COPPER DIFFUSION IN AMORPHOUS-GERMANIUM

The diffusion coefficient of copper in amorphous germanium is estimate d to be larger than 3 x 10(-11) cm(2) s(-1) and the solubility to be s imilar to 7 x 10(18) cm(-3) at 200 degrees C as determined from second ary mass spectrometry. The observed solubility Limit is more than eigh t orders of magnitude greater than that in crystalline germanium and t he enthalpy of a solution of copper in amorphous germanium is estimate d to be as low as 0.05 eV in the range of 20-200 degrees C. Copper is observed to diffuse more readily in amorphous germanium than in amorph ous silicon, with an activation enthalpy as low as similar to 0.5 eV i n the range of 20-200 degrees C. Interstitial diffusion is assumed to prevail and the trapping enthalpy of defects retarding the motion is f ound to be significantly lower in amorphous germanium (0.25 +/- 0.15 e V) compared to that in amorphous silicon (similar to 0.8 eV). (C) 1998 American Vacuum Society. [S0734-2101(98)00204-8].