Chemical vapor deposition of PureB layers for solar cell application

A damage-free Si doping method using chemical vapor deposition of pure boron (PureB) layers is investigated for p⁺ doping of solar cell emitters. After PureB deposition the layer is thermally diffused into the Si and evaluated by determining the dopant profile, sheet resistance and effective carrier lifetime. It was found that dopant profiles and sheet resistance could be controlled by optimizing the thickness of the initial PureB layer and the subsequent annealing conditions. Compared to a boron ion implanted sample of the same sheet resistance, samples fabricated with the PureB method showed higher effective lifetime of about 300 μs as compared to 75 μs. In addition to providing defect-free junctions, PureB deposits selectively on silicon and not on silicon oxide, and may therefore be attractive for novel cell architectures.