Density dependence of electron mobility in the accumulation mode for fully depleted SOI films

The electron mobility $\mu_{\mathrm{eff}}$ in the accumulation mode is investigated for undepleted and fully depleted double-gate $n^+$–$n$–$n^+$ silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFET). To determine the range of possible values of the mobility and the dominant scattering mechanisms in thin-film structures, it is proposed that the field dependence of the mobility $\mu_{\mathrm{eff}}$ be replaced with the dependence on the density $N_e$ of induced charge carriers. It is shown that the dependences $\mu_{\mathrm{eff}}(N_e)$ can be approximated by the power functions $\mu_{\mathrm{eff}}(N_e)\propto N_e^{-n}$, where the exponent $n$ is determined by the chargecarrier scattering mechanism as in the mobility field dependence. The values of the exponent $n$ in the dependences $\mu_{\mathrm{eff}}(N_e)$ are determined when the SOI-film mode near one of its surfaces varies from inversion to accumulation. The obtained results are explained from the viewpoint of the electron-density redistribution over the SOI-film thickness and changes in the scattering mechanisms.