Ultrafast acoustical gating of the photocurrent in a $p\text{−}i\text{−}n$ tunneling diode incorporating a quantum well

Ultrafast acoustic wave packets are used to control the photocurrent excited by a femtosecond optical pulse in a reverse biased ${\text{Al}}_x{\text{Ga}}_{1-x}\text{As}$ $p\text{−}i\text{−}n$ tunneling diode containing a GaAs quantum well in its intrinsic region. The change in photocurrent arises from the strain-induced shift of the quantum well excitonic resonance due to deformation potential electron-phonon coupling. This method of controlling electron transport on an ultrafast time scale could form the basis of a new class of terahertz electronic devices.

Figure 1

(Color online) (a) $I\text{−}V$ curves measured in the dark and under illumination for different wavelengths of CW optical excitation. The inset shows the optical and tunneling transitions in the QW in the applied electric field. (b) Bias dependence of the exciton resonance energy $E_0$ in the QW obtained from the position of peaks in the $I\text{−}V$ curves for various excitation wavelengths. The upper horizontal scale shows the electric field in the QW calculated from the experimental values of $E_0$.

Figure 2

(Color online) (a) The schematic diagram of ultrafast probing of the photocurrent changes in the $p\text{−}i\text{−}n$ structure, showing the bipolar strain pulses arriving at the QW due to the initial strain pulse and the pulse reflected from the top surface of the device. (b) The temporal traces (solid lines) of the relative photocurrent changes measured for two bias voltages $V$ and pump densities $W$. The dotted line shows the simulated temporal trace when the incident and reflected bipolar strain pulses pass through the QW.

Figure 3

(Color online) (a) The symbols show the dependencies of the amplitude $\Delta P$ of the ultrafast photocurrent changes on the reverse bias $V$ for two pump energy densities $W$. The dashed curve is the bias dependence of the photocurrent in the absence of the strain pulses. The inset shows the method of obtaining $\Delta P$ from the temporal signal $\Delta P\left(t\right)$. (b) The measured (symbols) for two strain pulse amplitudes ${\epsilon }_0$ and calculated (lines) dependences of the photocurrent sensitivity $\alpha$ to the strain. The solid and dashed lines correspond to the absorption spectra $A\left(\omega \right)$ shown in the inset by the solid and dashed lines respectively. The $\omega =0$ in the inset corresponds to the energy of the exciton resonance.