Properties of Silicon Crystals Doped with Zirconium or Hafnium

Zr- and Hf-doped crystals prepared by the floating zone technique are investigated with DLTS measurements. For doping concentrations near 1 × 1020 cm−3 in the melt electrically active concentrations of about 1 × 1012 cm−3 were achieved for n-and p-type crystals. On account of the energy level arrangement these concentrations can be interpreted by the segregation coefficients k = 1.6 × 10−8 (Zr) and k = 1 × 10−8 (Hf). For both doping metals similar energy levels and annealing properties are detected. Three levels at Ec − 0.14 (0.10) eV, Ec − 0.41 (0.39) eV, and Ev + 0.32 (0.32) eV can be explained as different charge states Zr− (Hf−), Zr+ (Hf+), Zr++ (Hf++) of the same impurity center. In the surface regions of the crystals some other defect levels E0 up to E4 caused by unknown defect reactions are also observed. For the real impurity center M = Zr(Hf) near T = 280 (320) °C at first a reaction roughly described by M → E2(M), E3(M) and then the reaction E2(M), E3(M) → M can be detected in n-type Si. Additionally for n-type crystals with Pd-contacts near T = 200 °C the reaction E0(M), E1(M) → M, E2(M) is observed for both doping metals.