Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride

A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiN_x) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiN_x stack, recombination current density J₀ values of 9, 11, 47, and 87 fA/cm² are obtained on 10 Ω·cm n-type, 0.8 Ω·cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J₀ on n-type 10 Ω·cm wafers is further reduced to 2.5 ± 0.5 fA/cm² when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiN_x stack is thermally stable at 400 °C in N₂ for 60 min on all four c-Si surfaces. Capacitance-voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiN_x stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.