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).