Ultrafast carrier diffusion in gallium arsenide probed with picosecond acoustic pulses - art. no. 081202

We describe an experimental investigation of the generation and detection o f picosecond acoustic-phonon pulses in a thin slab of GaAs using ultrashort optical pulses. Comparison of the optical phase variation with a simple th eory for ambipolar diffusion indicates that carrier diffusion has a signifi cant effect on the shape of the phonon pulses generated. The phonon pulse d uration is measured to be similar to 25 ps, four times longer than that exp ected from optical-absorption considerations alone, indicating that hot car riers penetrate more than 100 nm into the sample during the phonon pulse ge neration process.