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 $\text{}_{1-x}$/Ge$\text{}_{x}$ 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 $\text{}_{0.88}$Ge$\text{}_{0.12}$/(001)Si structure with a carrier sheet density 2.0 × 10 $\text{}^{11}$ cm$\text{}^{-2}$ and a 4.2 K mobility 10500 cm$\text{}^{2}$ V$\text{}^{-1}$ s$\text{}^{-1}$. 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$\text{}^{3}$ low temperature measurements.