The change in the sound velocity in Sb-doped Ge

The authors have measured the change Delta v in the sound velocity in Sb-doped Ge over a concentration N range 3.1*10 16 -1.6*10 18 cm -3 and a temperature range 1.8-40 K. The stress dependence of Delta v has been also measured in a limited concentration range near the critical concentration N c for the metal-nonmetal transition over a temperature range 2.3-4.2 K. The density of states for N>10 17 cm -3 has been derived from fitting to Delta v under the assumption that the electron-phonon coupling in the impurity band is identical with that in the conduction band. The stress dependence is qualitatively explained using the density of states obtained. The relaxation time in the sound attenuation near N c is found to be sensitive to the stress. The metal-nonmetal transition in this system occurs in the impurity band.