Carriers dynamics measurements in ultrafast photoconductive switches for THz applications

We present experimental characterization and numerical simulation of metal-semiconductor-metal type ultrafast photoswitches made from low temperature grown GaAs doped with beryllium (LT-GaAs:Be). Generation and detection of electrical pulses are performed using a femtosecond laser source and a photoconductive sampling set up that involves nonlinear effect in the structure. Following the expected picosecond electrical response a longer relaxation tail is clearly detected. Our model shows that this long term effect is due to a contribution of free holes, which lifetime can reach hundredth of picoseconds.