Phonon-assisted tunneling in silicon/silicon-germanium resonant interband tunnel diodes
Abstract (Summary)Electron tunneling spectroscopy was applied toward Si/SiGe resonant interband tunnel diodes (RITDs) to ascertain the phonon spectra of the composite tunneling barrier which consists of Si1-xGex and Si layering. Two issues were identified: the error in the second-order derivative which would reduce the measurement sensitivity, and the contact resistance which would aect phonon energy measurement. A harmonic detection system was used to measure the rst-order derivative with an accuracy of 10^-4, followed by first-order numerical differentiation to obtain high quality second-order derivative. Contacts to silicon using nickel silicide (NiSi) and delta doping technique were studied, and preliminary results indicate that the contact resistance was very low. With typical Si/SiGe RITD congurations, the phonon spectra were found to be dominated by the phonon peaks of bulk Si. Of the Si/SiGe RITD structures that were measured, only those with a relatively thick Si1-xGex layer in the composite tunneling barrier and a high Ge content x = 0:6 produced phonon spectra in which the transverse acoustic (TA) phonon of the Si0:4Ge0:6 were observable, but the longitudinal acoustic (LA), longitudinal optical (LO) and transverse optical (TO) phonons of Si1-xGex were not observed. The energy of the TA phonon of Si0:4Ge0:6 in Si/SiGe RITDs grown on Si substrates was determined to be about 4+-1 meV higher than that measured using Esaki tunnel diodes. This increase is attributed to the compressive strain in the Si0:4Ge0:6 layer in the Si/SiGe RITDs.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2007