Observation of strain in pseudomorphic Si_1-xGe_x by tracking phonon participation in Si/SiGe resonant interband tunnel diodes via electron tunneling spectroscopy

High-sensitivity and low-noise electron tunneling spectroscopy was used to measure the phonon spectra via band-to-band tunneling in Si/SiGe resonant interband tunneling diodes (RITD), tracking the effects of the weighted average Ge percentage in the central tunneling spacer. With a composite RITD tunneling barrier consisting of 4 nm of intrinsic Si_0.60Ge_0.40 and n nm of intrinsic Si (n=4,6,8,10) all grown on Si substrates, the transverse acoustic (TA) phonon of Si_0.60Ge_0.40 was identified and the energy was measured to be 16±1 meV. This is higher than the ∼14 meV energy of the TA phonon in Si_0.60Ge_0.40 reported from measurements of Esaki tunnel diodes fabricated from bulk single crystals. The increase is attributed to the compressive strain in the Si_0.60Ge_0.40 layer grown on Si substrates. The observation of the upshift of phonon energy with strain by electron tunneling spectroscopy demonstrates the capability of electron tunneling spectroscopy to characterize residual strain.