Passivation Enhancement of Poly-Si Carrier-Selective Contacts by Applying ALD Al2O3 Capping Layers

Hydrogenation of polycrystalline silicon (poly-Si) passivating contacts is crucial for maximizing their passivation performance. This work presents the application of Al
₂
O
₃
prepared by atomic layer deposition as a hydrogenating capping layer. Several important questions related to this application of Al
₂
O
₃
are addressed by comparing results from Al
₂
O
₃
single layers, SiN
_x
single layers, and Al
₂
O
₃
/SiN
_x
double layers to different poly-Si types. We investigate the effect of the Al
₂
O
₃
thickness, the poly-Si thickness, the poly-Si doping type, and the postdeposition annealing treatment on the passivation quality of poly-Si passivating contacts. Especially, the Al
₂
O
₃
/SiN
_x
stack greatly enhances the passivation quality of both
n
⁺
and
p
⁺
doped as well as intrinsic poly-Si layers. The Al
₂
O
₃
layer thickness is crucial for the single-layer approach, whereas the Al
₂
O
₃
/SiN
_x
stack is less sensitive to the thickness of the Al
₂
O
₃
layer. A thicker Al
₂
O
₃
layer is needed for effectively hydrogenating
p⁺
compared to
n⁺
poly-Si passivating contact. The capping layers can hydrogenate poly-Si layers with thicknesses up to at least 600 nm. The hydrogenation-enhanced passivation for
n
⁺
poly-Si is found to be more thermally stable in comparison to
p
⁺
poly-Si. These results provide guidelines on the use of Al
₂
O
₃
capping layers for poly-Si contacts to significantly improve their passivation performance.