3.4.3 Effective Masses in Strained SiGe

To take into account effects beyond the linear deformation-potential theory the model of Rieger and Vogl [61] is used for the substrate orientation $[001]$. This model gives the effective masses versus Ge mole compositions in the active layer and the substrate:

$$m^{*}(x,y) =\begin{pmatrix}1, & (x-y), & (x-y)^{2} \end{pmatrix}\mathbf{W}\begin{pmatrix}1 \\ (x+y)\end{pmatrix}$$ (3.64)

where $\mathbf{W}$ contains parameterized transverse and longitudinal effective masses for the perpendicular and parallel $X$ valleys, and $x$ and $y$ denote the Ge mole fractions of the active layer and the substrate, respectively.

For substrate orientations different from $[001]$ a linear interpolation

$$m^{*}_{SiGe}=m^{*}_{Si}(1-x)+m^{*}_{Ge}x.$$ (3.65)

is used for the effective masses in the active layer. S. Smirnov: