Electroacoustic conversion in modulation-doped SiGe/Si heterostructures

The temperature dependence of the efficiency of linear generation of acoustic waves by electric fields in modulation-doped Si1-xGex/Si heterostructures is investigated by the method of high-frequency hybrid acoustic spectroscopy at a frequency of similar to 225 MHz. It is shown that the conversion signal in the temperature region 4.2-150 K is due to the presence of space-charge regions in the structure and the Coulomb mechanism of excitation of longitudinal acoustic waves by an electric field normal to the surface of the planar structure. The influence of the Ge concentration x in coherently strained SiGe layers on the amplitude of the conversion signal is investigated. It is found that the effect is highly sensitive to variation of the index x in the interval 0.1 < x < 0.13. The influence of possible piezoactivity of the SiGe layers on the value of the conversion signal is discussed, as well as the influence on it of charges in deep traps near the Si/SiGe/Si interfaces.