Copper diffusion in amorphous germanium

The diffusion coefficient of copper in amorphous germanium is estimated to be larger than 3 × 10-11 cm2 s-1 and the solubility to be ∼7 × 1018 cm-3 at 200°C as determined from secondary mass spectrometry. The observed solubility limit is more than eight orders of magnitude greater than that in crystalline germanium and the enthalpy of a solution of copper in amorphous germanium is estimated to be as low as 0.05 eV in the range of 20-200°C. Copper is observed to diffuse more readily in amorphous germanium than in amorphous silicon, with an activation enthalpy as low as ∼0.5 eV in the range of 20-200°C. Interstitial diffusion is assumed to prevail and the trapping enthalpy of defects retarding the motion is found to be significantly lower in amorphous germanium (0.25±0.15 eV) compared to that in amorphous silicon (∼0.8 eV). © 1998 American Vacuum Society.