We present a terahertz (THz) photoconductive emitter structure, which employs a n-doped layer underneath a low-temperature-grown GaAs region to enable the THz transient to couple vertically through a defined mesa. A nonlinear bias dependence is observed, yielding an order in magnitude improvement in power for a mesa device with a 100 μm2 area over a conventional planar control reference device at 32 V and 5 mW illumination power. We relate the bias dependence of the THz signal to the breakdown voltage observed in the current-voltage characteristic. Reducing the antenna gap size through reducing the thickness of the low temperature-GaAs region below 1 μm shows a large improvement in the bandwidth of the device, with an enhancement of the normalized intensity between 0.2 to 2 THz for a bow-tie antenna geometry.

We report the use of a multilayered structure comprising of alternating layers of low temperature grown GaAs and high temperature grown AlAs, as a terahertz (THz) photoconductive antenna emitter and receiver. Devices based on 10×10 μm2 mesa defined photoconductive gaps were fabricated on the multilayered structure, and a comparison made to conventional planar devices. The mesa defined photoconductive antennas allowed successive contact through the multilayered structure, which resulted in an increase in THz emission power and detection responsivity with increasing number of layers in contact with the antenna electrodes. A comparison with a conventional single layered device, processed in an identical mesa geometry, confirmed that the enhancement in THz emission is solely due to the multilayered nature of the device, whereas the improved receiver performance can be partially attributed to the mesa geometry.

We present a study into the properties of terahertz (THz) emission and detection using low temperature grown GaAs photoconductive switches over a range of ex situ anneal temperatures. Our analysis focuses on the effect of defect saturation, which has been confirmed in many experiments. However its effect on the THz emission and detection has so far not been fully investigated. In this letter, we examine the dependence of the radiated THz pulse width (full width at half maximum) upon optical power, and show that the differences in the characteristics with annealing can be theoretically accounted for when defect saturation is taken into account. Defect saturation was found to substantially increase the trapping time of photoexcited electrons, which in turn can cause THz pulse broadening at high optical powers. This effect was found to increase with anneal temperature due to the decrease in defect density. The radiated peak THz amplitude from emitters increases monotonically with increasing optical power across the range of anneal temperatures investigated. In the detector configuration, however, the detected peak THz amplitude reaches a maximum before starting to decrease with increasing optical power. The latter trend was observed for devices annealed at temperatures higher than 300 °C and is attributed to the onset of defect saturation.