Observation of strain in pseudomorphic Si1−xGex by tracking phonon participation in Si∕SiGe resonant interband tunnel diodes via electron tunneling spectroscopy

Abstract

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 4nm of intrinsic Si0.60Ge0.40 and n nm of intrinsic Si (n=4,6,8,10) all grown on Si substrates, the transverse acoustic (TA) phonon of Si0.60Ge0.40 was identified and the energy was measured to be 16±1meV. This is higher than the ∼14meV energy of the TA phonon in Si0.60Ge0.40 reported from measurements of Esaki tunnel diodes fabricated from bulk single crystals. The increase is attributed to the compressive strain in the Si0.60Ge0.40 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.