Excellent Passivation of p-Type Si Surface by Sol-Gel Al₂O₃ Films

Al₂O₃ films with a thickness of about 100nm synthesized by spin coating and thermally treated are applied for field-induced surface passivation of p-type crystalline silicon. The level of surface passivation is determined by techniques based on photoconductance. An effective surface recombination velocity below 100cm/s is obtained on 10Ω·cm p-type c-Si wafers (Cz Si). A high density of negative fixed charges in the order of 10¹²cm^-2 is detected in the Al₂O₃ films and its impact on the level of surface passivation is demonstrated experimentally. Furthermore, a comparison between the surface passivation achieved for thermal SiO₂ and plasma enhanced chemical vapor deposition SiN_x:H films on the same c-Si is presented. The high negative fixed charge density explains the excellent passivation of p-type c-Si by Al₂O₃.