Wide Electrical Tunability of the Valley Splitting in a Doubly Gated Silicon-on-Insulator Quantum Well

The valley splitting of 2D electrons in doubly gated silicon-on-insulator quantum wells is studied by low temperature transport measurements under magnetic fields. At the buried thermal-oxide SiO2 interface, the valley splitting increases as a function of the electrostatic bias δn = nB - nF (where nB and nF are electron densities contributed by back and front gates, respectively) and reaches values as high as 6.3 meV, independent of the total carrier concentration of the channel. We show that δn tunes the square of the wave function modulus at the interface and its penetration into the barrier, both of which are key quantities in a theory describing interface-induced valley splitting, and is therefore the natural experimental parameter to manipulate valleys in 2D silicon systems. At the front interface, made of a thin "high-k" dielectric, a smaller valley splitting is observed, adding further options to tune the valley splitting within a single device.