Spin splitting of X-valley-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 gI=2.2±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.