Ultrathin SiO2/Al2O3 passivation for silicon heterojunctions using rapid thermal annealing

In this manuscript we study the surface passivation properties of ultrathin Al
₂
O
₃
in silicon heterojunctions. The Al
₂
O
₃
layer needs to be thin enough(<;1.2nm) to enable carrier collection through the passivation layer. Previous work on Al
₂
O
₃
shows that thicknesses below 10nm do not provide adequate surface passivation. In this work, we combine 0.8 nm of Al
₂
O
₃
with 1nm of SiO
₂
to improve the passivation properties of the thin Al
₂
O
₃
. The SiO
₂
helps to improve the chemical passivation by increasing the storage capacity of hydrogen with Al
₂
O
₃
, and the overall negative fixed charge of the SiO
₂
/Al
₂
O
₃
stack. Additionally, we have optimized the rapid thermal annealing in forming gas environment to activate the Al
₂
O
₃
in the SiO
₂
/Al
₂
O
₃
stack. To further increase the hydrogen in the films we deposited n-a-Si:H film before the annealing step. Effective minority-carrier lifetimes of 5 ms and implied open-circuit voltages of 723 mV were accomplished.