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Materials Science and Engineering B73 2000 212 217 www elsevier com locate mseb Large grained polycrystalline Si films obtained by selective nucleation and solid phase epitaxy R A Puglisi 1 H Tanabe C M Chen Harry A Atwater Thomas J Watson Laboratory of Applied Physics California Institute of Technology Pasadena CA 91125 USA Abstract We investigated the formation of large grain polycrystalline silicon films on glass substrates for application in low cost thin film crystalline silicon solar cells Since the use of glass substrates constrains process temperatures our chosen approach to form large grain polycrystalline silicon templates is selective nucleation and solid phase epitaxy SNSPE In this process selective crystallization of an initially amorphous silicon film at lithographically predetermined sites enables grain sizes larger than those observed via random crystallization Selective heterogeneous nucleation centers were created for both P doped B doped and undoped 100 nm thick amorphous silicon films by masked implantation of In or Ni islands followed by annealing at temperatures below 600 C Seeded crystallization begins at the metal islands and continues via lateral solid phase epitaxy SPE thus obtaining crystallized regions of several tens of square microns The maximum achievable grain size depends on the product of the SPE rate and the incubation time for the spontaneous nucleation We have studied the dependence of the SPE rate and the incubation time on the type of metal In and Ni inducing the nucleation and on the electronic dopant e g P and B concentration in the 1019 1021 cm 3 range 2000 Elsevier Science S A All rights reserved Keywords Solar cells Si Selective nucleation Ni In 1 Introduction Polycrystalline silicon poly Si thin films are currently attracting a great deal of attention for use in solar cells Poly Si has superior carrier mobilities and stability under illumination relative to amorphous silicon a Si Since grain boundaries act as minority



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