Deposition of phosphorus doped a-Si:H and μc-Si:H using a novel linear RF source

A roll-to-roll PECVD system for thin film silicon solar cells on steel foil has been developed by ECN in collaboration with Roth and Rau AG. It combines MW-PECVD for fast deposition of intrinsic Si and novel linear RF sources, which apply very mild deposition conditions, for the growth of doped Si layers. The RF and MW sources can be easily scaled up to deposition widths of up to 150 cm. Here, we report on n-type doping, achieved by RF-PECVD from a H-2/SiH4/PH3 mixture in the reaction chamber. The best n-type a-Si:H layers showed E-act = 0.27 eV and sigma(d) = 2.7 x 10(-3) S/cm. Also thin layers down to 20 nm were of device quality and were deposited at a rate of 0.4 angstrom/s. Furthermore, n-type mu c-Si:H layers with thicknesses of 150 nm, with E-act = 0.034 eV and sigma(d) = 2 S/cm were grown. Good quality n-type mu c-Si:H layers can be made for layer thicknesses down to 50 nm at a rate of 0.15 angstrom/s. To conclude, the novel RF source is well-suited for the growth of n-doped a-Si:H and mu c-Si:H layers for roll-to-roll solar cell production. (c) 2008 Elsevier B.V. All rights reserved.