STRUCTURAL AND OPTICAL PROPERTIES OF NANOCRYSTALLINE SILICON FILMS DEPOSITED AT 150°C

Abstract

Nanocrystalline silicon (nc-Si) films were deposited by plasma-enhanced chemical vapor deposition from a SiH 4- H 2 gas mixture. The structural and optical properties of nc-Si films were examined by changing the flow rates of a H 2 gas or a SiF 4 gas diluted by He. The structural change from an amorphous to a nanocrystalline phase was found at H 2 flow rate ([ H 2]) higher than 3 sccm under [ SiF 4/ He ] = 0 sccm and/or by adding SiF 4/ He under [ H 2] = 0 sccm . However, under [ H 2] = 3 sccm, the maximum crystallinity (crystalline volume fraction, ρ) was observed at around [ SiF 4/ He ] = 2 sccm . The photoluminescence exhibited two peaks at around 1.7 eV and 2.2 - 2.3 eV. The first 1.7-eV-peak may be related to nanocrystallites in nc-Si films and the origin of another 2.2 - 2.3-eV-peak is not clear. Thus, hydrogen and fluorine appear to play different role in the crystallization process. In addition, under [ H 2] = 0 sccm , we found a close correlation among the increases in the ρ and the average grain size values and the SiH 2 density with increasing [ SiF 4/ He ].