Effects of hydrogen partial pressure on the structure and properties of sputtered silicon layers

Hydrogenated silicon films were deposited by RF sputtering with various hyd rogen partial pressures. The samples were examined by infrared absorption s pectroscopy, transmission electron microscopy and optical absorption techni ques, in addition to dark conductivity measurements. For low hydrogen press ure ratios ( less than or equal to 20%), the deposited hydrogenated films w ere completely amorphous, but they increasingly crystallize for increasingl y higher ratio of hydrogen pressure. Beside an appropriate value of the opt ical band gap, the conductivity improved by more than eight orders of magni tude, from similar to 10(-11) Omega(-1) cm(-1) for the amorphous phase to s imilar to 10(-3) Omega(-1) cm-l for the most crystalline one. This latter v alue and the corresponding low activation energy (0.13 eV) are explained in terms of a thermally-assisted tunnelling process. (C) 1999 Elsevier Scienc e S.A. All rights reserved.