Thermal oxide, Al2O3 and amorphous-Si passivation layers on silicon

The effective passivation needs (1) higher bandgap than Si with type 1 alignment, (2) low interface density at the interface between passivation layer and Si, and (3) ionized charges for field effect passivation. The thermal oxide (SiO₂) with low interface defect density seems most effective but requires high growth temperature (900°C). Al₂O₃ with trapped negative fixed charges can serve as the field effect passivation. Moreover, doped amorphous Si can also have the field effect passivation with the controlled ionized charge density. The effective life time is measured by quasi-steady-state photoconductance (QSSPC). Photoluminescence (PL) measurement is consistent with QSSPC, and can probe a local area with mapping ability on large samples. The dependence of PL intensity on surface recombination velocity is theoretically studied. The passivation of a-Si becomes less effective after crystallization at high temperature annealing, indicating the larger bandgap is necessary.