Electron effective mass enhancement in ultrathin gate-oxide Si-MOSFETs

The effective mass (m*) of two-dimensional electrons in Si-MOSFETs, obtained from measurements of the thermal damping of Shubnikov-de Haas oscillations, has been studied as a function of electron density for samples with physical gate-oxide thicknesses of 4.7 nm and 3.1 nm. The electron-electron interaction-driven enhancement of m* in both thin-oxide samples is well described by m*/mb = 0.96 + γrs, where mb is the bare band mass within the plane of confinement, and γ is a constant. Although the results from both sets of samples are in good quantitative agreement with previous experiments on thicker-oxide MOSFETs, a small but significant difference in γ between the thin-oxide samples was observed. We speculate that the experiments could provide evidence of a reduction in the mass enhancement due to the screening effect of the gate. The response of m* to changes in the confining potential for the two-dimensional electron system is also investigated. © 2005 American Institute of Physics.