TRANSPORT-PROPERTIES OF HG1-XZNXSE AND HG1-XMNXSE DOPED WITH FE RESONANT DONORS

We present here a,study of the influence of iron doping on transport a nd magnetotransport properties of HgSe-based narrow-gap semiconducting mixed crystals, namely Hg1-xZnxSe (x less than or equal to 0.072) and Hg1-xMnxSe(x less than or equal to 0.13). The crystals were grown by the Bridgman method. Measurements were performed in the temperature ra nge 1,7-300 K in magnetic fields up to 6 T. For both systems, the elec tron concentration as a function of increasing concentration of Fe dop ants changes in a similar way: it rises proportionally below a certain Fe donor concentration n(Fe) (which depends on the mole fraction x o f mixed crystal) and then reaches a constant value (which also depends on x). The electron mobility in samples with n(Fe) > n(Fe) shows ano malously high values, similarly to the case of HgSe:Fe studied earlier . We interpret the observed phenomena by assuming that iron dopants cr eate, in the compounds investigated, a resonant donor state with an en ergy level degenerate with the conduction band continuum. For n(Fe) > n(Fe) the system of Fe donors is only partially occupied by electrons , i.e., Fe2+ neutral donors and Fe3+ singly ionized donors coexist res ulting in a mixed valence regime. The Coulomb repulsion between the el ectrons localized on donors leads to a correlation of their positions and results in a dramatic reduction of the scattering rate by ionized impurity potentials. The analysis of the mobility (in the case of Hg1- xMnxSe also of the Dingle temperature) in terms of the scattering from ionized centers (with the possible spatial correlation of impurity ch arges taken into account) and the alloy scattering (in the case of Hg1 -xMnxSe also spin-dependent scattering) leads to a fair agreement betw een the measured data and the theoretical description. The lack of any dependence of the electron concentration upon the level of iron dopin g in the mixed valence regime (when the Fermi level is pinned to the i ron state) enabled us to determine the position of the Fe level as a f unction of the Zn or Mn mole fraction x. This, in turn, made it possib le to estimate the re and re band offsets (denoted W and V, respective ly) between HgSe and MnSe and between HgSe and ZnSe. The values determ ined by us are, in the Hg1-xZnxSe system W = -0.5 eV and V = 2.6 eV, a nd in the case of the Hg1-xMnxSe system W = -1.2 eV and V = 3 eV. More over, it is noted that even weak Fe doping (corresponding to n(Fe) < n (Fe)) can lead to a substantial improvement of electrical properties of the compounds studied by us. This is particularly clearly seen for Hg1-xZnxSe.