A first principles study on the adsorbate-adsorbate interactions on the CdTe(111) surface with Cd, Te, Zn, and Se adatoms
The study of adsorbate-adsorbate interactions is essential to understanding early crystal growth dynamics. Here, we employ planewave density functional theory to study the binary adatom pair interactions between Cd-Cd, Te-Te, Zn-Zn, Se-Se, Cd-Te, Cd-Se, Cd-Zn, Te-Se, Te-Zn, and Se-Zn adatom pairs on two CdTe(111) surfaces. An analysis of the interaction energies between binary adatom pairs suggests repulsive interactions are common regardless of the relative distance between adatoms. For the CdTe(111)A surface, attractive interactions occur between neighboring chalcogen (i.e., Te and Se) and Group 12 (i.e., Cd and Zn) adatom pairs. For the CdTe(111)B surface, attractive interactions occur between neighboring Group 12 adatoms forming a surface dimer configuration. Furthermore, the formation energy of an adatom pair is decomposed in terms of the electronic, elastic, and adatom binding contributions. For smaller interatomic distances between the adatoms, the formation energy is primarily a function of the electronic interactions, with null contributions from the elastic and adatom binding interactions for Group 12-containing pairs. Because of the less favorable electronic interactions for larger interatomic distances between the adatoms, the formation energies are typically more positive. Lastly, neighboring adatoms significantly increase the barriers of migration on the CdTe(111)A surface relative to unary adatoms for the top-to-fcc and fcc-to-fcc sites, while the migration barriers on the CdTe(111)B surface only increases for the fcc-to-fcc migration of chalcogen species. From this analysis, we illustrate the role of adatom interactions during the early stages of the surface nucleation processes on CdTe(111) thin films.