Valley splitting and valley degeneracy in n-type silicon (110) inversion layers

The magneto-quantum transport phenomena of silicon (110) n-type inversion layers directly reveal the presence of two types of electrons in i = O and O' electric subband states from their respective quantum oscillations. While the higher i = O' states are occupied by only about 6% of the total electron concentration in our samples, the i = O electrons populate two valley pairs each, the level ladders of which are shifted in energy by less than the Landau splitting in the range where quantum oscillations are observed. We propose this effect to originate from a slight misorientation (Δθ < 0.5°) of the surfaces investigated with respect to the (110) axis. Hence, increasing the gate voltage in a quantizing magnetic field all four i = O valleys are alternatingly occupied in pairs with increasing Landau quantum number in our (110) surfaces contrary to former conclusions on samples with comparable properties. The effect of the magnitude of Δθ on the resulting magneto-quantum oscillations is unimportant for 0 < Δθ ? 0.5° as a result of energy minimization for the total electron system.