Evidence for the void size related IR absorption frequency shifts in hydrogenated amorphous germanium films

Hydrogenated amorphous germanium alloys (a-Ge:H) have been prepared by plas ma enhanced chemical vapor deposition at a substrate temperature of 200 deg rees C. The films tend to oxidize as soon as they are taken out from the ch amber and exposed to air. The oxidation process is found to follow a percol ation channel formed by a continuous linkage of large voids that is evidenc ed by the observation of the decline of the intensity of Ge-H stretching mo de at 1980 cm(-1) to zero while the other peak at 1890 cm(-1) does not chan ge. This means that the peak at 1980 cm(-1) corresponds to the Ge-H stretch ing mode in large voids while that at 1890 cm(-1) corresponds to Ge-H stret ching mode in isolated small voids. Thus, the frequency shifts of the stret ching mode should arise from the difference of the void size where Ge-H bon ds are situated. (C) 1999 Elsevier Science Ltd. All rights reserved.