S. Winnerl

Broadband semiconductor superlattice detector for THz radiation

We report on a broadband GaAs/AlAs superlattice detector for THz radiation; a THz field reduces the current through a superlattice, which is carried by miniband electrons, due to modulation of the Bloch oscillations of the miniband electrons. We studied the detector response, by use of a free electron laser, in a large frequency range (5–12 THz). The responsivity showed strong minima at frequencies of infrared active phonons of the superlattice. A theoretical analysis of the detector delivers an understanding of the role of phonons and gives a characterization of the responsivity.

Frequency doubling and tripling of terahertz radiation in a GaAs/AlAs superlattice due to frequency modulation of Bloch oscillations

We report on frequency doubling and tripling of THz radiation in a voltage-biased GaAs/AlAs superlattice. By use of a corner cube antenna system, radiation from the Santa Barbara free-electron laser (frequency 0.7 THz) was guided into a superlattice mesa element and the second and third harmonic were coupled out of the mesa. Without bias only radiation of the third harmonic was generated, while the biased superlattice emitted radiation of both the second and third harmonic. We attribute the harmonic generation to frequency modulation of damped Bloch oscillations of the miniband electrons in the superlattice.

Ultrafast detection and autocorrelation of picosecond THz radiation pulses with a GaAs/AlAs superlattice

We used a wide miniband GaAs/AlAs superlattice (at room temperature) for detection and autocorrelation of picosecond THz radiation pulses (frequency 4.3 THz) from a free-electron laser. The detection was based on a THz-field induced change in conductivity of the superlattice, and the correlation on the nonlinearity of the conductivity change at strong THz-pulse-power. The nonlinear conductivity change was due to two effects, which we attribute to dynamical localization of miniband electrons and to ionization of deep impurity centers.

Millimeter wave generation with a quasi planar superlattice electronic device

Abstract We report on millimeter wave generation with a superlattice electronic device (SLED) operated at room temperature. The SLED, containing a wide-miniband GaAs/AlAs superlattice, had a quasi planar structure with two terminals lying in one plane. The device showed a negative differential conductance, due to Bloch oscillations of the miniband electrons. The SLED, mounted into a waveguide, delivered radiation in the 50 to 60xa0GHz range, with a maximum power (400xa0μW) corresponding to an efficiency of 1%. Additionally, harmonic radiation up to frequencies above 200xa0GHz was observed. We associate the generation of radiation with current oscillation caused by traveling dipole domains. We also present an analysis, taking elastic and inelastic scattering into account, of the miniband electrons, indicating that our SLED should, in principle, be suitable for generation of radiation up to 1xa0THz.

Superlattice frequency multiplier for generation of submillimeter waves

We observed frequency multiplication of 65-GHz radiation up to the fifth harmonic (325 GHz; wavelength 0.9 mm) in a superlattice with negative differential conductance at room temperature. The efficiency of multiplication depended strongly on both the strength of a static field and the strength of the 65-GHz field. An analysis of the results shows that the nonlinear current, responsible for the frequency multiplication, was governed by the Esaki-Tsu current-voltage characteristic that describes the transport of carriers in large-miniband superlattices.

Differential electronic gating: A method to measure the shape of short THz pulses with a poorly defined trigger signal

A simple experimental method has been developed to determine the shape of repetitive picosecond THz pulses in the presence of a large jitter in the trigger signal. This method, a modification of the recently reported differential optical gating method, is based on the femtosecond electronic gating of a high-frequency sequential oscilloscope. As a test, the shape of THz pulses from the free-electron laser has been measured.

Superlattice detector as a fast direct detector and autocorrelator for terahertz radiation

We report on a GaAs/AlAs superlattice detector as a novel direct detector and autocorrelator for THz radiation. It is based on a doped wide-miniband GaAs/AlAs superlattice, with submonolayer AlAs barrier layers; the superlattice is operated at room temperature. THz radiation, generated by a free-electron laser and a mode locked p-Ge laser, was coupled into the superlattice via a corner cube antenna system. THz-irradiation of the biased superlattice resulted in a current reduction, which was monitored. The direct detector showed a fast response (20 ps, limited by the electronic circuit) and was robust against intense radiation pulses (peak power 10 kW). The responsivity was 100 times higher than the responsivity of detectors of comparable risetime and comparable robustness. Intense THz radiation caused a complete suppression of the current through the superlattice. This is the basis of the superlattice autocorrelator. The superlattice autocorrelator could resolve picosecond radiation pulses.