifically, the thermal boundary conductances decrease by over an order of magnitude, indicating that protonirradiation presents a unique method to systematically decrease the thermal boundary conductance at solid interfaces.
98(2011); http://dx.doi.org/10.1063/1.3592801View Description Hide Description
The distribution of electric field in GaN(cap)/AlGaN/GaN(buffer) transistor heterostructures with various AlGaN layer thicknesses (10, 20, and 30 nm) has been studied by contactless electroreflectance and compared with theoretical calculations performed for various positions of the Fermi-level on GaNsurface. For the three samples the best agreement between experimental data and theoretical calculations has been found at the same position of the Fermi-level on GaNsurface (i.e., below the conduction band). It means that the Fermi-level is pinned on GaNsurface and this pinning can be treated as the boundary condition for the distribution of polarization-related fields in this heterostructure.
98(2011); http://dx.doi.org/10.1063/1.3597301View Description Hide Description
We demonstrate the ability to release the growth-induced strain in (Ga,Mn)As layers and (In,Ga)As/(Ga,Mn)As bilayers by lifting them from the GaAs substrate. The lifted (bi)layers are then deposited back onto various substrates. The change in strain before and after processing has been studied by means of x-ray diffraction. Magnetic characterization demonstrates the efficiency of our lift-off process to reorient the magnetization to the direction normal to the layer plane.
98(2011); http://dx.doi.org/10.1063/1.3597223View Description Hide Description
Thin membranes with excellent optical properties are essential elements in diamond based photonic systems. Due to the chemical inertness of diamond, ion beam processing must be employed to carve photonic structures. One method to realize such membranes is ion-implantation graphitization followed by chemical removal of the sacrificial graphite. The interface revealed when the sacrificial layer is removed has interesting properties. To investigate this interface, we employed the surface sensitive technique of grazing angle channeled Rutherford backscattering spectroscopy. Even after high temperature annealing and chemical etching a thin layer of damaged diamond remains, however, it is removed by hydrogen plasma exposure.
In situ synchrotron based x-ray fluorescence and scattering measurements during atomic layer deposition: Initial growth of on Si and Ge substrates98(2011); http://dx.doi.org/10.1063/1.3598433View Description Hide Description
The initial growth of was studied by means of synchrotron based in situx-ray fluorescence(XRF) and grazing incidence small angle x-ray scattering (GISAXS). was deposited by atomic layer deposition(ALD) using tetrakis(ethylmethylamino)hafnium and on both oxidized and H-terminated Si and Gesurfaces.XRF quantifies the amount of deposited material during each ALD cycle and shows an inhibition period on H-terminated substrates. No inhibition period is observed on oxidized substrates. The evolution of filmroughness was monitored using GISAXS. A correlation is found between the inhibition period and the onset of surface roughness.
98(2011); http://dx.doi.org/10.1063/1.3597302View Description Hide Description
Medium-range order in metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during crystallization process of metallic glass.