Graded silicon nitride films: Optics and passivation

The authors describe a method for graded thin-film deposition requiring a single step that exploits the noninstantaneous replacement of reactant gases. They deposit the graded silicon-nitride films by plasma enhanced chemical vapor deposition. Channeling Rutherford backscattering measurements of the graded films find the N:Si ratio increases sixfold from the c-Si surface to air interfaces. The refractive index at the crystalline silicon/film interface was 2.96 reducing monotonically to 1.95 at the surface. The graded films achieve improved optics and surface passivation for silicon solar cells with measured surface recombination velocity of 3.9 cm/s.