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 (Ga
₂
O
₃
) 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 (
$S_{{\rm eff, \text{UL}}}$
) from 2.5 to 1.4 cm/s on optimized Ga
₂
O
₃
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 (
$J_{0}$
) of 26 fA/cm
²
on a Ga
₂
O
₃
passivated 85 Ω/sq boron diffusion, approaching the Auger limit of ∼21 fA/cm
²
for this diffusion. In addition, we show that initial studies on the thermal stability of the Ga
₂
O
₃
/SiN
_x
stack indicate that it is compatible with conventional screen-printed metallization firing procedures.