Detailed study on the passivation mechanism of a-SixC1-x for the solar cell rear side

In this work we focus on the surface passivation of p-FZ, 1 ohm cm silicon wafers by intrinsic, silicon-rich, amorphous silicon carbide (a-SixC1-x:H) with excellent passivation quality (Seff < 5 cms-1 for p- and n-type 1 ohm cm silicon at n=5·1014 cm-3). For the purpose of extracting the effective surface recombination velocity (Seff) independent of the bulk properties, we use a set of identically passivated wafers of different substrate thickness (W). The injection-dependent carrier lifetime eff(n) is determined in a wide injection level range (1010-1017 cm-3) using a combination of the quasi-steady-state photoconductance (QSS-PC) and photoluminescence (QSS-PL) technique. Seff is extracted by evaluation of the slope of the 1/eff vs. 1/W plot for each injection level without any additional assumptions on the bulk lifetime. These pure Seff data obtained in such a way is then used within the simple Shockley-Read-Hall (SRH) model to extract surface parameters such as the interface charge density Qf. Surface photovoltage measurements (SPV) performed on the a-SiC/c-Si system confirm an amphoteric behaviour of the interface charge. Our study shows that the low-injection lifetime data determined by QSS-PL plays a crucial role for the accurate modelling of surface parameters.