Strong picosecond ultrasonic responses of semiconductors probed close to interband transitions

We present experimental and numerical results of picosecond ultrasonic experiments performed in different semiconductors at different laser wavelengths. We first come back on the strong oscillations which appear in the reflectivity curves of silicon as the probe pulse is tuned in the blue range. We show that they come from an effect of the electronic transitions on the piezo-optic couplings. We then present similar results obtained in germanium which displays three interband transitions which fall in our laser source tuning range: 3.11, 2.11 and 0.8 eV (399, 587 and 1540 nm). Here again we have noticed strong responses in the reflectivity curves. We then make a comparison between silicon and germanium in respect with the laser wavelength effects. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)