Temperature dependence of local structure of Ge impurity in Si (001) thin film probed by multiple-scattering XAFS

Abstract

The local structure of dilute Ge impurity in Si thin film has been studied by grazing incidence fluorescence XAFS in the temperature region of 20 ∼ 300 K. Multiple-scattering XAFS (MS-XAFS) data analysis is used to fit the local structures around Ge atoms from the first to third coordination shells for the Ge0.006Si0.994 thin film. The results indicate that the bond length RGe–Si of the first, second and third Ge-Si shell is 2.38, 3.83 and 4.49 Å for the Ge0.006Si0.994 thin film, respectively. The RGe–Si of the first Ge–Si shell in the Ge0.006Si0.994 thin film is 0.03 larger than that of the first Si–Si shell in Si crystal, and the RGe–Si of the second and third Ge–Si shells in the Ge0.006Si0.994 thin film are almost equal to those of the corresponding Si–Si shells in Si crystal. These results imply that the local lattice deformation exists in the first nearest neighbor around Ge atoms and the lattice distortion relieves in the second and third Ge–Si shells for the Ge0.006Si0.994 thin film. Furthermore, the results show that the Debye-Waller factor σ12 of the first Ge–Si shell of the Ge0.006Si0.994 thin film increases slightly from 0.0018 to 0.0020 Å2 in the temperature region between 20 and 100 K, and rises strongly to 0.0040 Å2 at 300 K. The bond angles θGe–Si–Si at all temperatures are about 108.1°, which is close to the value of tetragonal network of 109.47°. The bond angle variation ΔθGe–Si–Si is about ±3.4°, ±3.5° and ±5.0° at the temperatures of 20, 100 and 300 K, respectively, indicating a weak tetragonal distortion around the Ge atoms in the Ge0.006Si0.994 thin film.