Investigation of Degradation of Electrical Properties after Thermal Oxidation of p-Type Cz-Silicon Wafers

In this study we conducted thermal oxidation of Czochralski p-type <100> silicon wafers. The oxidation was carried out at temperatures in the range of 850-1000 degrees C, in a gas mixture of N-2: O-2, in order to deposit a thin layer (10 nm) of thermal silicon dioxide (SiO2), generally used in the surface passivation of solar cells. The measurements of effective minority carriers lifetime tau(eff) using the quasi-steady-state photoconductance have shown degradation of different samples after oxidation process. The calculation of surface recombination velocity after the oxidation process at different temperatures, gave the same value of 40 cms(-1), showing a low surface recombination velocity and, therefore, a good surface passivation. Finally, a study based on sample illumination technique, allowed us to conclude that our samples are dominated by bulk Shockley-Read-Hall recombination, caused by Fe-related centers, thereby causing the degradation of the lifetime of minority carriers.