Analysis of a-SiNx:H passivated Si surfaces based on injection level dependent lifetime and capacitance/conductance voltage measurements

Haug, H. , Helland, S. , Nordseth, Ø. , Monakhov, E.V. , Marstein, E.S.

European Photovoltaic Solar Energy Conference and Exhibition, 26, Hamburg, 2011-09-05--09-11. EU PVSEC Proceedings, 26, 1524-1529

Publ. year: 2011
Publ. type: paper
Abstract: In this paper, injection level dependent measurements of the effective surface recombination velocity (SRV) at silicon surfaces passivated with plasma-enhanced chemical vapor deposited silicon nitride films have been performed using the quasi-steady state photoconductance method. Values for the interface state density and fixed insulator charge have been extracted both by fitting the injection level dependent SRV data to an extended Shockley-Read Hall model and from direct measurements of capacitance- and conductance vs. voltage characteristics on Al/a-SiNx:H/Si structures. The relation between these microstructural parameters and the stoichiometry of the a-SiNx:H layers was determined by analyzing a series of samples produced by changing the gas flow ratio during deposition. The density of interface states was found to decrease with increasing Si-content in the layers, an effect that may be attributed to increased hydrogen content in the samples, causing an enhanced chemical passivation of dangling bonds. The fixed charge density also decreases for the more Si-rich samples, but the values are still sufficiently high to keep inversion conditions at the surface, resulting in a total lowering of the SRV with increasing Si-content. A lowering of both the interface trap density and the SRV was observed after firing for all samples.