Investigation of Thermal Stability and Internal Fixed-Charge State for Field Effect Passivation Layer of Strontium Silicate on Silicon Substrate

28th European Photovoltaic Solar Energy Conference and Exhibition; 1545-1547
Strontium silicate (SrSiOx) is one of candidates to be a field effect passivation layer with positive fixed-charges (FCs). In this study, we provide systematic investigations of thermal stability and internal FC state for SrSiOx layer grown on crystalline silicon (c-Si) substrate. The SrSiOx layers were fabricated by growing SrO layers on Si substrates using pulsed laser deposition, and then post-annealing treatment (PAT) in oxygen atmosphere. To investigate the thermal stability of the samples, the PAT was carried out at various temperatures from 500800. From x-ray photoemission spectroscopy measurements, we identified that the SrSiOx/Si structure was maintained after the PAT below 700, but SiOx layer began to grow at the interface above 800. The internal FC state was evaluated by capacitance-voltage (C-V) measurements for samples having various thickness of SrSiOx layer. Negative flat band voltage shift (NFBVS) was observed in the SrSiOx/Si samples annealed at 600 . In the samples with a longer PAT above 2 hours, the effective FC density estimated from the magnitude of the NFBVS was almost constant (1×1012 cm-2) against the thickness variation. From these results, we consider that the origins of the NFBVS would be likely due to intrinsic positive FC existing in the vicinity of the SrSiOx/Si interface. For the interface FC, it is independence from the SrSiOx thickness, and we can freely design FEP layer thickness without constraint. This would provide the degree of freedom in the cell design including anti-refection layers.