Electron mobility in ultrathin silicon-on-insulator layers at 4.2 K

Low temperature mobility measurements of silicon-on-insulator (SOI) metal-oxidefield-effect-transistors are reported. The batch of devices fabricated in this work includes both ultrathin and thick devices for which the SOI film thicknesses are in the ranges of 10–15 nm and 56–61 nm, respectively. The 4.2 K peak mobility of the thick devices is 1.9 m²/V s. The ultrathin devices show mobility degradation at low electron densities where the mobility is also observed to decrease with decreasing the SOI film thickness. The peak mobilities of these devices are in the range of 1.35–1.57 m²/V s. Numerical calculations show that ultrathin devices are in the limit where the electrons are confined by the quantum well defined by gate oxide and buried oxide, which is interpreted to lead to the observed mobility degradation.