Improving ALD-Al2O3 Surface Passivation of Si Utilizing Pre-Existing SiOx
IEEE Journal of Photovoltaics(2022)
摘要
Al
2
O
3
has rapidly become the surface passivation material of choice for
p
+ layers of solar cells because of its high negative fixed charge, good long-term and thermal stability, and no parasitic absorption. In this article, the surface saturation current density, fixed charge, and interface state density are compared for Al
2
O
3
deposited on Si substrates where the pre-existing out-of-the-box SiO
x
layer was not removed, with substrates where the SiO
x
was removed by hydrofluoric acid. The depositions are performed by atomic layer deposition at temperatures in the 150–300 °C range, using trimethylaluminium, H
2
O, and O
3
as precursors. The samples where the native oxide was not removed achieve a higher level of surface passivation for every tested deposition temperature, with the sample deposited at 200 °C exhibiting a surface saturation current density of only 0.9 fA/cm
2
after annealing, a fixed charge of −4.2 × 10
12
cm
−2
, and a density of interface states of 9.8 × 10
9
cm
−2
eV
−1
. Capacitance and conductance voltage characteristics reveal a strong correlation between the surface saturation current density and the density of interface states and fixed charges. It is also determined that the long-term stability of the surface passivation depends on the deposition temperature, with higher deposition temperatures resulting in improved long-term stability. The results indicate that H-terminated Si prior to Al
2
O
3
deposition may have a detrimental effect on the surface passivation.
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关键词
$\mathbf{Al}_{\mathbf 2}{\mathbf O}_{\mathbf 3}$ growth rate,effect of HF-dip,long-term stability $\mathbf{Al}_{\mathbf 2}{\mathbf O}_{\mathbf 3}$ ,optimal deposition temperature $\mathbf{Al}_{\mathbf 2}{\mathbf O}_{\mathbf 3}$ ,out-of-the-box silicon oxide,surface passivation,TMA + ${\mathbf O}_{\mathbf 3}+ {\mathbf H}_{\mathbf 2}{\mathbf O}$ ALD
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