Nonequilibrium phonons in SiGe quantum-well nanostructures upon excitation by picosecond laser pulses

The phonon pulses initiated by photoexcitation of structures containing Si0.8Ge0.2 double quantum wells under picosecond radiation of a MIRA 900P titanium-sapphire laser (λ = 760 nm) are studied. The propagation of nonequilibrium acoustic phonons is detected with a superconducting bolometer. The recorded bolometer response is found to differ substantially from that observed in photoexcitation of the same structure by nanosecond pulses of a nitrogen laser (λ = 337 nm). The generation of coherent acoustic phonons is suggested as an explanation.