Passivation mechanisms of amorphous SixC1-x layers on highly doped and textured Si surfaces
Lifetime measurements by means of the Quasi Steady State Photo Conductance technique (QSS-PC) were carried out in order to gather further insight into the passivation performance of amorphous SixC1-x:H on textured and highly doped silicon surfaces. The set of lifetime samples used in this experiment consisted of shiny etched p-FZ, 1 ohm cm wafers with <100> crystallographic orientation, that were either textured (random pyramid structure) and/or phosphorous diffused (120 ohm/sq) on both sides. A comparison of flat and textured emitter samples shows a constant shift to lower effective lifetimes for textured surfaces independently of the thickness of the a-SixC1-x layer. Different growth times of native oxide on silicon surfaces after treatment in HF solution (5%) prior to deposition of the a-SixC1-x layer reveal to have major impact on the effective lifetime of the samples. This uncertainty was sought to be cancelled out by applying an in-situ plasma pre-cleaning process to wafers that were taken directly out of box (shiny etched) and thereby abandoning any wet-chemical pre-treatment. In fact, very high lifetimes exceeding 1 ms on 1 ohm cm for an injection level of 5x10(exp 14) cm-3 were achieved on flat samples whereas plasma pre-treatment showed hardly any effect on textured surfaces. Finally, first tests using a SixC1-x double layer system consisting of an excellent passivating Si-rich and a robust stoichiometric SiC layer were performed. Although the second layer deposition involves high microwave and high-frequency power densities, hardly any degradation in the performance of the passivating layer could be observed.