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Carrier transport features in single-wall carbon nanotube (SWCNT) films under strong electric fields (up to 105 V/cm) are presented. Application of electrical pulses of nanosecond duration allowed to minimize Joule heating and resolve intrinsic nonlinearities with the electric field. Investigations within a wide range of temperatures-4.2-300 K-indicated that carrier localization as well as tunneling through the insulating barriers between conducting regions takes place in SWCNT films. Crossover from semiconducting behavior to metallic behavior in strong electric field is described using the fluctuation induced tunneling model and assuming that the conducting regions demonstrate characteristic metallic conductivity. [ABSTRACT FROM AUTHOR]

Noise properties of beryllium delta-doped GaAs/AlAs multiple quantum wells, doped both above and below the Mott transition, are studied within the frequency range of 10 Hz-20 kHz and at temperature from 77 K to 350 K. It is shown that the generation-recombination noise in structures close to the Mott transition exhibits two peaks-a frequency and temperature-dependent peak between 120 and 180 K and a broadband, frequency- and temperature- nearly independent peak around 270 K. Activation energies are estimated; origin of the broadband maximum is attributed to holes tunnelling into defect trap states located in the AlAs barrier/GaAs quantum well interface. [ABSTRACT FROM AUTHOR]

Suitability of InGaAs-based bow-tie diodes for a spectroscopic terahertz imaging is demonstrated by inspecting explosive simulators packed in a thick plastic container. The transmission images were obtained within the frequency range of 0.58-2.52 THz at room temperature using optimized bow-tie diode connection scheme. Content of sucrose and tartaric acid in the test samples was discriminated. Measured absorbance was found to be in a good correlation with Fourier spectroscopy data. Performance of room temperature THz imaging using the bow-tie diode was compared versus a commercial pyro-electric sensor. [ABSTRACT FROM AUTHOR]

Electrically tunable metamaterial modulation based on double split-ring resonators fabricated on GaAs substrate is studied experimentally and numerically. Monochromatic terahertz radiation is effectively modulated in transmission and reflection modes; experiments are complemented by measurements employing time-domain terahertz spectroscopy. Upper modulation frequency was found at 10 kHz. [ABSTRACT FROM AUTHOR]

The pulsed optoelectronic terahertz emitter based on a δ-doped p-i-n-i GaAs/AlxGa1-xAs heterostructure, which was suggested by Reklaitis [Phys. Rev. B 77, 153309 (2008)], is investigated experimentally. It is shown that the heterostructure can serve as efficient antenna- and bias-free surface emitter. Its power exceeds the emission from InGaAs and InAs surfaces for optical excitation fluences below 0.7 μJ/cm2 at 82 MHz pulse repetition rate, respectively, 7 μJ/cm2 at 1 kHz, with potential for further improvement by carrier recombination management. [ABSTRACT FROM AUTHOR]

A silicon-lens coupled bow-tie InGaAs-based diode with broken symmetry is demonstrated for terahertz imaging applications below 1 THz at room temperature. Transient features and the dynamic range of the bow-tie InGaAs-based sensor are explored experimentally, proving the possibility to use the device in real-time imaging systems. Response time is found to be less than 7 ns, responsivity of 0.1 mA/W, and noise equivalent power of 5.8 nW/√Hz. [ABSTRACT FROM AUTHOR]

The authors present an experimental study of the time resolved photocurrent and its Fourier spectrum in dc-biased semi-insulating GaAs under multiple high-field domains photoexcitation. It is observed that nanosecond duration light interference pattern induces subnanosecond instabilities on the falling slope of the photocurrent pulse only when the external dc field reaches a threshold field value, i.e., when a transient multi-domain structure drifting through the spatially modulated semiconductor is generated. The signal spectrum in the gigahertz range is broad but, if system parameters are set properly, the spectrum becomes stable and concentrated at a single frequency proportional to the spatial period of the light interference pattern and the drift velocity of the domains. [ABSTRACT FROM AUTHOR]

We have studied the phase locking and spectral linewidth of an ∼2.7 THz quantum cascade laser by mixing its two lateral lasing modes. The beat signal at about 8 GHz is compared with a microwave reference by applying conventional phase lock loop circuitry with feedback to the laser bias current. Phase locking has been demonstrated, resulting in a narrow beat linewidth of less than 10 Hz. Under frequency stabilization we find that the terahertz line profile is essentially Lorentzian with a minimum linewidth of ∼6.3 kHz. Power dependent measurements suggest that this linewidth does not approach the Schawlow-Townes limit. [ABSTRACT FROM AUTHOR]

A passive detection scheme for broadband, 10 GHz–2.52 THz, sensing at room temperature is demonstrated using a hemispherical silicon lens-coupled diode of an asymmetrically-shaped bow-tie geometrical form. The device is fabricated from an MBE-grown In0.54Ga0.46As wafer as mesas of 3 µm depth produced by wet etching. The detector exhibits voltage sensitivity about 5 V/W below 1 THz. [ABSTRACT FROM AUTHOR]

The need to reach single-mode lasing and minimize at the same time the electrical dissipation of cryogenically operated terahertz quantum cascade lasers may result in small and subwavelength cavity dimensions. To assess the influence of such dimensions on the shape of the laser emission, we have measured the beam pattern of two metal-metal cavity quantum cascade lasers. The patterns show regular angular intensity variations which depend on the length of the laser cavity. The physical origin of these features is discussed in terms of interference of the coherent radiation emitted by end and side facets of the laser bar. [ABSTRACT FROM AUTHOR]

An approach to probe magnetic component of microwave radiation via sub-harmonic mixing in high-Tc superconductor Bi2Sr2CaCu2O8 layer is suggested. The recording principle is illustrated showing the relation between the amplitude of the mixing signal and the microwave magnetic field component in a standing-wave experiment at 9.1 GHz frequency performed close to the transition temperature Tc. [ABSTRACT FROM AUTHOR]