Dynamic Tuning of Mean Carrier Momentum Relaxation Time in InGaAs InAlAs THz Photoconductive Switches

The carrier transport in InGaAs InAlAs multilayer heterostructures used for the implementation of terahertz (THz) photoconductive antennas is investigated under the injection of a continuous optical wave. By varying the amplitude level of the continuous optical wave in the transmitter or receiver antennas used in a conventional pulsed THz time-domain spectrometer, the amplitude of the detected photocurrent can be controlled without affecting its bandwidth. Unlike increasing the optical power of the pulsed signal, it is shown that raising the continuous optical power results in a reduction of the measured photocurrent. This lowering of the conductivity can be explained by changes in the instantaneous carrier momentum relaxation time in the material rather than variations of the free carrier density level. This behavior affects in systems showing optical continuous-wave components, as, for example, fiber-based THz time-domain spectrometers including optical amplifiers.