Porosity dependence of the acoustic longitudinal velocity in heavily doped p ++ porous silicon layers

The longitudinal acoustic velocity for 1 GHz waves propagating along the 100 direction in p++ porous silicon layers has been measured using an acoustic wave transmission technique. The velocities obtained are significantly higher than those previously observed for p+ samples. The porosity dependence is measured to be VL = 8.43(l – P)0.58 km/s, where VL is longitudinal velocity and P is porosity. The low value of the exponent (0.58) is an indication of a relatively well-ordered pore structure. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)