Epitaxial growth of radial Si p-i-n junctions for photovoltaic applications

Achieving high quality radial junctions in nanowire arrays with controlled doping profiles is critical for their potential photovoltaic applications. We present a low temperature epitaxial growth process for silicon radial p-n and p-i-n junction arrays on top-down fabricated nanowires using silane-based chemical vapor deposition. Epitaxial growth on [111] oriented nanowires of ∼300 nm diameter and up to 10 μm in length exhibits well-defined, single crystalline {110} faceted surfaces at temperatures as low as 710°C. The growth rate G at 810°C for intrinsic Si is greater than that for heavily B- and P-doped Si (G_i > G_p > G_n). Faceted growth morphology at the tip of the nanowires results in well-defined match-head structures for undoped and B-doped growth. Preliminary photovoltaic device arrays of ∼4 × 10⁴ nanowires based on our radial epitaxial p-i-n junction growth approach achieve solar energy conversion efficiencies of 10 under AM 1.5 G illumination.