Spin splitting of X-related donor impurity states in an AlAs barrier
  We use magnetotunneling spectroscopy to observe the spin splitting of the ground state of an X-valley-related Si-donor impurity in an AlAs barrier. We determine the absolute magnitude of the effective Zeeman spin splitting factors of the impurity ground state to be g$_{I}$= 2.2 $\pm $ 0.1. We also investigate the spatial form of the electron wave function of the donor ground state, which is anisotropic in the growth plane. 
E. E. Vdovin, Yu. N. Khanin, L. Eaves, M. Henini, G. Hill