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:

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

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

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