Silicon Surface Passivation by Gallium Oxide Capped with Silicon Nitride

Advances in the passivation of p-type and p^{+} surfaces have been one of the main developments in crystalline silicon solar cell technology in recent years, enabling significant progress in p-type solar cells with partial rear contacts, and n-type solar cells with front-side boron diffusions. In this contribution, we demonstrate improvements in the passivation of p-type and boron diffused p⁺ surfaces with plasma-enhanced atomic layer deposition (PEALD) gallium oxide (Ga₂O₃) with the addition of plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN_x). On 1.6 Ωcm p-type wafers, we measure an improvement in the upper limit surface recombination velocity (S_eff,UL) from 2.5 to 1.4 cm/s on optimized Ga₂O₃ passivated samples before and after SiN_x capping. We also show an improvement in the passivation of boron diffused p⁺ surfaces over previously reported data, measuring a recombination parameter (J₀) of 26 fA/cm² on a Ga₂O₃ passivated 85 Ω/sq boron diffusion, approaching the Auger limit of ∼21 fA/cm² for this diffusion. In addition, we show that initial studies on the thermal stability of the Ga₂O₃/SiN_x stack indicate that it is compatible with conventional screen-printed metallization firing procedures.