Sub-picosecond acoustic pulses at buried GaP/Si interfaces

We report on the optical generation and detection of ultrashort acoustic pulses that propagate in three-dimensional semiconductor crystals. Photoexcitation of lattice-matched GaP layers grown on Si(001) gives rise to a sharp spike in transient reflectivity due to the acoustic pulse generated at the GaP/Si interface and detected at the GaP surface and vice versa. The extremely short width of the reflectivity spike, 0.5 ps, would translate to a spatial extent of 3 nm or 10 atomic bilayers, which is comparable with the width of the intermixing layer at the GaP/Si interface. The reflectivity signals are also modified by quasi-periodic Brillouin oscillations arising from the propagation of the acoustic pulses in the GaP and Si crystals. The present results demonstrate the potential applications of the simple optical pump-probe scheme in the nondestructive evaluation of the buried semiconductor interface quality. Published by AIP Publishing.