Films minces à base de Si nanostructuré pour des cellules ...

tel-00916300, version 1 - 10 Dec 2013
Figure 3.3: Proposed mechanism of temperature dependent reactive sputtering.
As a consequence of an increase in hydrogen velocity with increasing T d as compared
to other species, Si deposition is favoured. This is attributed to the increased
reaction of hydrogen in reducing the sputtered oxygen species which move towards
the substrate at a lower velocity. This explains the continuous rise in the n 1.95eV
as the Si content in SRSO layer increases with T d . The role of hydrogen is not
restricted to deposition, but also towards an etching mechanism since the weak and
strained Si-Si bonds are broken leading to removal of Si atoms from the surface
[Tsai 89, Akasaka 95]. Hence, with increased velocity, it is also probable that hydrogen
reaches the lm growing surface faster than the other Si or O atoms thereby
forming Si-H bonds faster than Si-Si bonds. This leads to a continuous etching
process resulting in a decreased r d . Thus, the competing etching mechanism seems
to be predominant at T d ranging between 200°C to 400°C.
At elevated temperatures, between T d = 425°C to 600°C, in addition to the process
described above, the temperature allows the formation of Si-Si bonds since
hydrogen from Si-H dissociates into Si and H 2 [Veprek 79]. This explains the decrease
of r d and concomitant increase of refractive index.
Increasing time and temperature of deposition facilitates the reorganization of
the Si-Si bond into a network which could also lead to the agglomeration of few
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