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

The understanding of the microstructures of the arsenic tetramer ( As t ) , dimer ( As d ) , and singlet ( As s ) 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 [ As n ( 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 As t , As d , and As s have been established. For the optimized As t and As d the energy is favorable to combine in a nearest neighboring mercury vacancy ( V Hg ) , and the corresponding configurations can be used to explain the self-compensated n -type characteristics in as-grown materials. As t is likely to be more abundant than As d in as-grown materials, but arsenic atoms are more strongly bounded in As t than in As d , thus more substantial activation energy is needed for As t than that for As d . The atomic relaxations as well as the structural stability of the arsenic defects have also been investigated.