SPLTRAK Abstract Submission
Investigating the impurity gettering rate in polycrystalline-silicon based passivating contacts
Zhongshu Yang1, Jan Krügener2, Frank Feldmann3, Jana-Isabelle Polzin3, Bernd Steinhauser3, Tien T. Le1, Daniel MacDonald1, AnYao Liu1
1School of Engineering, The Australian National University, Canberra, Australia
/2Institute of Electronic Materials and Device, Leibniz University Hannover, Hannover, Germany
/3Fraunhofer Institute for Solar EnergySystems ISE, Freiburg, Germany

Polycrystalline-silicon/oxide (poly-Si/SiOx) passivating contacts for high efficiency solar cells exhibit excellent surface passivation, carrier selectivity, and impurity gettering effects. However, the ultrathin SiOx interlayer can act as a diffusion barrier for metal impurities and this potentially slows down the overall gettering rate of the poly-Si/SiOx structures. Herein, the factors that determine the blocking effects of the SiOx interlayers are identified and investigated by examining two general types of the SiOinterlayers: 1.3-nm ultrathin tunneling SiOx with negligible pinholes and 2.5-nm SiOx with thermally created pinholes. Iron is used as a tracer impurity in silicon to quantify the gettering rate. By fitting the experimental gettering kinetics by a diffusion-limited segregation gettering model, the blocking effects of the SiOx interlayers are quantified by a transport parameter. Both the oxide stoichiometry and pinhole density affect the effective transport of iron through SiOx interlayers. The oxide stoichiometry depends strongly on the oxidation method, while the pinhole density is affected by the activation temperature, doping concentration, doping technique, and possibly the dopant type as well. To enable a fast gettering process during typical high-temperature formation of the poly-Si/SiOstructures, a SiOx interlayer that is less stoichiometric or with a higher pinhole density is preferred.