Electron mobility enhancement in nanoscale silicon-on-insulator diffusion layers with high doping concentration of greater than 1 10¹⁸ × cm^-3 and silicon-on-insulator thickness of less than 10 nm

Electron mobility in nanoscale silicon-on-insulator (SOI) layers with a doping concentration ranging from 2 × 10¹⁷ cm^-3 to 1 × 10¹⁹ cm^-3 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-oxide-semiconductor field-effect transistors.