PIEZOELECTRIC EFFECT IN COHERENTLY STRAINED B-DOPED (001)SIGE SI HETEROSTRUCTURES/

We report on two methods which illustrate piezoelectric effects in the strained Si (100)Si-1-x/Ge-x system. The non-contact sound excitation technique has been used to reveal the conversion of a high-frequency electric field E into acoustic waves at 77 K which can also be modulat ed by a de applied bias voltage (+/-30 V). The sample was an MBE grown modulation doped Si0.88Ge0.12/(001)Si structure with a carrier sheet density 2.0 x 10(11) cm(-2) and a 4.2 K mobility 10500 cm(2)V(-1)s(-1) . We deduce that the observed high-frequency electric field acoustic w ave conversion is associated with a piezoelectric-like effect possibly due to ordering in the strained SiGe alloy or symmetry breaking effec t near Si/SiGe interface. Further evidence is provided by the existenc e of a piezoelectric phonon interaction in the hot hole energy relaxat ion mechanism determined from high electric field Shubnikov de Haas He -3 low temperature measurements.