Spectra-Dependent Stability of the Passivation Quality of Al2O3/c-Si Interfaces

We examine the stability of the c-Si surface passivation quality by spatial atomic-layer-deposited aluminum oxide (Al
₂
O
₃
), plasma-enhanced chemical vapor deposited silicon nitride (SiNx), and Al
₂
O
₃
/SiNx stacks under illumination with two different spectra. The Al
₂
O
₃
-passivated c-Si surfaces annealed at 350 °C show a weak degradation due to UV illumination, with surface recombination velocities (SRVs) of 122 cm/s after receiving a ultraviolet (UV) dose of 275 kWh/m
²
. Silicon samples passivated with Al
₂
O
₃
layers that received a fast-firing step show an improvement due to UV illumination with a reduction of the SRVs initially from 14 to 5 cm/s for single Al
₂
O
₃
layers. For the fired Al
₂
O
₃
layers the negative fixed charge density increases from -6×10
¹²
cm
^-2
up to -1.2×10
¹³
cm
^-2
during UV illumination. We demonstrate that for the SiNx and the fired Al2O3 single layers, photons with energy greater than 3.4 eV are necessary to reduce the passivation quality. In contrast, low-temperature-annealed Al
₂
O
₃
single layers and nonfired Al2O3/SiNx stacks showed a degradation already under illumination with a halogen lamp. Importantly, we observe a perfectly stable passivation on boron-diffused p
⁺
emitter for fired Al
₂
O
₃
/SiNx stacks featuring a stable saturation current density of 18 fA/cm
²
for a p
⁺
sheet resistance of 90 Ω/sq.