Abstract
We have studied the origin of photoluminescence (PL) from hydrogenated nanocrystalline silicon (nc-Si:H) films produced by a plasma-enhanced chemical vapor deposition technique using SiF
4/SiH
4/H
2 gas mixtures. The nc-Si:H films were characterized using X-ray diffraction, infrared, Raman spectroscopy, optical absorption and stress, and were examined for PL by varying the deposition temperature (
T
d) under two different hydrogen flow rate ([H
2]) conditions. The PL exhibited two peaks at around 1.7–1.75 and 2.2–2.3
eV. The peak energy,
E
PL, of the 1.7–1.75-eV PL band was found to shift as
T
d or [H
2] changes. It was found that the decrease in
T
d acts to decrease the average grain size, 〈
δ〉, and to increase both the optical band gap,
E
g
opt
, and the
E
PL values. By contrast, the increase in [H
2] decreased the 〈
δ〉 value, while increased the values of
E
g
opt
and
E
PL. Thus, as either
T
d decreases or [H
2] increases, it is found that a decrease in 〈
δ〉 corresponds well with increases in
E
g
opt
and
E
PL. As a consequence, it was suggested that an increase in
E
PL of the 1.7–1.75-eV PL band can be connected with an increase in
E
g
opt
, through a decrease in 〈
δ〉. However, the PL process cannot be connected with the transition between both the bands, related to formation of nanocrystals. Based on these results, it was proposed that the use of both low
T
d and high [H
2] conditions would allow to grow nc-Si:H films with small grains.