Arsenic incorporation in MBE grown Hg1−xCdxTe

The p-type doping of Hg1−xCdxTe (MCT) has proven to be a significant challenge in present day MCT-based detector technology. One of the most promising acceptor candidates, arsenic, behaves as an amphoteric dopant which can be activated as an acceptor during Hg-rich, low temperature annealing of as-grown molecular beam epitaxy (MBE) samples. This study focuses on developing an understanding of the microscopic behavior of arsenic incorporation during MBE growth. In particular, the question of whether arsenic incorporates as individual As atoms, as As2 dimers, or as As4 tetramers is addressed for MBE growth with an As4 source. A quasithermodynamical model is employed to describe the MCT growth and As incorporation, with parameters fitted to an extensive database of samples grown at the Microphysics Laboratory. The best fits for growth temperatures between 175 and 185°C are obtained for arsenic incorporation as As4 or possibly as As4 clusters, with lower probabilities for As2 and individual As atoms. Based on these results, we investigate the relaxed atomic configurations of As4 and As2 in bulk HgTe by ab initio total energy calculations. The calculations are performed in the pseudopotential density-functional framework within the local density approximation, employing supercells with periodic boundary conditions. The lattice distortions due to As4 and As2 in bulk HgTe are predicted to be modest due to the small size of these arsenic clusters.