Ab Initio Studies of the Unreconstructed Polar CdTe (111) Surface

Ab initio electronic structure calculations were carried out for bulk cadmium telluride (CdTe) and the unreconstructed CdTe polar (111) Cd-terminated and ( $$ \bar{1}\bar{1}\bar{1} $$ ) Te-terminated surfaces. The hybrid functional for the exchange and correlation potential improves the overall description of the electronic structure of bulk CdTe, by lowering Cd 4d states and hence reducing the Cd 4d–Te 5p hybridization. The Cd–Te interlayer distance of the Cd-terminated surface exhibits a dramatic contraction in contrast with the expansion of the Te-terminated surface, and the surface relaxations decrease as the slab thickness increases. The underlying mechanism of the convergence of the electrostatic potential energy, work function, and electric dipole moment of the polar surfaces as a function of slab thickness is surface electron rearrangement leading to charge transfer from the Te- to the Cd-terminated surfaces. The surface electric polarization induces an internal electric field in the slab, which in turn tilts the bands of the slab double layers, thus rendering the surface layers metallic. The electric field decreases with increasing slab thickness due to convergence of the difference of electrostatic potentials between the Cd- and Te-terminated surfaces.