Anisotropic spatial structure of deep acceptor states in GaAs and GaP

Cross-sectional scanning tunneling microscopy is used to identify the origin of the anisotropic electronic structure of acceptor states in III-V semiconductors. The density of states introduced by a hole bound to an individual Cd acceptor in GaP is spatially mapped at room temperature. Similar to the Mn hole wave function in GaAs, we found a highly anisotropic, crosslike shape of the hole bound to Cd both at the GaP(110) and the GaP(1 (1) over bar0) orthogonal cleavage planes. The experimentally observed similarity of the symmetry properties of Mn:GaAs to Cd:GaP shows that the anisotropic structure of acceptor states in zinc-blende III-V compounds is determined by the cubic symmetry of the host crystal. Nevertheless, the weak spin-orbit interaction in GaP leads to a slight modification of the Cd bound-hole wave function relative to that of Mn in GaAs. In addition to the anisotropic angular structure of the d-like spherical harmonic of the wave function, which dominates the appearance of the hole ground state far from the ionic core, the admixture of g-like and higher order spherical harmonics is identified at the sides of the Cd hole wave function. The experimentally obtained results agree with both atomistic tight-binding and envelope-function effective-mass theoretical models