Very High Charge Densities in Silicon Nitride Films on Silicon for Inversion Layer Solar Cells

Abstract

Different ways of achieving high positive charge densities in Si nitride films on Si for the creation of low resistivity inversion layers for solar cells are demonstrated: (i) optimization of the deposition parameters, (ii) utilizing the Si nitride charge storage effect and (iii) sodium incorporation into the nitride films. Both APCVD and PECVD Si nitride films were investigated. It was shown for the first time, that sodium can be obtained in a positively charged state in Si nitride, and, in contrast to CVD SiO2, the C-V curves were not distorted and only very small hysteresis was found after the sodium treatment. Very high charge densities up to 1.4x1013 cm-2 with stability at elevated temperatures could be achieved.