Impact of Implanted Phosphorus on the Diffusivity of Boron and its Applicability to Silicon Solar Cells: Article No. 045702

Robert Reedy Jr., Julian Schrof, Ralph Muller, Jan Benick, Martin Hermle

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Boron diffusivity reduction in extrinsically doped silicon was investigated in the context of a process combination consisting of BBr3 furnace diffusion and preceding Phosphorus ion implantation. The implantation of Phosphorus leads to a substantial blocking of Boron during the subsequent Boron diffusion. First, the influences of ion implantation induced point defects as well as the initial P doping on B diffusivity were studied independently. Here, it was found that not the defects created during ion implantation but the P doping itself results in the observed B diffusion retardation. The influence of the initial P concentration was investigated in more detail by varying the P implantation dose. A secondary ion mass spectrometry (SIMS) analysis of the BSG layer after the B diffusion revealed that the B diffusion retardation is not due to potential P content in the BSG layer but rather caused by the n-type doping of the crystalline silicon itself. Based on the observations the B diffusion retardation was classified into three groups: (i) no reduction of B diffusivity, (ii) reduced B diffusivity, and (iii) blocking of the B diffusion. The retardation of B diffusion can well be explained by the phosphorus doping level resulting in a Fermi level shift and pairing of B and P ions, both reducing the B diffusivity. Besides these main influences, there are probably additional transient phenomena responsible for the blocking of boron. Those might be an interstitial transport mechanism caused by P diffusion that reduces interstitial concentration at the surface or the silicon/BSG interface shift due to oxidation during the BBr3 diffusion process. Lifetime measurements revealed that the residual (non-blocked) B leads to an increased dark saturation current density in the P doped region. Nevertheless, electrical quality is on a high level and was further increased by reducing the B dose as well as by removing the first few nanometers of the silicon surface after the BBr3 diffusion
Original languageAmerican English
Number of pages10
JournalJournal of Applied Physics
Issue number4
StatePublished - 2015

NREL Publication Number

  • NREL/JA-5K00-64954


  • furnaces
  • interstitial defects
  • ion implantation
  • silicon
  • silicon doping


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