Diffusion Mechanism for Arsenic in Intrinsic and Extrinsic Conditions in HgCdTe

Abstract

Due to its low diffusivity and high activation rate, arsenic has become the dopant of choice in p/n HgCdTe high operating temperature technology. Its diffusion mechanism, however, remains imprecise. In this work, arsenic diffusion was studied in molecular beam epitaxy HgCdTe structures consisting of alternatively As-doped and intrinsic layers grown on a CdZnTe substrate. The diffusion coefficient of As was extracted from secondary ion mass spectroscopy concentration profiles. Annealings were performed for different temperatures, mercury partial pressures (P _Hg), annealing times and cadmium atomic fractions. Fermi-level effect on diffusion was observed, indicating extrinsic conditions for diffusion at high As concentration. Based on the variation of As diffusivity with P _Hg and As concentration, we propose that As diffusion occurs on both II and VI sublattices. Our results are consistent with the fact that As_VI diffusion is assisted by the Te interstitial, introducing donor levels in the bandgap, while As_II diffusion is assisted by the cation vacancy.