Grain boundary defects in RTCVD polycrystalline silicon for solar cells

The electrical and optical properties of polycrystalline silicon films are dominated by grain-boundary defects. It is therefore of particular interest to obtain columnar grain growth during the deposition process. In this wor k, we studied the properties of RTCVD deposited polycrystalline silicon fil ms suitable for solar cell production. The effect of substrate temperature on texture and paramagnetically active defects of polycrystalline Si-films deposited on mono-Si substrate were studied in the temperature range 870-12 40 degreesC. Preferential grain orientation is found for all polycrystallin e films in the whole range of depositing temperature, with the < 110 > orie ntation as the main texture component. The volume fraction of this texture component reaches a maximum for 1030-1100 degreesC, while weak < 311 > and < 111 > components clearly display slight enhancement for 960 degreesC. For deposition temperatures above 1100-1240 degreesC the density of the main < 110 > -texture component diminishes in favour of isotropic grain orientati ons. The concentration of paramagnetically active dangling bonds matches wi th the volume fraction of < 110 > oriented grains. It is shown that the spr eading in growth direction causes the formation of highly defective grain b oundary regions that are the main source of dangling bonds. (C) 2001 Elsevi er Science Ltd. All rights reserved.