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Semiconductor Physics, Quantum Electronics & Optoelectronics. 2006. V. 9, N 3. P. 004-011.
Microacoustic evaluation of elastic parameters
of highly porous silicon layers
1Laboratoire des Semiconducteurs, Département de Physique, Faculté des Sciences,
Université Badji-Mokhtar, BP 12, Annaba, DZ-23000, Algeria
Abstract. Non-destructive scanning acoustic microscopy investigations of elastic
properties of porous silicon films, limited to low and medium porosities, are extended in
this work to higher porosities (80 %) corresponding to the appearance of room
temperature electroluminescence phenomena. Acoustic materials signatures were
measured at various operating frequencies, f, and film thickness, d. It was shown that as
these parameters increase the oscillatory V(z) behaviour disappears progressively to
become completely attenuated, for f = 565 MHz and d = 6 µm, due to wave absorption,
with αx = 0.2 µm−1
. Moreover, from high frequency microechography, it was possible to
determine longitudinal velocity, VL = 1680 m/s. To evaluate Young’s modulus, E, and
shear modulus, G, we used two different approaches to derive simple expressions for
these constants in terms of just VL. The validity of such expressions was successfully put
into evidence then applied to the highly porous silicon layers for which it was found that
E = 1.29 GPa and G = 0.63 GPa.
Keywords: porous Si, elastic constants, electroluminescence, acoustic microscopy,
surface acoustic wave.
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