Hopping and Tunnelling of H(D) in Semiconductors

The dynamics of H and D in p-type Si:B and GaAs:Zn in n-type Si:P and GaAs:Si, have been studied by acoustic spectroscopy measurements in the temperature range 1 K-550 K and at frequencies between 1 and 30 kHz. By combining the data from anelastic relaxation and from the dichroism decay, the relaxation rates of the H-B pair are obtained over 11 decades and there are clear indications of a deviation at low temperature from the classical dependence. However, no conclusions can be drawn at present on the mechanism governing the H(D) transitions. The complete absence of relaxation effects in Si:P may confirm that H occupies backbonding sites in this system. In deuterated GaAs:Zn, a new peak is observed at 20 K. This peak is much broader than a single-time Debye peak, and is due to a species performing unexpectedly high transition rates: more than 15-20 orders of magnitude higher than in all the other semiconductors measured so far. This species has been identified as the D-Zn complex. The analysis of data demonstrates that the nature of the relaxation is strongly quantistic. Measurements on GaAs:Si-D suggest that the energy barrier separating the four D antibonding sites around Si may be rather high.