Properties of amorphous Si-rich silicon nitride prepared by rf-magnetron sputtering

This article investigates the physics underlying field effect passivation of p-type Si surfaces coated with SiNx(:H) of various Si contents. We find a correlation between the effective lifetime of minority carriers in p-type Si passivated with SiNx, on the one hand, and the dark dc-conductivity data of corresponding a-SiNx-films with different composition, on the other hand. By increasing the amount of Si in a-SiNx(:H) structures the bandgap decreases from about 5 to 2 eV. As a result, the dark dc-conductivity rises by several orders of magnitude. The conductivity prefactors and the activation energies as calculated from the conductivity versus temperature data obey the Meyer–Neldel relation with an axio-intercept of about 10−7 (Ωcm)−1 and a slope of about 35 meV. Thus, Si-rich a-SiNx(:H) films behave like a defect doped n-type semiconductor. The activation energy of the conductance in films with the same composition changes with the hydrogen content. A minimum in the activation energy correlates with a minimum of the surface recombination velocity at the a-SiNx/p-Si interface. We ascribe both effects to a variation of the Fermi level in the films.