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

Abstract

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. Index Terms-Atomic layer deposition (ALD) Al 2 O 3 , hydrogenation, passivation quality, polycrystalline silicon (poly-Si) passivating contacts, thermal stability. I. INTRODUCTIONC RYSTALLINE silicon (c-Si) solar cells with polycrystalline silicon (poly-Si) as passivating contacts enable Manuscript

Hydrogen Stability and Bonding in SiNx and Al2O3 Dielectric Stacks on Poly-Si/SiOx Passivating Contacts

“…Therefore, the higher net concentration of Si–H bonds in the SiN x film must be due to the initial dissociation of Si–H bonds followed by reformation of these bonds as hydrogen is unable to diffuse as readily through the Al 2 O 3 film. This agrees with the observations in the literature ,− that Al 2 O 3 acts as a diffusion barrier to hydrogen. Interestingly, our infrared data conflicts with some assumptions in the literature that the weaker Si–H bonds (∼3.3 eV) should dissociate preferentially over the stronger N–H bond (∼4.0 eV).…”

“…Similar to SiN x , hydrogen effusion measurements for Al 2 O 3 also suggest that the deposition temperature influences the microstructure, which in turn determines the hydrogen effusion profiles. , These studies however could not conclusively identify the hydrogen-containing species that are released within the Al 2 O 3 film during firing. At the same time, Al 2 O 3 has been demonstrated to act as a barrier for the diffusion of hydrogen, ,− which can partially block in-diffusion and out-diffusion of hydrogen in Al 2 O 3 /SiN x stacks. However, how the barrier properties of Al 2 O 3 influence the passivation of poly-Si/SiO x passivating contacts is not well understood.…”

Poly‐SiOx Passivating Contacts with Plasma‐Assisted N2O Oxidation of Silicon (PANO‐SiOx)

“…At the SiO x interface an accumulation of hydrogen atoms was found. [ 66 ] The hydrogen content of the PANO‐SiO x sample at the interface is 1.3 × 10 20 atoms cm −3 , which is slightly higher than the NAOS‐SiO x ‐based sample. The PANO‐SiO x , with its higher Si 4+ content with respect to NAOS‐SiO x , can effectively prevent the in‐diffusion of hydrogen toward the c‐Si bulk, retain more hydrogen on the surface, and thus better chemically passivate the interface dangling bonds.…”

Effect of films thickness and hydrogen annealing on passivation performance of plasma ALD based Hafnium oxide films

“…SiN x [9], a-Si:H [10], ZnO [11], Al 2 O 3 [12,13], HfO 2 [14][15][16]. Although the pros and cons of these dielectrics have been discussed in numerous publications in the past few decades [17,18], the discovery of alternative effective passivation materials is a strong driving force for research.…”