ACOUSTIC ATTENUATION BY SHALLOW DONORS IN GERMANIUM IN A MAGNETIC FIELD

Abstract
We have reported on the experimental results of the acoustic attenuation at about 1 GHz in antimony doped germanium in a magnetic field and at liquid helium temperatures, and that the magnetic field effect on the acoustic attenuation (MFEAA) is far larger than that expected from the present theories. Further experiments were carried out to measure the MFEAA in n-type (antimony, phosphorous or arsenic doped) germanium in the higher frequency region (2-3 GHz) and in other configurations. Some interesting results were obtained and these are summarized as follows : (1) When the magnetic field [MATH] was applied along the [100] axis and the wave vector [MATH] and the polarization vector [MATH] were along the [110] axis (in this configuration, the degeneracy of the four-pair conduction band minima in the k-space is not removed, so only the shrinkage effect of the donor wave function is expected as an effect of the magnetic field on the ground states of the bound donor electrons) the attenuation decreased with magnetic field and showed a minimum at 27 kG, then, increased with field up to 60 kG. The position of the minimum point is independent of the donor concentration or of the temperature or of the frequency. Such a behavior can not be explained by the present theories. (2) From the experimental results of MFEAA an phosphorus doped germanium for the configuration of [MATH][111] axis at 3.35 GHz, it was found that the effective Bohr radius a* increases with temperature. (3) From the experimental results of MFEAA in arsenic doped germanium for the configuration of [MATH][111] axis at 3.35 GHz, it was found that the behavior is not explained using a reasonable value for the effective Bohr radius a*.