Abstract
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 density with increasing
[SiF4/He].