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

Nanocrystalline silicon (nc-Si) films were deposited by plasma-enhanced chemical vapor deposition from a SiH4-H2 gas mixture. The structural and optical properties of nc-Si films were examined by changing the flow rates of a H2 gas or a SiF4 gas diluted by He. The structural change from an amorphous to a nanocrystalline phase was found at H2 flow rate ([H2]) higher than 3 sccm under [SiF4/He] = 0 sccm and/or by adding SiF4/He under [H2] = 0 sccm. However, under [H2] = 3 sccm, the maximum crystallinity (crystalline volume fraction, ρ) was observed at around [SiF4/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 [H2] = 0 sccm, we found a close correlation among the increases in the ρ and the average grain size values and the SiH2 d...