Characterization of tunnel oxide passivated contact with n-type poly-Si on p-type c-Si wafer substrate

Abstract The junction properties of tunnel silicon oxide (SiO x ) passivated contact (TOPCon) with n-type poly-Si on p-type c-Si wafer are characterized using current-voltage ( J-V ) and capacitance-voltage ( C-V ) measurements. The dark J-V curves show a standard diode characteristic with a turn-on voltage of ∼0.63 V, indicating a p-n junction is formed. While the C-V curve displays an irregular shape with features of 1) a slow C increase with the decrease of the magnitude of reverse bias voltage, being used to estimate the built-in potential ( V bi ), 2) a significant increase at a given positive bias voltage, corresponding to the geometric capacitance crossing the ultrathin SiO x , and 3) a sharp decrease to negative values, resulting from the charge tunneling through the SiO x layer. The C of depleting layer deviates from the normal linear curve in the 1/C 2 -V plot, which is caused by the diffusion of P dopants from the n-type poly-Si into the p-type c-Si wafer as confirmed by the electrochemical capacitance-voltage measurements. However, the 1/C 2+γ -V plots with γ  > 0 leads to linear curves with a proper γ and the V bi can still be estimated. We find that the V bi is the range of 0.75–0.85 V, increases with the increase of the doping ratio during the poly-Si fabrication process, and correlates with the passivation quality as measured by the reverse saturated current and implied open circuit voltage extracted from transient photoconductivity decay.