Evaluating the impact of thermal annealing on c-Si/Al₂O₃ interface: correlating electronic properties to infrared absorption

Al₂O₃ is the standard for the passivation of p-type PERC (Passivated Emitter Rear Contact) solar cells. It is well established that the thin interfacial silicon oxide layer in between Al₂O₃ and c-Si plays a key role in its surface passivation mechanism. In this work, we investigate the interface properties of c-Si/Al₂O₃ by non-destructive methods. We show that Brewster angle Fourier transform infrared spectroscopy has a remarkable sensitivity to the interfacial silicon oxide layer by exploiting the large cross-section of the longitudinal-optic mode. These measurements show that the interfacial SiO_x layer increases in atomic density for higher annealing temperatures which coincide with an increase in negative fixed charge density (Q_f) determined from contactless capacitance-voltage measurements. X-ray photoelectron spectroscopy results show a decrease of [OH] at higher annealing temperatures which could be correlated to denser SiO_x increasing Q_f. This work provides insight into the impact of thermal annealing on the Al₂O₃/c-Si interface.