Charge manipulation and imaging of the Mn acceptor state in GaAs by   Cross-sectional Scanning Tunneling Microscopy
  An individual Mn acceptor in GaAs is mapped by Cross-sectional Scanning Tunneling Microscopy (X-STM) at room temperature and a strongly anisotropic shape of the acceptor state is observed. An acceptor state manifests itself as a cross-like feature which we attribute to a valence hole weakly bound to the Mn ion forming the (Mn$^{2+}3d^5+hole$) complex. We propose that the observed anisotropy of the Mn acceptor wave-function is due to the d-wave present in the acceptor ground state. 
A.M. Yakunin, A.Yu. Silov, P.M. Koenraad, J.H. Wolter, W. Van Roy, J.   De Boeck