Impurity Dopant Incorporation and Diffusion during Molecular Beam Epitaxial Growth of IV–VI Semiconductors

Abstract

, , and single crystal films were grown on at 620°–720°K and 10−9 Torr by coevaporation of the stoichiometric binary compounds and the dopant elements from separate sources. Molecular incident fluxes measured with a quartz crystal monitor usually agreed with those calculated from vapor pressure data to within 20%. Unintentionally doped films had carrier concentrations in the 1016–1017 cm−3range. n and p doping were achievable by stoichiometry adjustment using coevaporated Pb and Te (or Se), respectively; but only ≈0.1% of each became incorporated: the remainder surface‐segregated (Pb) or reevaporated (Te,Se). Conversely, of incident Bi and Tl became incorporated as n and p dopant, respectively, to levels >1019 cm−3, most likely by substituting for Pb or Sn and displacing it to the growth surface; except that Bi in the selenide (and Sb in both) showed less incorporation as dopant at >1018 cm−3, most likely due to compensation. behaved as Bi in the telluride and was found to sublime molecularly according to . SIMS depth profiling of grown abrupt dopant steps showed high‐concentration diffusion coefficients of Bi and Tl in at 650°K and of Tl in at 620°K to be , respectively; but much faster diffusion (>10−10 cm2/sec) of Tl in the selenide occurred up to . Similar low‐concentration fast diffusion caused carrier concentrations of undoped telluride films below layers doped with Bi or to be shifted by toward n‐type and toward p‐type, respectively; the latter and possibly also the former shift was due to equalization of dopant‐perturbed stoichiometry deviation rather than to fast‐diffusing Bi. Excellent junction profile control may be obtained with these impurity dopants provided that the fast‐diffusing components are appropriately compensated for in junction design.