Low-temperature ozone-ambient grown native oxide passivation of crystalline silicon

With continual thinning of crystalline silicon solar cells the carrier lifetime of the device becomes progressively more dependent on the quality of the surface passivation of the device. Thermal oxide growth can degrade crystalline silicon bulk properties through defect migration and can induce thermal stresses particularly in the context of ultra-thin silicon. This has motivated research into a range of passivation techniques that can be implemented at low temperatures. Here we report on the use of low temperature ozone ambient grown native oxide and PECVD grown silicon nitride bilayer structure to passivate crystalline silicon. The effective minority carrier lifetime is examined as a function of the thicknesses of the bilayers. Inferred interfacial defect and fixed charge densities are investigated vis-à-vis the native oxide and nitride layer thicknesses. Hydrogen content at the interface is determined by elastic recoil detection and Rutherford backscattering. Our results indicate that thicker silicon nitride enhances lifetime through reduced interfacial defect density albeit the trapped charge density decreases marginally with thickness. Preliminary ion spectroscopy results show a link to an increase in the hydrogen content beyond the oxide interface. Also, increasing oxide thickness grown at room temperature enhances the surface passivation.