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 modulated by a dc applied bias voltage (±30 V). The sample was an MBE grown modulation doped Si_{0.88}Ge_{0.12}/(001)Si structure with a carrier sheet density 2.0 × 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 wave conversion is associated with a piezoelectric-like effect possibly due to ordering in the strained SiGe alloy or symmetry breaking effect near Si/SiGe interface. Further evidence is provided by the existence of a piezoelectric phonon interaction in the hot hole energy relaxation mechanism determined from high electric field Shubnikov de Haas He^{3} low temperature measurements.
An anomaly of the in-plane conductivity is observed in the superlattices PbTe/SnTe on (001)KCl in the temperature region of 60-130 K. The anomaly is caused by a structural phase transition in SnTe layer and as a result, the transition induced formation of defects. These defects are additional scattering centres which decrease the superlattice conductivity.
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