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Compact and tunable semiconductor terahertz sources providing direct electrical control, efficient operation at room temperatures and device integration opportunities are of great interest at the present time. One of the most well-established techniques for terahertz generation utilises photoconductive antennas driven by ultrafast pulsed or dual-wavelength continuous wave laser systems, though some limitations, such as confined optical wavelength pumping range and thermal breakdown, still exist. The use of quantum dot-based semiconductor materials, having unique carrier dynamics and material properties, can help to overcome limitations and enable efficient optical-to-terahertz signal conversion at room temperatures. Here we discuss the construction of novel and versatile terahertz transceiver systems based on quantum dot semiconductor devices. Configurable, energy-dependent optical and electronic characteristics of quantum-dot-based semiconductors are described, and the resonant response to optical pump wavelength is revealed. Terahertz signal generation and detection at energies that resonantly excite only the implanted quantum dots opens the potential for using compact quantum dot-based semiconductor lasers as pump sources. Proof-of-concept experiments are demonstrated here that show quantum dot-based samples to have higher optical pump damage thresholds and reduced carrier lifetime with increasing pump power. [ABSTRACT FROM AUTHOR]

We report on the performance of photoconductive terahertz detectors made from low temperature grown GaAs (LTG GaAs) and Ga0.7In0.3As (LTG GaInAs) in the wavelength range from 620 to 1550 nm. These THz detectors exhibited a significant sub-bandgap photoconductivity due to the electron transitions from the defect band. A simple model evaluating picosecond photoconductivity was proposed to explain the experimental data. By comparing the modeling results with the experimental data, the defect band position was found to be at 0.77 and at 0.4 eV below the conduction band minimum for LTG GaAs and LTG GaInAs, respectively. [ABSTRACT FROM AUTHOR]

Terahertz time-domain spectroscopy (TDS) system based on femtosecond Yb:KGW laser, photoconductive emitters and detectors made using low-temperature-grown (LTG) GaAs layers annealed at moderate temperatures (∼400 °C) was demonstrated. Measured photoexcited charge carriers concentration of these layers increased lineary with an optical power, showing that the transitions from defect band to conduction band are dominant. The largest amplitude THz pulse was emitted by the device made from the LTG-GaAs layer annealed at 420 °C temperature with useful signal bandwidth reaching 3 THz. On the other hand, detectors made from this material were more than an order of magnitude less sensitive than conventional GaBiAs detectors (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The influence of thermal annealing on optical properties and carrier lifetime of dilute GaBixAs1-x layers was investigated. Thick (0.5-1.5 μm) relaxed and thin (30-100 nm) strained bismide layers were grown onto semi-insulating (100)-oriented GaAs substrates by molecular beam epitaxy (MBE) using As4 and As2, respectively. The post-growth annealing was carried out in the rapid thermal annealing (RTA) oven at the temperatures ranging from 550 °C to 750 °C under nitrogen atmosphere. The high resolution X-ray diffraction (HRXRD), photoluminescence (PL) and optical pump-THz probe measurements revealed two different GaBixAs1-x anneal mechanisms. The annealing at temperatures higher than 600 °C caused a significant reduction of carrier lifetime of relaxed bismide layers with x > 0.05. Meanwhile, thick layers with a smaller content of Bi (x < 0.05) and thin strained layers annealed up to 600 °C still exhibited long carrier lifetimes. On the other hand, the significant photoluminescence signal increase at room and liquid nitrogen temperatures was observed for the GaBiAs layers grown using As2 (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]