Impurity-induced surface acoustic wave attenuation in doped amorphous GeH thin films

The technique of surface acoustic wave (SAW) has been applied to doped amorphous GeH films to gain information on the nature of defects. The attenuation of SAW of 300 MHz and 1.5 GHz has been measured in sputtered films of a-GeH doped with P or B at temperatures between 0.5 and 475 K. Sound velocity measurements are also made. A strong absorption maximum at low temperature is observed in a-Ge(H,P) and a-Ge(H,B) films. Distinct effects of annealing on the attenuation and velocity of SAW are observed. These impurity induced features are discussed in the light of acoustoelectric interaction. It is interesting to observe that a-Ge(H,B) film seems to have tunneling states characteristic of glasses.