Effects of fluorine incorporation on the properties of amorphous carbon/p-type crystalline silicon heterojunction diodes

Heterojunction diodes fabricated by plasma enhanced chemical vapor deposition of hydrogenated amorphous carbon (a-C:H) and fluorine-doped amorphous carbons (a-C:H:F) on p-type silicon are analyzed in terms of their electronic and photovoltaic properties. Their structural and optical properties were identified by Raman spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and UV-VIS transmittance. The nature of the heterojunction is confirmed by the rectifying current-voltage characteristic of carbonaceous deposits/p-Si junction. The diodes show a behavior dependent on the amount of the fluorine content. The photovoltaic behavior of the junction is investigated as a function of both fluorine incorporation and thermal treatment of the a-C:H:F films after the deposition. Better photovoltaic effects were observed from annealed a-C:H:F heterojunction structures. The optical and structural characterization performed on films after the thermal treatment indicates that this behavior is most likely due to an extended graphitization. (C) 2003 Elsevier Science B.V. All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-2010