Electrically active defects introduced into Ge crystals co-doped with tin and phosphorus atoms by irradiation with 6 MeV electrons have been studied by means of transient capacitance techniques and ab-initio density functional modeling. It is shown that Sn atoms are effective traps for vacancies (V) in the irradiated Ge:Sn+P crystals. The electronic structure of Sn-V is unraveled on the basis of hybrid states from a Sn atom and a divacancy. Unlike the case for Si, Sn-V in Ge is not a donor. A hole trap with 0.19 eV activation energy for hole emission to the valence band is assigned to an acceptor level of the Sn-V complex. The Sn-V complex anneals out upon heat-treatments in the temperature range 50-100 °C. Its disappearance is accompanied by the formation of phosphorus-vacancy centers. © 2011 American Institute of Physics

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We have recently shown that Sn impurity atoms are effective traps for vacancies (V) in Ge:Sn crystals irradiated with MeV electrons at room temperature [V.P. Markevich et al., J. Appl. Phys. 109 (2011) 083705]. A hole trap with 0.19 eV activation energy for hole emission to the valence band (Eh) has been assigned to an acceptor level of the Sn-V complex. In the present work electrically active defects introduced into Ge:Sn+P crystals by irradiation with 6 MeV electrons and subsequent isochronal annealing in the temperature range 50-300 °C have been studied by means of transient capacitance techniques and ab-initio density functional modeling. It is found that the Sn-V complex anneals out upon heat-treatments in the temperature range 50-100 °C. Its disappearance is accompanied by the formation of vacancy-phosphorus (VP) centers. The disappearance of the VP defect upon thermal annealing in irradiated Sn-doped Ge crystals is accompanied by the effective formation of a defect which gives rise to a hole trap with Eh= 0.21 eV and is more thermally stable than other secondary radiation-induced defects in Ge:P samples. This defect is identified as tin-vacancy-phosphorus (SnVP) complex. It is suggested that the effective interaction of the VP centers with tin atoms and high thermal stability of the SnVP complex can result in suppression of transient enhanced diffusion of phosphorus atoms in Ge.

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Transformations of structural defects, the hydrogen state, and electrophysical properties of silicon treated in hydrogen plasma are studied. Treatment in plasma (150 o C) produces bands in Raman spectra at 2095 and 2129 cm -1 that are associated with scattering by Si-H vibrations. Subsequent heat treatment (275 o C) causes a band for gaseous molecular H 2 to appear at 4153 cm -1 . A comparison of Raman spectra and scanning probe microscopy results shows that hydrogenation forms defects (platelets) of average size 43 nm and surface density 6.5•10 9 cm -2 that are due to precipitation of H 2 and formation of Si-H bonds. Inclusions of average size 115 nm and surface density 1.7•10 9 cm -2 that are fi lled with molecular H 2 are observed after heat treatment. The concentration of free charge carriers remains constant after treatment in plasma and subsequent heat treatment.