Computation of the Stark effect in P impurity states in silicon

We compute within the effective-mass theory and without adjustable parameters the Stark effect for shallow P donors in Si with anisotropic band structure. Valley-orbit coupling is taken into account in a nonperturbative way and scattering effects of the impurity core are included to properly describe low-lying impurity states. The ground-state energy slightly decreases with increasing electric field up to a critical value ${E}_{\mathit{cr}}\ensuremath{\sim}25\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{cm}$, at which the donor can be ionized by tunneling due to a field-induced mixing of the ``$1s$-like'' singlet ground state with a ``$2{p}_{0}$-like'' excited state in zero field. The resulting ground-state wave function at high field extends significantly outside the potential barrier surrounding the impurity. Calculations of the hyperfine splitting and of the $A$-shell superhyperfine coupling constants as a function of the electric field complete the work.