Determination of spin- and valley-split energy levels in strained Si quantum wells

The energy spacing of spin- and valley-split energy levels in strained Si quantum wells is determined using tilted-magnetic-field Shubnikov - de Haas measurements. The effective Lande g-factor, g*, is determined both as a function of electron sheet concentration, ns, and Landau level occupation number, v. The value of g* is determined from the angle at which the longitudinal magnetoresistance minima of adjacent spin-split Landau levels are equal. For the coincidence of the v = 6 and v = 8 levels, g* increases from 2.9 ± 0.1 to 3.8 ± 0.2 as ns is decreased from 5.9 × 1011 cm-2 to 4.4 × 1011 cm-2 at T = 0.4 K. In the same sample, with fixed electron concentration of ns = 4.1 × 1011 cm-2, g* ≈ 3.5 for v ≳ 10, and oscillates between average values of 2.6 ± 0.1 and 4.2 ± 0.2, for lower values of v. The magnitude of the valley splittings has also been investigated; for a perpendicular magnetic field of ∼ 2.8 T, a splitting of 52 ± 11 μe is determined, which is several times smaller than values for Si inversion layers reported in the literature.