  We fabricated silicon metal-oxide-semiconductor field effect transistors
where an additional sodium-doped layer was incorporated into the oxide to
create potential fluctuations at the Si-SiO2 interface. The amplitude of these
fluctuations is controlled by both the density of ions in the oxide and their
position relative to the Si-SiO2 interface. Owing to the high mobility of the
ions at room temperature, it is possible to move them with the application of a
suitable electric field. We show that, in this configuration, such a device can
be used to control both the disorder and the electron-electron interaction
strength at the Si-SiO2 interface.
