Oa. Mironov et al., OBSERVATION OF PIEZOELECTRIC-LIKE BEHAVIOR IN COHERENTLY STRAINED B-DOPED(100)SIGE SI HETEROSTRUCTURES/, Journal of crystal growth, 157(1-4), 1995, pp. 382-385
In the present work tile hybrid acoustic spectroscopy technique has be
en used to demonstrate the conversion of a high frequency (HF) electri
c field into acoustic waves and to provide the first direct observatio
n of the piezoelectric effect in the SiGe/Si strained layer system. Th
e sample was a p-type modulation doped Si0.88Ge0.12/Si heterostructure
containing a two-dimensional hole gas with carrier sheet density 2 x
10(11) cm(-2) and a 4.2 K mobility of 10 500 cm(2) V-1 s(-1). It was e
xcited with a 225.7 MHz high frequency pulse of 1 mu s duration and 0.
5 W peak power. The amplitude of the output acoustic signal was about
110 dB below the electromagnetic input signal at 77 K. We believe that
the observed electric field-acoustic conversion is associated with th
e non-centrosymmetric structure of the ordered unit cell of the strain
ed SiGe alloy. Additionally we report on phonon Raman scattering at T
= 300 K and hot hole Shubnikov-de Haas and zero magnetic field resisti
vity behaviour in the same heterostructures in the temperature range o
f 0.35 to 1.4 K. A broad band near 255 cm(-1) and a peak near 435 cm(-
1) have been attributed to a particular Si-Ge ordering within the allo
y layer. The energy relaxation of the carriers has been measured and i
s found to be dominated by a weakly screened piezoelectric coupled aco
ustic-phonon mechanism, thereby providing further evidence of ordering
in the SiGe alloy.