Spin-orbit splittings in Si/SiGe quantum wells: from ideal Si membranes to realistic heterostructures

We present a calculation of the wavevector-dependent subband level splitting from spin-orbit coupling in Si/SiGe quantum wells. We first use the effective-mass approach, where the splittings are parameterized by separating contributions from the Rashba and Dresselhaus terms. We then determine the inversion asymmetry parameters by fitting tight-binding numerical results obtained using the quantitative nanoelectronic modeling tool, NEMO-3D. We describe the relevant coefficients as a function of applied electric field and well width in our numerical simulations. Symmetry arguments can also predict the behavior, and an extensive analysis is also presented in this work. Using vast computational resources, we treat alloy disorder at the atomistic scale. We obtain first-time results for realistic Si/SiGe heterostructures. Our numerical data are in very good agreement with experimental results, both qualitatively and quantitatively. We conclude that effects of alloy disorder have a crucial influence on the spin-orbit parameters.