Precise arsenic doping of HgCdTe by MBE and effects on compositional interdiffusion

Characterization data are presented for arsenic-doped Hg1-xCdxTe epilayers, grown on CdZnTe substrates by molecular beam epitaxy. Arsenic incorporation is influenced both by the cracker-cell bulk temperature (As flux) and by the substrate surface temperature. An Arrhenius-type equation can be used to fit the As incorporation data, yielding characteristic energies of 1.54 and 6.61 eV for the As cell and HgCdTe surface temperatures, respectively, independent of alloy fraction. This relation allows significantly improved predictability and control in the As doping concentration. The effect of growth temperature on As incorporation is demonstrated using a multilayer test structure with composition stepped in a sequence, with x = 0.6, 0.45, 0.3, 0.2, of n-type material, followed by the reverse sequence of As-doped material, with the As cell temperature held constant. Secondary ion mass spectroscopy profiles of this layer again indicate the strong As incorporation dependence on growth temperature. Composition profiles for as-grown and annealed pieces of the multilayer sample show greater interdiffusion for the As-doped region as compared to the undoped region, which is attributed to the Fermi-level enhancement effect.