Picosecond strain pulses probed by the photocurrent in semiconductor devices with quantum wells

Ultrafast acoustic wave packets are detected by probing the photocurrent in semiconductor devices containing quantum wells. The strain pulses were generated by thermalization of a femtosecond laser pulse in a thin metal film deposited on the surface of the GaAs substrate opposite to the semiconductor device. The probing was realized by measuring the photocurrent excited by a femtosecond optical pulse with photon energy close to the excitonic resonance of the quantum well. Two types of devices are used: a reverse biased (AlGa)As p-i-n tunneling diode containing a GaAs quantum well in its intrinsic region and a planar device containing an (InGa)As quantum well. The change in photocurrent arises from the strain-induced shift of the quantum well excitonic resonance due to deformation potential electron-phonon coupling. The method has a picosecond temporal resolution, shows a high sensitivity to subterahertz acoustic wave packets and has potential for ultrafast control of electrical conductance in semiconductor devices.