Phonon-limited inversion layer electron mobility in extremely thin Si layer of silicon-on-insulator metal-oxide-semiconductor field-effect transistor

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Abstract
Phonon-limited inversion layer electron mobility in extremely thin (100) Si layers of silicon-on-insulator field-effect transistors has been studied at 300 K using a relaxation time approximation and a one-dimensional self-consistent calculation. For the Si layer thickness tSi of more than approximately 5 nm, the mobility behavior as a function of an effective vertical electric field is found to be almost identical with that of bulk Si inversion layers. For a thickness of less than that, however, the mobility behavior is considerably affected by the change in the electronic structures due to a confinement effect. As the Si layer thickness decreases, the phonon-limited electron mobility μph increases to a maximum at tSi of ∼3 nm and decreases monotonically. The increase in mobility results from the increase of the fraction of electrons in the lowest energy subband that has a higher mobility than other subbands. The mobility decrease in the extremely thin tSi region is attributed to the enhancement of phonon scattering rates caused by a reduction of the spatial widths of the subbands.