First-principles study of arsenic impurity clusters in molecular beam epitaxy (MBE) grown HgCdTe

The understanding of the microstructures of the arsenic tetramer (Ast), dimer (Asd), and singlet (Ass) of HgCdTe is important to explain the high electrical compensation of molecular beam epitaxy (MBE) samples and the conversion to p-type behavior. The stable configurations were obtained from the first-principles calculations for the arsenic cluster defects [Asn (n=1, 2, and 4)] in as-grown HgCdTe. According to the defect formation energies calculated under Te-rich conditions, the most probable configurations of Ast, Asd, and Ass have been established. For the optimized Ast and Asd the energy is favorable to combine in a nearest neighboring mercury vacancy (VHg), and the corresponding configurations can be used to explain the self-compensated n-type characteristics in as-grown materials. Ast is likely to be more abundant than Asd in as-grown materials, but arsenic atoms are more strongly bounded in Ast than in Asd, thus more substantial activation energy is needed for Ast than that for Asd. The atomic relaxations as well as the structural stability of the arsenic defects have also been investigated.