Elastic energy loss due to the reorientation of H around B in silicon

Measurements of elastic energy dissipation and elastic modulus have been carried out in Si:B before and after hydrogen incorporation by both iongun irradiation and plasma exposure. Experiments were performed at three widely separated frequencies (2.4, 13, and 32 kHz). Both types of H treated samples present a peak due to a thermally activated relaxation process at 130 K (2.4 kHz). The activation energies deduced from both the peak shift with frequency and the peak width have the same value, W = (0.22±0.01)eV. This indicates that the observed process is characterized by a single relaxations time, whose pre-exponential factor is t0 = (8±4x10- 14 )s. The value measured for the activation energy is in excellent agreement with the one estimated from infrared spectroscopy and logarithmic decrement measurements, and with the theoretical estimate for H trapped in bond-center position between neighboring Band 5i atoms. The absence of broadening of the dissipation peak demonstrates that the interaction between the boron trapping centers is still negligible at the B concentrations presently used (up to 6x10l9 atoms/cm3 ). Measurements on highly B doped samples H-treated by plasma exposure show, an additional peak at 210 K, whose rather unusual features will be illustrated.