Articles you may be interested inMobility enhancement effect in heavily doped junctionless nanowire silicon-on-insulator metal-oxidesemiconductor field-effect transistors Electron mobility in nanoscale silicon-on-insulator (SOI) layers with a doping concentration ranging from 2 Â 10 17 cm À3 to 1 Â 10 19 cm À3 is thoroughly studied. We observe that electron mobility in highly doped nanoscale extremely thin SOI (ETSOI) layers with thicknesses ranging from 5 to 11 nm is greater than electron mobility in bulk Si with the same doping concentration. Since no dopant ion exists in the oxides above and below ETSOI, the absence of ions close to the ETSOI layers effectively reduces the number of Coulomb centers that scatter carriers in the ETSOI layers. We show that the ratio of SOI thickness to the average distance between donor ions is critically important to understand the mobility enhancement in nanoscale ETSOI. It is demonstrated that mobility enhancement can be universally described as a function of the ratio described above. The findings of our study are indispensable in designing aggressively scaled SOI metal-oxidesemiconductor field-effect transistors.

Junctionless, or accumulation-mode, metal–oxide–semiconductor field-effect transistors (MOSFETs), where the channel and source/drain doping types are the same, have attracted growing interests because of their simpler fabrication processes. However, carrier transport properties, in particular, mobility characteristics, in the junctionless silicon-on-insulator (SOI) MOSFETs have been less studied. Although higher mobility in accumulation-mode SOI MOSFETs has been reported, the physical mechanisms of the higher mobility have not yet been clarified. In this work, the physical mechanisms of higher mobility in accumulation-mode MOSFETs have been investigated. We fabricated junctionless SOI MOSFETs with a channel doping concentration of 1×1017 cm-3 and an SOI body thickness of 48 nm whose mobility is greater than the bulk universal mobility in spite of the high doping concentration in the channel. The drain current consists of two components: one in the accumulation layer and the other in the SOI body. The mobility of each component is evaluated separately. As a result, it is revealed that the total mobility is the weighted mean of the two mobility components, where carrier concentration is the weight.

Understanding the dopant properties in heavily doped nanoscale semiconductors is essential to design nanoscale devices. We report the deionization or finite ionization energy of dopants in silicon (Si) nanofilms with dopant concentration (ND) of greater than 10(19) cm(-3), which is in contrast to the zero ionization energy (ED) in bulk Si at the same ND. From the comparison of experimentally observed and theoretically calculated ED, we attribute the deionization to the suppression of metal-insulator transition in highly doped nanoscale semiconductors in addition to the quantum confinement and the dielectric mismatch, which greatly increase ED in low-doped nanoscale semiconductors. Thus, for nanoscale transistors, ND should be higher than that estimated from bulk Si dopant properties in order to reduce their resistivity by the metal-insulator transition.

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